Chemistry Demos
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A light bulb will glow when a substance that conducts electricity is inserted in a break in the wires that leads to and from the power source.
Solutions that contain ionic compounds conduct electricity. The more a compound separates into its ionic units, the more ions there are in solution. The more ions there are, the more electricity that flows through the solution. For example, the acetic acid will light the bulb dimly and the hydrochloric acid will light the bulb more brightly due to its higher Ka value.
A light dims as Barium Hydroxide is added to Sulfuric Acid. Once the endpoint of this reaction is reached, the light goes out, and shortly after, the phenolphthalein indicator added turns pink.
Solutions that contain ionic compounds conduct electricity. When Barium Hydroxide is added to Sulfuric Acid, insoluble Barium Sulfate and water are produced.
About 30 seconds after the acid is added to the sugar, a column of black carbon grows up from the beaker. There are vapors and the smell of burned sugar.
Sulfuric acid is a strong acid and has a strong affinity for water.
The pH of some common household acids and bases are measured and compared.
pH can be used as a measurement of acidity and basicity.
Red cabbage juice will change to a variety of colors when added to solutions of various pH.
Red cabbage juice is a pH indicator.
NaOH and HCl are used to titrate tablets of Alka-Seltzer and to titrate plain water. The Alka-Seltzer acts as a buffer. More base and acid is required to bring the Alka-Seltzer solutions to a basic or acidic pH.
A buffer resists changes in pH when acid or base are added.
Six wine glasses are filled with the same 'mystery' liquids. Each glass takes on a different color of the rainbow, despite the fact that the same liquids were added to each. Each glass is treated with a specific mixture of indicators before the demo is performed.
In each case, the deprotonation on an OH group causes the color change to arise. The indicators provide the primary colors that are a base for the orange, green and violet.
Four beakers (or crystallizing dishes) are filled to the same level: two contain water while two contain acetate buffer. Indicators are added to each. Acid and base are added to the water-filled beakers and to the buffer-filled beakers. No color change can be observed in the buffer-filled beakers.
The addition of strong acid or base to the buffer system will not affect the pH by a very large degree, since acid addition results in the production of a weaker acid and water, and base addition results in the production of a weaker base and water.
A crystallizing dish with an eye drawn on the bottom surface is placed on an overhead projector. Egg white is put into the dish, and when acid is added, the egg white clouds up to simulate what an acid would do to one’s eye. Sodium bicarbonate is dropped onto the spots where acid has been added to simulate what happens when someone tries to “undo” the damage that acid causes.
The egg white is transparent and made up of protein just like the layer over our eye. When the acid is added, these proteins (albumin in the egg) are denatured. Adding sodium bicarbonate solution cannot undo the damage. The proteins cannot be rebuilt.
Equal amounts of colorless, clear liquids are added to three cylinders containing calcium carbonate solid or sodium bicarbonate solution. One cylinder immediately fills with bubbles, the second fills with bubbles within a few seconds, and the third fills with bubbles only after about 10-15 seconds.
Acetic acid is a weak acid and hydrochloric acid is a strong acid. When equal number of moles of these two acids dissociate, there are more hydronium ions produced from hydrochloric acid (cylinder 1) than there are from acetic acid (cylinder 2). The addition of the common ion acetate reduces the acidity of acetic acid by shifting the equilibrium to the left reducing the amount of acetic acid that will dissociate (cylinder 3).
CaCO3 precipitate is produced and then dissolved when a strong acid (HCl) is added. Bubbles of gas are also observed when the acid is added.
As CO3 2- ions react with the acid, according to Le Chatelier’s Principle, the solid CaCO3 dissolves.
A sodium hydroxide solution is added to a PET soda bottle that is filled with CO2. The bottle is quickly capped and shaken. The bottle collapses.
Carbon dioxide reacts with sodium hydroxide. As CO2 gas is removed from the closed bottle, the pressure inside the bottle decreases. The atmospheric pressure on the outside remains the same and will collapse the bottle.
Two clear and colorless solutions are combined and a white precipitate appears. Aqueous ammonia is added and the precipitate is dissolved.
The solubility of AgCl in aqueous ammonia is determined by the product of the 'solubility product' of AgCl and the 'formation constant' of Ag(NH3+). This product is only 0.0027. 1.0 M ammonia will only 'hold”' 0.047 M Ag+ in the presence of AgCl precipitate (when there is no excess chloride).
Several types and colors of markers are spotted onto chromatography paper and allowed to develop for 10-15 minutes in a chamber containing water as the mobile phase.
A mixture of chemicals can be separated based on their relative affinities for the chromatography paper and solvent.
A deep, yellow-green extract derived from raw spinach is eluted through a chromatography column containing silica. The result is a separation of the ?-carotene and chlorophyll pigments in the spinach. When completed, the students should be able to see distinct yellow and green bands in the column.
Molecules contained within a mixture can be separated based on their differing affinities for various solvents.
CaCl2 and Na2CO3 are weighed together before and after they are mixed to form a precipitate to show that mass is conserved.
The total mass of substances does not change during a chemical reaction. When one volume of liquid is mixed with another volume of liquid that is less dense than the first, the total volume of the two liquids will not be the sum of the two individual liquids. The molecules of one liquid can fill in the volume between the molecules of another.
Green food coloring (a mixture of food dyes Blue 1 and Yellow 5) is separated into its components using a C18 Sep Pak and various mixtures of methanol and water.
A nonpolar stationary phase is used for reverse-phase chromatography. The material contained in the Sep Pak cartridge is relatively nonpolar, and will retain other nonpolar molecules.
Total brand cereal is ground into a powder and stirred with a magnetic stir bar in water. Minutes later, the stir bar is pulled out to reveal iron filings that had been put into the cereal as a nutritional supplement. As an alternative demonstration, the ground cereal can be placed in a small vial suspended from a string. The iron in the cereal will cause the vial to be attracted to a gap magnet.
Iron metal is often added to breakfast cereals as a nutritional supplement. Since iron is paramagnetic, it will be attracted to a magnetic field.
Description: Na and Mg metals react with oxygen to produce basic oxides that turn universal indicator purple (basic). Carbon on the other hand reacts with oxygen to produce an acidic oxide that turns universal indicator orange (acidic).
Concept: Most metals react with oxygen to produce basic oxides. Most non-metals react with oxygen to produce acidic oxides.
Lithium, sodium, and potassium metals are sliced and then a small sample of each is reacted with water.
The alkali metals are soft and silvery. They are also the most reactive metals having the lowest ionization energies. They react readily with water, lithium being the least reactive and potassium the most.
Samples of Mg and Ca are displayed. Mg and HCl produce less bubbles than Ca and HCl. Mg and H2O produces less hydroxide and therefore less pink with phenolphthalien than Ca and H2O.
The alkaline earth metals are less reactive and harder compared to the alkali metals. They do not react as readily with water. Mg is less reactive than Ca.
Many samples of elements are available to be displayed in class.
An element is a substance that cannot be decomposed by any chemical reaction into simpler substances; a type of matter composed of only one kind of atom, each atom of a given kind having the same properties.
Small cards showing each element and their atomic number are arranged to form the periodic table.
When the elements are arranged by atomic number, their physical and chemical properties such as atomic radius, ionization energy and electron affinity, vary periodically.
Several samples of alkanes are displayed.
The physical properties of the alkanes are related to their molecular structure.
Tollen’s Reagent is added to two flasks. A dextrose water solution is added to one and swirled. The contents of the flask turn brown and then silver is plated onto the inside of the flask. Sucrose is added to the other flask. The contents may turn brown but no silver is plated.
Silver (I) is reduced to silver metal by aldehydes but not by ketones.
A few students are given a piece of Bazooka bubble gum that has been pre-weighed and asked to chew the gum for about 20 minutes. After 20 minutes the pieces of gum are weighed again.
The molar mass (molecular weight) of sugar (sucrose) is large, 342.30 g/mol.
A pickle is placed into a light socket and a tungsten electrode is put through the top. The lights are turned low and current is sent arcing through the pickle from a variac that had been plugged into a wall outlet. The pickle glows brightly for a few seconds and eventually starts to smoke.
The pickling process involves soaking a cucumber in a concentrated salt solution (or brine). Water flows out of the cucumber and salt flows into the cucumber, creating a salty, dehydrated cucumber (or pickle). The inside of the pickle is essentially an electrolyte solution, and conducts electricity.
A light bulb will glow when a substance that conducts electricity is inserted in a break in the wires that leads to and from the power source.
Solutions that contain ionic compounds conduct electricity. The more a compound separates into its ionic units, the more ions there are in solution. The more ions there are, the more electricity that flows through the solution. For example, the acetic acid will light the bulb dimly and the hydrochloric acid will light the bulb more brightly due to its higher Ka value.
A light dims as Barium Hydroxide is added to Sulfuric Acid. Once the endpoint of this reaction is reached, the light goes out, and shortly after, the phenolphthalein indicator added turns pink.
Solutions that contain ionic compounds conduct electricity. When Barium Hydroxide is added to Sulfuric Acid, insoluble Barium Sulfate and water are produced.
Equal amounts of colorless, clear liquids are added to three cylinders containing calcium carbonate solid or sodium bicarbonate solution. One cylinder immediately fills with bubbles, the second fills with bubbles within a few seconds, and the third fills with bubbles only after about 10-15 seconds.
Acetic acid is a weak acid and hydrochloric acid is a strong acid. When equal number of moles of these two acids dissociate, there are more hydronium ions produced from hydrochloric acid (cylinder 1) than there are from acetic acid (cylinder 2). The addition of the common ion acetate reduces the acidity of acetic acid by shifting the equilibrium to the left reducing the amount of acetic acid that will dissociate (cylinder 3).
Two ~ 1 ft long glass tubes containing a reddish colored gas and put in a dry-ice-isopropy alcohol bath. The tubes loose their gas and a green liquid condenses on the bottom. When one tube is returned to room temperature, its reddish color is restored.
NO2 gas exists as a mixture of NO2 and N2O4 at equilibrium. It is a reddish color. When the temperature is changed the equilibrium shifts. Cooling the gas, causes a shift towards the dimer, N2O4, which should be colorless when pure but can be blue-green due to impurities such as N2O3. The dimerization in NO2 is exothermic.
A green aqueous Nickel Nitrate solution turns blue upon the addition of Ammonia and than back to green when Hydrochloric acid is added. Sometimes it has been observed that a precipitate forms when the ammonia is added, which dissolves with acid.
When the concentration of any of the species in an equilibrium system is changed, the equilibrium is disturbed and the system will react so as to minimize the effect of the disturbance.
Co(H2O)62+, which is pink in color, is converted to a blue CoCl42- complex through the addition of NH4Cl. The resulting blue liquid is separated from undissolved NH4Cl, and a little H2O is added, shifting the color from blue to pink again. The reaction can be repeated multiple times.
When the concentration of any of the species in an equilibrium system is changed, the equilibrium is disturbed and the system will react so as to minimize the effect of the disturbance.
The Collisions Cube is set up to demonstrate chemical equilibrium. If the blower powers are equal, an even distribution of each color should be established in each chamber. Adjusting one blower to roughly half the power of the other will cause the ping-pong balls to begin accumulating on the side with less blower power. Once equilibrium is established, roughly 1/3rd of the balls should be on one side while the other 2/3rd will be on the other side. The net change in the system at this point should still be about zero if observed closely.
Equilibrium is a state in which the new change in a system is 0. Equilibrium doesn’t necessarily mean having equal amounts of reactant and product.
When the blowers of the Collisions Cube are turned on, the balls will mix and distribute themselves evenly among the two sides. The power of this demonstration lies in the question that should be asked after mixing has occurred: "How long do we need to leave the machine running before we will see the ping-pong balls separate into groups of like colors once more?" It can be noted that un-mixing the balls will take a bit of effort and will not occur without some type of outside force interfering and using up energy.
Entropy is a measure of incapability for a reaction to do further work.
A bottle has two nails poking inside such that the points of the nails almost touch. A couple mL of methanol are put in the bottle and the bottle is corked and gently shaken and then clamped to a ring stand. A tesla coil is applied to the head of one of the nails. Almost immediately the methanol is ignited and the cork is shot into the air. Quickly the instructor corks the bottle. The bottle is shaken and the tesla coil is applied, but nothing happens. Why not? Then the instructor blows into the bottle, shakes, and uses the tesla coil to once again shoot the cork. Why does it work again?
Oxygen is required for the combustion of methanol. Also molecules in the vapor phase are farther apart than in the liquid phase and present more surface area for reaction.
One kilogram and 100 g samples are displayed to compare their sizes. A liter beaker is displayed to show its size. One mole samples of various elements and compounds are displayed. One mole of NaCl and 1 Liter beaker are shown in relationship together to demonstrate molarity.
A mole is not a measurement of a static amount of material.
A sugar cube will not burn unless it is first rubbed with ash.
Ashes catalyze the burning of sugar. A catalyst speeds up a reaction.
Three colorless solutions are mixed together. The color of the resulting mixture will oscillate back and forth from amber to blue for about 5 minutes. The reaction ends as a blue-black mixture with the odor of iodine.
The basic concept that this reaction demonstrates is that two reactions can switch back and forth. The product of one is the reactant for the other.
Oxidation of Potassium Iodide by Hydrogen Peroxide
Two colorless solutions are mixed. After 10 seconds, the colorless mixture suddenly turns blue.
Demonstrates a typical clock reaction; shows the effect of the interaction between chemical reactions that have different rates.
1.) An amount of manganese dioxide is added to a flask containing hydrogen peroxide. In a few minutes steam pours up vertically from the flask. 2.) Hydrogen peroxide is added to a large graduated cylinder containing liquid soap and sodium iodide. Yellow foam quickly rises in the cylinder, overflowing into a tub.
1.) Manganese dioxide catalyzes the decompostion of hydrogen peroxide. 2.) The iodide anion catalyzes the decomposition of hydrogen peroxide. The oxygen produced creates soap bubbles in this exothermic process.
A hot, glowing platinum wire appears to "explode" or poof when placed inside a flask containing a small amount of methanol. After the explosion the wire stops glowing but within about 10 seconds it will start to glow again and then poof....
Platinum catalyzes the oxidation of methanol. This oxidation occurs on the surface of the platinum wire and causes the wire to glow red. Eventually it will get so hot that their will be a small methanol explosion. The oxygen in the flask is consumed in this explosion, thus stopping the oxidation reaction. When oxygen diffuses back into the flask the oxidation begins again causing the platinum to glow and then an explosion...
The contents of a series of flasks are mixed together and eventually each mixture will change from colorless to blue after a different amount of time. Segments of the Willian Tell Overture by Rossini are played as the chemicals are mixed and the mixtures change colors. The goal is to get the final flask to change color at the end of the music.
By varying the amounts of the chemicals the clock reaction will complete at various times. The rate of a reaction is affected by the concentrations of the reactants.
Lycopodium powder is shown to be combustable when sprinkled onto a flame. A lit match comes in contact with a pile of lycopodium on a watch glass with little results. The same amount of powder is dumped into a cardboard tube with a lit candle at the bottom, and the result is a column of flame.
A fine mist of dust can be highly flammable because of the high surface area of the combustible (the dust) to the oxidizer (the air). The rate of reaction is proportional to surface area.
A pink CoCl2 solution is added to a Tartaric Acid solution in the presence of H2O2. As the reaction progresses, O2 and CO2 bubbles rapidly evolve and a green cobalt-tartrate intermediate can be observed. Once the reaction is complete, the catalyst (CoCl2) returns to its original pink color.
A pink CoCl2 solution is added to a Tartaric Acid solution in the presence of H2O2. As the reaction progresses, O2 and CO2 bubbles rapidly evolve and a green cobalt-tartrate intermediate can be observed. Once the reaction is complete, the catalyst (CoCl2) returns to its original pink color.
Lycopodium powder is squeezed from a squirt bottle into a candle flame, and is shown to be readily ignitable. Another portion of lycopodium powder is poured to form a small mound on a watch glass. A match is touched to the pile of lycopodium and, to the surprise of the class, fizzles a little, but never completely combusts. The candle is then set onto the ground and lit. A long cardboard tube is set over the candle, and lycopodium powder is dropped into the tube from a notecard. A small explosion occurs and flames shoot from the top of the tube.
Lycopodium powder is made up of waxy spores from club moss. It was once used as flash powder in early photography. When the powder is squirted into a flame, much of its surface area is exposed to the oxygen in the air and is readily combustible. The surface area exposed to oxygen is greatly reduced when the powder is in a pile, and only the grains on the surface of the pile will ignite.
The blowers in the Collisions Cube are set at low power on each side. The side with the ping-pong balls is said to represent reactants, while the empty side is said to represent products. The power should be low enough so that no ping-pong balls change sides. The hole at the top is representative of the energy barrier that reactant molecules must overcome in order for the reaction to proceed. The students are asked to propose a change to the system that would allow for product creation.
Product creation is sometimes limited by the amount of activation energy provided.
A solution of t-butyl chloride in acetone is added to water in the presence of a base and universal indicator. Depending on the concentration of t-butyl chloride, the reaction to form t-butyl alcohol is indicated by a series of drastic color changes.
The color change occurs as aqueous chlorine removes a proton from the transition state, resulting in a lower pH of the system (see mechanism in “concept” section). This demonstration can also qualitatively show that the rate of reaction is dependant of the concentration of t-butyl chloride.
Tollen’s Reagent is added to two flasks. A dextrose water solution is added to one and swirled. The contents of the flask turn brown and then silver is plated onto the inside of the flask. Sucrose is added to the other flask. The contents may turn brown but no silver is plated.
Silver (I) is reduced to silver metal by aldehydes but not by ketones.
A colorless liquid is added to a yellow liquid. The mixture turns pink and foams. Alternatively, acid and powdered carbonate are mixed in a corked test tube and pressure resulting from the gas generated pushes the cork out of the test tube.
When acids and carbonates react carbon dioxide gas is generated.
Carbon dioxide gas from a cylinder is bubbled through limewater and calcium carbonate solid is formed causing the limewater to become cloudy. Catch carbon dioxide gas in a jar from a burning bunsen burner. Pour in fresh limewater and it will become cloudy indicating that there was in fact CO2 in that jar.
Methane when burned reacting with oxygen produces carbon dioxide gas (1).
A number of different types of chemical reactions are demonstrated.
Observations of what happens when two chemicals are mixed together can clue us to if and how the chemicals react.
Ice is put in a bowl of water and Universal Indicator and allowed to ?melt?. The color of the indicator changes from green (neutral) to orange (slightly acidic). Drops of NaOH are added until the color of the indicator is green or blue (basic pH). Alternatively, dry ice can be added to water that contains a few drops of NaOH and the color will change from blue (basic) back to orange (slightly acidic).
Dry ice is solid CO2 and when it is put in water, the CO2 combines with the water to form carbonic acid (H2CO3).
A copper wire coil in a Christmas tree shape is allowed to sit in a solution of silver nitrate. Within an hour silver metal needles form on the wire.
Copper metal is oxidized by the Ag1+ to Cu2+ and the Ag1+ ions are reduced by the copper metal to silver metal.
A light bulb will glow when a substance that conducts electricity is inserted in a break in the wires that leads to and from the power source.
Solutions that contain ionic compounds conduct electricity. The more a compound separates into its ionic units, the more ions there are in solution. The more ions there are, the more electricity that flows through the solution. For example, the acetic acid will light the bulb dimly and the hydrochloric acid will light the bulb more brightly due to its higher Ka value.
A light dims as Barium Hydroxide is added to Sulfuric Acid. Once the endpoint of this reaction is reached, the light goes out, and shortly after, the phenolphthalein indicator added turns pink.
Solutions that contain ionic compounds conduct electricity. When Barium Hydroxide is added to Sulfuric Acid, insoluble Barium Sulfate and water are produced.
A small chunk of phosphorus is ignited by flame and quickly plunged into a flask containing oxygen gas. The resulting reaction produces heat, smoke and a spectacular bright light that last for 5-10 seconds.
Finely dispersed phosphorus will readily ignite in the presence of oxygen at room temperature and must be stored under water or in a solvent such as carbon disulfide.
Red cabbage juice will change to a variety of colors when added to solutions of various pH.
Red cabbage juice is a pH indicator.
A sodium hydroxide solution is added to a PET soda bottle that is filled with CO2. The bottle is quickly capped and shaken. The bottle collapses.
Carbon dioxide reacts with sodium hydroxide. As CO2 gas is removed from the closed bottle, the pressure inside the bottle decreases. The atmospheric pressure on the outside remains the same and will collapse the bottle.
Oxidation of Potassium Iodide by Hydrogen Peroxide
Two colorless solutions are mixed. After 10 seconds, the colorless mixture suddenly turns blue.
Demonstrates a typical clock reaction; shows the effect of the interaction between chemical reactions that have different rates.
A Gummi Bear is dropped into a test tube of heated potassium chlorate. The Gummi Bear is combusted.
Exothermic reactions produce a lot of heat. Potassium Chlorate is a strong oxidizing agent; a fire may start when it is mixed with combustible materials.
A small amount of water is squirted into an inverted round-bottomed flask full of ammonia gas. This flask is connected by a glass tube to a beaker of water positioned below the flask. As the gas dissolves in the water, water from the beaker is pulled up through the glass tube creating a fountain effect. Phenolphthalein is added to the water in the beaker so that as the water enters the round-bottomed flask it turns pink from the ammonia.
Ammonia gas is very water-soluble. Ammonia is a base.
A film of nylon is formed at the interface between two immiscible liquids. When the film is lifted from the container, it is continually replaced forming a rope of Nylon.
Nylon is a synthetic polymer. Nylons are polyamides made form the reactions of diacids and diamines.
Show examples of common synthetic organic polymers to encourage thought / discussion about differences.
Show examples of common synthetic organic polymers to encourage thought / discussion about differences.
Two chemicals from a foam polymer floatation kit are mixed together to produce a polyurethane foam which eventually hardens.
The polyurethane foam is produced through a co-polymerization reaction between the two chemicals. The foaming results because the solvent for the Freon is used up as the reaction proceeds; the Freon goes into gas bubbles which are trapped in the polymer.
The calcium carbide lamp of a Caving Helmet is shown and demonstrated.
Water and calcium carbide react to produce acetylene gas which can be used to light a lamp on a caving helmet.
A copper wire coil in a Christmas tree shape is allowed to sit in a solution of silver nitrate. Within an hour silver metal needles form on the wire.
Copper metal is oxidized by the Ag1+ to Cu2+ and the Ag1+ ions are reduced by the copper metal to silver metal.
Zinc and copper cells has been constructed so that a person can conduct the electricity moving through the cell. More appropriate for a laboratory situation where students can participate, but can be used in lecture for students to 'play' with after class or to use as an in class experiment to stimulate discussion about electricity. Some people will conduct more electricity than others.
The human body conducts electricity. The spontaneous flow of electrons from zinc to copper is electricit
When a nail (Fe) is dipped into a copper sulfate solution, copper metal is plated onto the nail. When a piece of copper is dipped into a ferric sulfate solution, no reaction is observed.
The reaction between iron metal and copper (II) is an oxidation-reduction reaction. Iron is above copper on the activity series. It loses electrons more easily than Cu in aqueous solution. Cu metal will not lose its electrons to Iron (II).
Water is decomposed into hydrogen and oxygen gases using electricity. A Hoffman electrolysis apparatus collects the two gases separately and shows the 2 to 1 ratio nicely. If a pH indicator is used the anode becomes yellow and cathode becomes blue. Hydrogen gas can be burned to produce a small pop sound and the oxygen can be used to re-ignite a glowing wooden splint.
When a DC current is passed though an aqueous sodium sulfate solution, water is oxidized at the anode producing O2 and reduced at the cathode producing H2. The solution becomes acidic at the anode and basic at the cathode.
Copper metal is electroplated onto a nickel rod. Nickel rod takes on a copper sheen. The wires connected to the electrodes are switched and the copper sheen on the nickel disappears.
Using electricity, Cu2+ cations are reduced to copper metal which plates onto another metal. Also the Cu0 metal can be oxidized back to Cu2+ cations.
A Gummi Bear is dropped into a test tube of heated potassium chlorate. The Gummi Bear is combusted.
Exothermic reactions produce a lot of heat. Potassium Chlorate is a strong oxidizing agent; a fire may start when it is mixed with combustible materials.
A U tube is used to construct a Cu-Zn battery. The concentration of the Cu and/or Zn solution is varied and the emf is measured to show that it varys with concentraion.
The emf of a cell depends on the concentrations of ion and on gas pressures. Nernst equation relates the cell emf's for various concentrations and gas pressures to standard electrode potentials.
The energy from a series of zinc and copper electrodes through five oranges is used to charge a capacitor, which is then used to light a flash bulb.
Oranges conduct electricity. The spontaneous flow of electrons from zinc to copper is electricity and can be used to do some work.
A manganese (II) solution and manganese (VII) solutions are mixed. Brown solid MnO2 precipitates as a result of formation of Manganese (IV).
In this reaction manganese (IV) acts as oxidation agent for manganese (II).
A battery is constructed using zinc and copper electrodes.
The spontaneous flow of electrons from zinc to copper is electricity.
Induced by the touch of an iron nail, gallium metal appears to take on a life of its own as it continuously oscillates between a dull flat puddle and a shiny sphere.
Electrons from a corroding anode (iron nail) are transferred to Ga3+, forming gallium metal. The gallium metal is spherical in shape due to its surface tension. Dichromate oxides the surface of the gallium, creating Ga3+ and breaking the surface tension in the gallium metal. This oscillation continues for about 30 minutes as the dichromate concentration gradually decreases.
A bottle containing a colorless solution is shaken and instantly turns blue. The blue bottle is left to sit for a few minutes and returns to a colorless state. If shaken again, the bottle will again become blue.
In the presence of OH-, glucose is converted to gluconic acid. This reaction provides H+ and 2e-, which act to convert methylene blue from it’s oxidized (blue) form to it’s reduced (colorless) form. When the bottle is shaken, O2 from the upper portion of the bottle is associated into the solution. This causes an oxidation of the reduced form of methylene blue, re-creating the blue color. If left to sit, the O2 will come out of solution and the reduced form of methylene blue will be re-created.
A solar cell receives light from a lamp and supplies power to a fuel cell. The fuel cell converts liquid water into hydrogen and oxygen gas, which is stored in separate compartments. When a switch is flipped, the fuel cell works in reverse, converting this stored hydrogen and oxygen back into water. In the process, a current is created and routed to a motor, which is used to power a toy car.
In order to break water down into its component gases, an electrical current must be passed through it. This process is called electrolysis.
An endothermic reaction lowers temperature in flask so that the flask will freeze and stick to a wet piece of wood. An endothermic reaction is used in drug store instant cold pack. An exothermic reaction in a Styrofoam cup will significantly raise the temperature in the cup.
Some chemical reactions absorb heat from the surroundings, resulting in a cooling of the surroundings (Endothermic Reactions). Some chemical reactions evolve heat, resulting in a warming of the surroundings (Exothermic Reactions).
When two clear solutions (one blue and one colorless) are mixed together they generate light. The resulting solution has a bluish glow. It is nicely displayed by running it through a spiraling tube.
Chemical energy can be converted in to other forms of energy – sometimes it is converted to heat (exothermic reactions), electricity (batteries), and sometimes into light.
Four different metal rods (lead, iron, copper, and aluminum) are heated and then placed on a block of paraffin wax.
Depending on the specific heat of the metal, the different metals will be able to melt more or less paraffin wax.
A small chunk of phosphorus is ignited by flame and quickly plunged into a flask containing oxygen gas. The resulting reaction produces heat, smoke and a spectacular bright light that last for 5-10 seconds.
Finely dispersed phosphorus will readily ignite in the presence of oxygen at room temperature and must be stored under water or in a solvent such as carbon disulfide.
About 30 seconds after the acid is added to the sugar, a column of black carbon grows up from the beaker. There are vapors and the smell of burned sugar.
Sulfuric acid is a strong acid and has a strong affinity for water.
The blowers in the Collisions Cube are set at low power on each side. The side with the ping-pong balls is said to represent reactants, while the empty side is said to represent products. The power should be low enough so that no ping-pong balls change sides. The hole at the top is representative of the energy barrier that reactant molecules must overcome in order for the reaction to proceed. The students are asked to propose a change to the system that would allow for product creation.
Product creation is sometimes limited by the amount of activation energy provided.
A Gummi Bear is dropped into a test tube of heated potassium chlorate. The Gummi Bear is combusted.
Exothermic reactions produce a lot of heat. Potassium Chlorate is a strong oxidizing agent; a fire may start when it is mixed with combustible materials.
Sulfuric acid is added to 0° C water in one beaker and 0° C ice in another. The temperature in the beaker of water increases and the temperature in the beaker of ice decreases.
Heat is released when acid reacts with water causing the temperature of the water to increase. However if the water is frozen initially the heat from this reaction is absorbed by the phase change of the ice molecules to liquid water. Additionally, the temperature of this water will decrease due to the freezing point depression effect of the solute (the acid).
Water is added to NaCl and the temperature decreases by about 3°C; water is added to KNO<sub>3</sub> and the temperature decreases by about 12°C; water is added to LiCl and the temperature increases by about 70°C.
Heats of solution can be exothermic and endothermic.
A flask with a volume of 1 Liter is evacuated. In class the evacuated flask is set on a balance and weighed. Air is let into the flask. The flask with air is then weighed.
Density = mass / unit volume
Vapors of ammonia and hydrochloric acid diffuse towards each other inside a tube. A ring of ammonium chloride forms where the two chemicals meet and react.
The ratio of diffusion rates of two gases is equal to the square root of the inverse of the ratio of their molecular weights.
There is a "Boyle's Law Unit" that consists of a large syringe connected to a pressure gauge on a clear plastic stage that is meant to be viewed through an overhead projector. As the syringe is used to increase or decrease the volume of air in the syringe, the pressure gauge shows a decrease or increase in pressure. Also the 'Unit' includes a bulb that can be emmersed in boiling water, ice bath, and liquid nitrogen to show the relationship between temperature and pressure and to extrapolate to absolute zero.
Boyle's Law: PV = k
When bromine is let into an evacuated flask, the vapor quickly moves into the flask. When bromine is let into a flask containing air, the vapor only very slowly diffuses into the flask.
The speed at which bromine diffuses into a flask is slowed in the presence of O2.
Water is added to an empty soda-pop can and heated to boiling. Can is then quickly inverted into cold water which causes it to collapse. Or a larger gas can is used and instead of being inverted into the water after heating the water inside, the can is stoppered and then allowed to cool in water or in room temperature air.
When water vapor inside the can is cooled it condenses, decreasing the pressure on the inside of the can. With the atmospheric pressure on the outside of the can greater than that on the inside, the can will collapse.
Various objects are frozen and then smashed and shattered. A balloon filled with air will shrink when dipped in liquid nitrogen.
Liquid nitrogen is very cold (it boils at -195.79° C). The volume of a gas will decrease as its temperature decreases.
A beaker is completely filled with water, a piece of cardboard is set on top of the beaker, and the beaker is turned upside down. The cardboard stays on (under) the beaker holding the water inside the beaker.
The pressure of the water on the cardboard is less than the pressure of the air on the cardboard.
Food color spreads out more quickly through a bowl of warm water then it does through a bowl of cold water.
The rate of diffusion of water and food color molecules is increased when temperature is increased. Temperature is a measure of molecular motion.
A balloon expands as it is filled with CO2 gas that sublimes from CO2 solid. A balloon filled with CO2 gas contracts (appears to deflate) when it is set on a dewar of liquid nitrogen.
The volume of CO2 increases as it changes from solid to gas.
A four sided frame mounted on a glass plate with a motor to vibrate the frame is set on an overhead projector. Small balls inside the frame are agitated by the vibration of the frame.
The kinetic theory assumes that all matter is composed of invisibly small particles that are always in motion. Gases are thought to consist of a collection of molecules moving and colliding at high speed, similar to a collection of rapidly moving marbles. The physical behavior of gases is then explained by applying the demonstrated theories about motion and collision which apply to larger, visible object
When one side of a pulse bulb is held, the red liquid inside magically moves to the side that is not held.
Heat from a hand is sufficient to cause the gas above the liquid to exert enough pressure to move the liquid to the other side of the apparatus.
Several different objects and materials will expand inside a vacuum chamber when a pump is allowed to draw air from inside.
The volume of a gas can increase when the pressure exerted on it is decreased. Each object has air pockets full of gases that will expand inside a vacuum.
A beaker containing water and a thermometer is boiled at room temperature inside a vacuum chamber. The temperature gradually drops as the water boils until the water solidifies (sometimes demonstrating the triple point).
Boiling point is the temperature at which the vapor pressure of a liquid equals atmospheric pressure. If the pressure around a beaker of water is reduced to nearly zero, boiling can occur at room temperature.
A small amount of water is squirted into an inverted round-bottomed flask full of ammonia gas. This flask is connected by a glass tube to a beaker of water positioned below the flask. As the gas dissolves in the water, water from the beaker is pulled up through the glass tube creating a fountain effect. Phenolphthalein is added to the water in the beaker so that as the water enters the round-bottomed flask it turns pink from the ammonia.
Ammonia gas is very water-soluble. Ammonia is a base.
Spectacular colors are produced as various balloons are ignited.
As the hydrogen is combusted, electrons in metal salts concealed within the balloons are excited to higher energy levels. As the electrons fall back to lower energy levels, photons are emitted. The color of the burst will depend on the metal salt used and the corresponding wavelength of light emitted.
For Version 1, a faucet-like contraption drips bubbles filled with CO2 fog. For Version 2, CO2 gas is poured down a Plexiglas staircase. Candles on the individual stairs are extinguished on at a time.
Balloons containing helium, oxygen and carbon dioxide are submerged in liquid nitrogen. The helium remains in the gas phase, the oxygen becomes a liquid and the carbon dioxide becomes a solid.
When molecular motion is slowed down, the state of matter of an element changes.
When the blowers of the Collisions Cube are provided with a little power, the ping-pong balls will begin to hover, representing the presence of a vapor. The students should be pointed to the equilibrium that exists between this vapor phase and the liquid phase that lies below.
The difference between states of matter lies in how quickly the molecules of a substance are moving.
Boyle's law can be demonstrated (PV = constant) by showing the Collisions Cuve in two different arrangements.
Boyle's Law: PV = k
Sulfuric acid is added to 0° C water in one beaker and 0° C ice in another. The temperature in the beaker of water increases and the temperature in the beaker of ice decreases.
Heat is released when acid reacts with water causing the temperature of the water to increase. However if the water is frozen initially the heat from this reaction is absorbed by the phase change of the ice molecules to liquid water. Additionally, the temperature of this water will decrease due to the freezing point depression effect of the solute (the acid).
A pressure chamber containing liquid sulfur hexafluoride is warmed to the critical temperature of the SF6. A camera is aimed at a window in the chamber and students can watch as the boundary between the liquid and gaseous phases blurs and eventually disappears.
Critical temperature is the temperature above which there is no distinction between the liquid phase and vapor phase of a substance.
A small magnet in the shape of a cube levitates above a small black disk.
Superconductors 'exclude' the magnetic field of a magnet.
Ice cubes and a cube of frozen deuterium oxide are dropped into beakers containing distilled water. After the hygroscopic D2O cube has lost its outer coating of H2O, it will sink. The regular ice cubes will remain floating on top of the liquid H2O.
When water freezes the structure expands so that the solid water is less dense than the liquid form. This is not the case for mostly all other substances. Deuterium oxide should sink in a container of water, since it contains a heavier isotope of Hydrogen.
Two ball bearings are dropped from the same height, down identical plastic tubes onto two different surfaces: one stainless steel, and the other an amorphous metal called Liquidmetal®. The ball bounces much longer on the amorphous metal surface, indicating a much different energy transfer interaction than that of the stainless steel base.
The atoms in an amorphous material are not arranged in any ordered structure, rather they have a tightly-packed, but random arrangement. Amorphous materials are formed by cooling the liquid material quickly enough to prevent crystallization; the atoms do not have time to arrange themselves into an ordered structure.
Two equal mass, nearly equal density black balls are dropped from the same height. One ball will bounce and the other will hit the ground with a thud and stop. The balls can be heated in a hot water bath or cooled down in dry ice to see the result on the bouncing ability.
The balls are made of different polymers that have different coefficients of restitution. When heated in boiling water, the sad ball will become more elastic and bounce as high as 1/3rd the height of the happy ball. Both balls will have less bounce if cooled off in dry ice.
A piece of tile from the original construction of space shuttle Columbia is thrust into a torch flame. The tile will glow red in a matter of seconds. The tile can be held by bare hands 20-30 second later.
The material has a low specific heat and a low thermal conductivity. A material of this type is necessary for a space shuttle’s reentry, as the friction caused by passing through an enormous quantity of air in a short time produces a great amount of heat.
A cup is filled with water from a tap and set it down on a tray. Hundreds of paperclips are put into the cup without the water inside it spilling out. Once the surface of the water has bowed to a maximum, a drop of soap is touched to the surface with a toothpick, causing the surface tension to instantly break and the water to spill onto the tray. Alternatively, a large beaker is filled about 3/4ths of the way with water. Sulfur that is sprinkled onto the surface of the water floats due to the surface tension. Soap is then added to break the surface tension in the water, causing the sulfur to fall to the bottom of the beaker.
A majority of the water molecules contained within the beaker or cup are experiencing intermolecular forces from all directions and are relatively low in energy when compared to the molecules at the surface, which are only experiencing these forces from below and from neighboring surface molecules. Since most water molecules would prefer to be lower in energy (and remain with the bulk of the liquid), the surface will take on a spherical shape, demonstrating a minimization of the ratio of surface area to volume. These surface molecules form an elastic-like barrier that can support some lighter objects. When we add soap to water, we disrupt the intermolecular forces between water molecules, breaking the surface tension.
When the blowers of the Collisions Cube are provided with a little power, the ping-pong balls will begin to hover, representing the presence of a vapor. The students should be pointed to the equilibrium that exists between this vapor phase and the liquid phase that lies below.
The difference between states of matter lies in how quickly the molecules of a substance are moving.
A straight strip containing a thin layer of two different metals bends when heat is applied. The strip will bend in the other direction when it is chilled in ice water.
Solid Expansion, Dispersal of Matter
Description: Na and Mg metals react with oxygen to produce basic oxides that turn universal indicator purple (basic). Carbon on the other hand reacts with oxygen to produce an acidic oxide that turns universal indicator orange (acidic).
Concept: Most metals react with oxygen to produce basic oxides. Most non-metals react with oxygen to produce acidic oxides.
Lithium, sodium, and potassium metals are sliced and then a small sample of each is reacted with water.
The alkali metals are soft and silvery. They are also the most reactive metals having the lowest ionization energies. They react readily with water, lithium being the least reactive and potassium the most.
Samples of Mg and Ca are displayed. Mg and HCl produce less bubbles than Ca and HCl. Mg and H2O produces less hydroxide and therefore less pink with phenolphthalien than Ca and H2O.
The alkaline earth metals are less reactive and harder compared to the alkali metals. They do not react as readily with water. Mg is less reactive than Ca.
Many samples of elements are available to be displayed in class.
An element is a substance that cannot be decomposed by any chemical reaction into simpler substances; a type of matter composed of only one kind of atom, each atom of a given kind having the same properties.
Small cards showing each element and their atomic number are arranged to form the periodic table.
When the elements are arranged by atomic number, their physical and chemical properties such as atomic radius, ionization energy and electron affinity, vary periodically.
Water is decomposed into hydrogen and oxygen gases using electricity. A Hoffman electrolysis apparatus collects the two gases separately and shows the 2 to 1 ratio nicely. If a pH indicator is used the anode becomes yellow and cathode becomes blue. Hydrogen gas can be burned to produce a small pop sound and the oxygen can be used to re-ignite a glowing wooden splint.
When a DC current is passed though an aqueous sodium sulfate solution, water is oxidized at the anode producing O2 and reduced at the cathode producing H2. The solution becomes acidic at the anode and basic at the cathode.
He, Ne, and Ar discharge tubes show different colors.
The electrons of an element are excited in a discharge tube. As these excited electrons fall back from one energy level to another, they will emit photons of light. These photons will have different colors depending on the element and its discrete energy levels. That is, different wavelengths of light (colors) will be emitted when the electrons of different elements go down the steps between their energy levels. Each element will have its own set of steps, therefore each will have its own color or set of colors.
Samples of Cl2 gas, Br2 liquid, and I2 solid are displayed in round 1 L glass bulbs.
When excited, electrons of different halogens emit different colors.
Different salts are burned within glass Petri dishes. Sodium burns orange, potassium - purple/blue, barium - green, copper – blue/green, and lithium or strontium – red
When an element is burned, the electrons will be excited. Then as these electrons fall back from one energy level to another, they will emit photons of light. These photons will have different colors depending on the element and its discrete energy levels.
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A 'bathtub ring' is created in the classroom.
The effect of hard water (water that contains Ca 2+ and Mg 2+) on soap. More soap is necessary for sudsing in hard water than in soft water. Commercial dish washing detergent on the other hand produces suds easily, even in hard water.
Molecular models are displayed.
Compounds formed by elements are structured in different ways.
A light bulb will glow when a substance that conducts electricity is inserted in a break in the wires that leads to and from the power source.
Solutions that contain ionic compounds conduct electricity. The more a compound separates into its ionic units, the more ions there are in solution. The more ions there are, the more electricity that flows through the solution. For example, the acetic acid will light the bulb dimly and the hydrochloric acid will light the bulb more brightly due to its higher Ka value.
Molecular models are displayed.
Compounds formed by elements are structured in different ways.
Balloons containing helium, oxygen and carbon dioxide are submerged in liquid nitrogen. The helium remains in the gas phase, the oxygen becomes a liquid and the carbon dioxide becomes a solid.
When molecular motion is slowed down, the state of matter of an element changes.
Small pieces of a note card that have been covered on one side with graphite from a pencil are allowed to fall in between a layer of water and hexane. Initially, some of the note card pieces will face graphite side up, while others will remain graphite side down. After shaking, most, if not all of the pieces will orient themselves so that the graphite-covered side faces toward the upper hexane layer.
The graphite on the notecard will prefer to face the non polar hexane layer, while the cellulose on the uncoated side will prefer to face the water layer.
A color-coded, 3-dimensional model is used to explain why DNA must take on a helical shape.
The base pairs essentially stack on top of one another, and are held together by dispersion forces. However, the phosphate groups connecting these base pairs will repel one another due to their excess negative charge. One may expect the base pairs to separate because of this repulsion between phosphate groups. However, a lower energy alternative to the base pairs separating is for the phosphate groups to position themselves in a staggered arrangement, with the base pairs maintaining their stacked positions. It is this staggering of the phosphate groups that leads to the helical shape of DNA.
When the blowers of the Collisions Cube are provided with a little power, the ping-pong balls will begin to hover, representing the presence of a vapor. The students should be pointed to the equilibrium that exists between this vapor phase and the liquid phase that lies below.
The difference between states of matter lies in how quickly the molecules of a substance are moving.
A flask with a volume of 1 Liter is evacuated. In class the evacuated flask is set on a balance and weighed. Air is let into the flask. The flask with air is then weighed.
Density = mass / unit volume
Students are asked to volunteer to measure the width of the lecture hall using meter sticks. Data is pooled and the mean and standard deviation is calculated.
The number of significant figures in a measurement is related to the precision of the measurement.
One kilogram and 100 g samples are displayed to compare their sizes. A liter beaker is displayed to show its size. One mole samples of various elements and compounds are displayed. One mole of NaCl and 1 Liter beaker are shown in relationship together to demonstrate molarity.
A mole is not a measurement of a static amount of material.
The temperature of an ice bath is measured while salt is dissolving in it. This is compared to the temperature of a saturated salt solution/ice mixture and the Celcius temperature is calculated to be 0 degrees F.
In attempting to produce as cold a temperature as possible, Fahrenheit prepared an ice bath to which he added salt to lower the temperature further. He assigned a value of zero to that temperature.
Five different white powders are reacted with various substances. An unknown powder that is one of the five, is reacted with the same substances. These results are used to identify the unknown.
Qualitative observations of reactions are used to identify unknown substances.
Nine blocks, all 1.0 inches in size, are compared in several manners to find their relative and absolute densities.
The density of a substance relates to how closely the atoms within that substance are packed. When comparing substances equal in size (volume) the more dense substances should have a larger mass.
A Geiger counter is used to demonstrate differences in the amount of radioactivity of various sources, including an antique fiestaware plate. Radiation can be blocked by paper, wood, or lead depending on the source. The counter has analog gauge, red flashing light, and sound to indicate radiation. A microphone helps to make the sound more audible to students in large lecture hall.
Emission of alpha, beta, and gamma radiation can be detected by a Geiger counter. Alpha particles can be blocked with paper, whereas a lead brick is required to block gamma photons.
Several samples of alkanes are displayed.
The physical properties of the alkanes are related to their molecular structure.
Tollen’s Reagent is added to two flasks. A dextrose water solution is added to one and swirled. The contents of the flask turn brown and then silver is plated onto the inside of the flask. Sucrose is added to the other flask. The contents may turn brown but no silver is plated.
Silver (I) is reduced to silver metal by aldehydes but not by ketones.
A film of nylon is formed at the interface between two immiscible liquids. When the film is lifted from the container, it is continually replaced forming a rope of Nylon.
Nylon is a synthetic polymer. Nylons are polyamides made form the reactions of diacids and diamines.
Show examples of common synthetic organic polymers to encourage thought / discussion about differences.
Show examples of common synthetic organic polymers to encourage thought / discussion about differences.
Two chemicals from a foam polymer floatation kit are mixed together to produce a polyurethane foam which eventually hardens.
The polyurethane foam is produced through a co-polymerization reaction between the two chemicals. The foaming results because the solvent for the Freon is used up as the reaction proceeds; the Freon goes into gas bubbles which are trapped in the polymer.
The calcium carbide lamp of a Caving Helmet is shown and demonstrated.
Water and calcium carbide react to produce acetylene gas which can be used to light a lamp on a caving helmet.
Two equal mass, nearly equal density black balls are dropped from the same height. One ball will bounce and the other will hit the ground with a thud and stop. The balls can be heated in a hot water bath or cooled down in dry ice to see the result on the bouncing ability.
The balls are made of different polymers that have different coefficients of restitution. When heated in boiling water, the sad ball will become more elastic and bounce as high as 1/3rd the height of the happy ball. Both balls will have less bounce if cooled off in dry ice.
A 'bathtub ring' is created in the classroom.
The effect of hard water (water that contains Ca 2+ and Mg 2+) on soap. More soap is necessary for sudsing in hard water than in soft water. Commercial dish washing detergent on the other hand produces suds easily, even in hard water.
A color-coded, 3-dimensional model is used to explain why DNA must take on a helical shape.
The base pairs essentially stack on top of one another, and are held together by dispersion forces. However, the phosphate groups connecting these base pairs will repel one another due to their excess negative charge. One may expect the base pairs to separate because of this repulsion between phosphate groups. However, a lower energy alternative to the base pairs separating is for the phosphate groups to position themselves in a staggered arrangement, with the base pairs maintaining their stacked positions. It is this staggering of the phosphate groups that leads to the helical shape of DNA.
When a yellow solution, K2CrO7, is added to three different alcohols, the solution turns blue in two of the alcohols and remains yellow in one.
Potassium dichromate will oxidize propyl alcohol and sec-butyl alcohol, but not tert-butyl alcohol. Primary and secondary alcohols are easily oxidized. The carbons holding the OH groups in propyl and sec-butyl alcohol are also holding at least one hydrogen. This hydrogen is removed by the oxidizing agent along with the H from the hydroxyl group leaving a carbonyl group and forming water.
Samples of various odorivectors can be passed around for the students to smell.
There is a relationship between structure of a molecule and its odor. Humans sense of smell depends on a lock and key mechanism. If a person lacks the lock for a particular odor, they will be unable to sense it.
Sugar is used to rotate the plane of polarized light.
The structure of fructose is such that when polarized light passes through an aqueous solution of the sugar, the light is rotated counter clockwise. Dextrose will rotate the polarized light clockwise.
Models are used to illustrate secondary protein structure.
Peptide chains tend to form orderly hydrogen-bonded arrangements.
An oleic acid (unsaturated) and lauric acid (saturated) solution is displayed on an overhead projector.
The addition of IBr to the lauric acid shows no change, while the oleic acid solution grows gradually paler as its double bonds take on bromine.
A blue, water-soluble indicator is added to a separatory funnel containing a layer of H2O and a layer of CHCl3. Acid is added to the blue aqueous layer, and the color changes from blue to red. After shaking, some of the red color (the protonated, organic soluble version of the blue indicator) moves into the bottom layer. After thorough mixing, the red exists solely in the organic layer. The extraction can then be done in reverse by addition of a base.
The protonation of a water soluble indicator makes a neutral compound that is soluble only in organics.
A student is asked to help initiate a 'chemical reaction' by stirring two components together. They quickly add water to the super absorbent polymer and begin stirring. They soon find out that it is almost impossible to stir the gel that has quickly formed. Alternatively, three 'empty' mugs are shown to the students. A large amount of water is added to one of the mugs from a faucet, and the three mugs are shuffled repeatedly. The demonstrator then begins to dump it on three student's heads. To their surprise, none the mugs spill water. The students are then shown the gel that has formed in the mug containing the super absorbent polymer.
Sodium polyacrylate can absorb 300-5000 times its weight in pure water. As a dry powder, the polymer is coiled. When water is added, the cross-linked chains expand.
A full, peeled carrot is submerged into bromine water and left to sit for most of the class period. When the carrot is pulled out and sliced or compared to a normal carrot, an obvious discoloration can be seen.
The orange color in carrots can be attributed to the presence of beta-carotene. As a result, we observe reflected, orange light when we see a carrot. Adding bromine across the multiple double bonds in beta-carotene disrupts this conjugation and the color of the carrot gradually disappears.
A solution of t-butyl chloride in acetone is added to water in the presence of a base and universal indicator. Depending on the concentration of t-butyl chloride, the reaction to form t-butyl alcohol is indicated by a series of drastic color changes.
The color change occurs as aqueous chlorine removes a proton from the transition state, resulting in a lower pH of the system (see mechanism in “concept” section). This demonstration can also qualitatively show that the rate of reaction is dependant of the concentration of t-butyl chloride.
Four dishes are displayed on an overhead projector, each containing egg white. The dishes are labeled according to the method that will be used to denature the albumin contained within the egg white. The egg whites take on an opaque appearance when the albumin is denatured, and dark spots will appear on the projected images.
Denaturation is the disruption of secondary and tertiary protein structure resulting in the insolubility of that particular protein. In their water-soluble state, proteins exist in a globular form, with hydrophilic regions on the outside and hydrophobic regions contained within the globule. When proteins become denatured, some outside force acts to make the globule more linear, exposing the hydrophobic regions to the water.
A model has been constructed to demonstrate the Sn2 reaction mechanism.
The model shows the initial tetrahedral arrangement around the central atom, the trigonal bipyramidal transition state when both nucleophiles are attached and the resulting inversion in configuration around the central atom when the new nucleophile is attached.
Aspirin is used to create wintergreen oil. The esterification can be performed in about 5 minutes, and the product can be passed around the class for students to smell. As an optional addition, iron (III) chloride can be added to the product to indicate the presence of a phenol.
Using concentrated sulfuric acid as a catalyst, acetylsalicylic acid (aspirin) is converted to methyl salicylate (wintergreen oil). Although the reaction will not have time to reach equilibrium after only 5 minutes of reflux in a test tube, enough methyl salicylate will have been produced for students to detect the smell.
Eight different alkyl halides are tested with silver nitrate and sodium iodide solutions, and their relative reactivities are observed.
Alkyl halids undergo SN1 or SN2 substitution reactions epending on conditions.
A TLC plate containing fingerprint residue is dipped into a solution containing ninhydrin. The plate is heated to reveal the burgundy-colored mark of a distinguishable fingerprint.
Ninhydrin will react with the amino acids in fingerprint residue. Thermal decomposition creates an aldehyde containing the R group from the amino acid and carbon dioxide. The amine reacts with another ninhydrin molecule to produce the burgundy-colored molecules.
Cotton or dryer lint that has been dissolved in aqueous [Cu(NH3)4(OH)2] is injected from a medicine dropper into 3M H2SO4. The result is a thread of rayon.
A saturated solution of copper (II) carbonate in concentrated ammonium hydroxide will dissolve cellulose. The cellulose polymer is regenerated as extruded fibers when the complex is reprotonated below the surface of the sulfuric acid. The polymer prepared is referred to as cuprammonium rayon, and is an example of regenerated cellulose. Regenerated cellulose is usually less crystalline than natural cellulose
A Borax solution is mixed with a solution of white glue. The result is a rubbery substance with very unique properties.
White glue contains polyvinyl alcohol. When mixed with water, this polyvinyl alcohol dissolves. Borax acts as a crosslinking agent when added to this glue solution, creating a new, rubbery polymer.
The Collisions Cube is set up with mixture of two substances with differing boiling points (white balls and red balls weighted with pennies) on one side of the divider that contains a hole near the top. The hole in the divider is said to represent a condenser.
The mixture will begin to evaporate, with a majority of the white balls reaching heights greater than the heights reached by the red balls.
One kilogram and 100 g samples are displayed to compare their sizes. A liter beaker is displayed to show its size. One mole samples of various elements and compounds are displayed. One mole of NaCl and 1 Liter beaker are shown in relationship together to demonstrate molarity.
A mole is not a measurement of a static amount of material.
A few students are given a piece of Bazooka bubble gum that has been pre-weighed and asked to chew the gum for about 20 minutes. After 20 minutes the pieces of gum are weighed again.
The molar mass (molecular weight) of sugar (sucrose) is large, 342.30 g/mol.
Balls in plastic bags represent atoms in molecules. Shuffling balls into different bags represent a reaction. The number and color of the balls does not change.
The atoms in a chemical reaction are conserved and chemical equations can be balanced.
Four balloons are filled with gas mixtures of CH4 and O2: one with pure O2, one with pure CH4, one with 2 CH4 / O2, and one with 1 CH4 / 2 O2. They are successively ignited with a burner. Only the balloon with the correct stoichiometric mixture will detonate.
CH4 is a flammable. The combustion reaction efficiency of CH4 and O2 depends on stoichiometry. Also, this reaction is slow at room temperature. The heat of the flame speeds up this reaction.
A bottle has two nails poking inside such that the points of the nails almost touch. A couple mL of methanol are put in the bottle and the bottle is corked and gently shaken and then clamped to a ring stand. A tesla coil is applied to the head of one of the nails. Almost immediately the methanol is ignited and the cork is shot into the air. Quickly the instructor corks the bottle. The bottle is shaken and the tesla coil is applied, but nothing happens. Why not? Then the instructor blows into the bottle, shakes, and uses the tesla coil to once again shoot the cork. Why does it work again?
Oxygen is required for the combustion of methanol. Also molecules in the vapor phase are farther apart than in the liquid phase and present more surface area for reaction.
A candle in lit and a jar is placed over it. Within a couple minutes the flame will extinguish due to lack of oxygen (the limiting reagent in this case).
A limiting reagent is defined as a reagent that will completely halt a reaction when it runs out.
One kilogram and 100 g samples are displayed to compare their sizes. A liter beaker is displayed to show its size. One mole samples of various elements and compounds are displayed. One mole of NaCl and 1 Liter beaker are shown in relationship together to demonstrate molarity.
A mole is not a measurement of a static amount of material.
A crystallizing dish with an eye drawn on the bottom surface is placed on an overhead projector. Egg white is put into the dish, and when acid is added, the egg white clouds up to simulate what an acid would do to one’s eye. Sodium bicarbonate is dropped onto the spots where acid has been added to simulate what happens when someone tries to “undo” the damage that acid causes.
The egg white is transparent and made up of protein just like the layer over our eye. When the acid is added, these proteins (albumin in the egg) are denatured. Adding sodium bicarbonate solution cannot undo the damage. The proteins cannot be rebuilt.
Green food coloring (a mixture of food dyes Blue 1 and Yellow 5) is separated into its components using a C18 Sep Pak and various mixtures of methanol and water.
A nonpolar stationary phase is used for reverse-phase chromatography. The material contained in the Sep Pak cartridge is relatively nonpolar, and will retain other nonpolar molecules.
A pickle is placed into a light socket and a tungsten electrode is put through the top. The lights are turned low and current is sent arcing through the pickle from a variac that had been plugged into a wall outlet. The pickle glows brightly for a few seconds and eventually starts to smoke.
The pickling process involves soaking a cucumber in a concentrated salt solution (or brine). Water flows out of the cucumber and salt flows into the cucumber, creating a salty, dehydrated cucumber (or pickle). The inside of the pickle is essentially an electrolyte solution, and conducts electricity.
A light bulb will glow when a substance that conducts electricity is inserted in a break in the wires that leads to and from the power source.
Solutions that contain ionic compounds conduct electricity. The more a compound separates into its ionic units, the more ions there are in solution. The more ions there are, the more electricity that flows through the solution. For example, the acetic acid will light the bulb dimly and the hydrochloric acid will light the bulb more brightly due to its higher Ka value.
Small pieces of a note card that have been covered on one side with graphite from a pencil are allowed to fall in between a layer of water and hexane. Initially, some of the note card pieces will face graphite side up, while others will remain graphite side down. After shaking, most, if not all of the pieces will orient themselves so that the graphite-covered side faces toward the upper hexane layer.
The graphite on the notecard will prefer to face the non polar hexane layer, while the cellulose on the uncoated side will prefer to face the water layer.
Water is added to NaCl and the temperature decreases by about 3°C; water is added to KNO<sub>3</sub> and the temperature decreases by about 12°C; water is added to LiCl and the temperature increases by about 70°C.
Heats of solution can be exothermic and endothermic.
Ethanol is miscible in water. There is a phase boundary between n-butanol and water.
As the carbon chains of alcohol become longer, alcohol becomes less polar and more hydrophobic.
1) A supersaturated solution of sodium acetate is poured onto a watch glass that contains some dry sodium acetate crystals. When the solution hits the crystals it recrystalizes to form a column up into the beaker. 2) As a saturated Cupric Sulfate solution cools beautiful crystals form.
A supersturated solution contains more dissolved substance than a saturated solution. Supersaturated solutions are not in equilibrium with the solid substance. A saturated solution is one that is in equilibrium with respect to the dissolved substance. This equilibrium changes with temperature.
A beam of light is projected through a fish tank onto a screen. The fish tank contains a sodium thiosulfate solution which reacts with sulfuric acid to gradually produce particles of sulfur. As particles gradually accumulate they scatter the light and gradually produce blue, yellow, and then red colors on the screen, simulating a sunset.
Particles in the atmosphere scatter the light from the sun to produce blue sky and red sunsets.
Several small cardboard disks that are white on one side and colored with graphite (pencil 'lead') on the other are put into a jar containing hexanes and water. The jar is shaken and when the hexane and water layers separate, the disks settle at the interface between the two layers. The mysterious thing is that the gray sides of the disks always end up facing up.
Graphite is nonpolar carbon which associates with the nonpolar hexanes. The cellulose in the exposed paper contains polar regions that are attracted to the polar water.
A dialysis tube full of a starch solution is immersed into a solution of tincture of iodine. Tincture of iodine is dropped into a beaker of starch solution and the starch solution turns purplish-black. After about 30 minutes the starch solution in the tubing is turning purple. In about a day it is completely purplish-black.
Osmosis is the movement of a substance across a semi-permeable membrane from an area that is more concentrated in that substance to an area that is less concentrated. Semi-permeable membranes only allow certain substances through.
A penny is boiled in a solution of NaOH on top of Zn metal and the color of the penny turns silver in about 45 seconds. The penny is held in the flame of a burner for a few seconds and it turns golden.
Granular zinc dissolves in NaOH to form [Zn(OH)<sub>4</sub>]<sup>-2</sup>. This zincate ion becomes reduced to metallic zinc on the surface of a copper penny. Zinc and copper when heated in a flame form brass.
Dish soap is added to two similar looking bottles: one contains water, while the other contains a 5% solution of calcium chloride. The bottles are both shaken vigorously. The bottle containing the water retains its transparency, while the bottle containing calcium chloride is clouded by the insoluble soap scum formed.
Soap molecules are salts of carboxylic acids with long hydrocarbon chains. Soap is normally made from sodium or potassium salts which are soluble in water. When the carboxylate anions from the salts combine with certain ions, such as calcium, they become insoluble and form a precipitate commonly referred to as soap scum.
A stripe of red palm oil (or another colored, greasy substance) is painted onto two cloth canvases. Sponges are used to try and remove the greasy substance from the canvases. One sponge contains only water, while the other has had soap added. The water-soaked sponge has no effect on removing the oil, but the soaped sponge quickly dissolves a good amount of the oil.
Soap molecules contain long hydrocarbon chains, making them relatively non-polar. Oils and other substances that have a greasy feel to them are often non-polar molecules. Water will not be effective in removing oils, since water is relatively polar. The non-polar soap solution will effectively dissolve non-polar oils, making soap an effective cleaner.
Two large graduated cylinders are filled halfway with water and halfway with vegetable oil. Two layers are visible in both cylinders. Soap is added to one graduated cylinder and both cylinders are stoppered and sealed with parafilm. The cylinders are shaken and allowed to sit for about 1 minute. The cylinder that did not contain soap will separate into two layers once more, but the cylinder that contained the soap will remain as one opaque layer.
Soap molecules contain long hydrocarbon chains, making them relatively non-polar. Oils and other substances that have a greasy feel to them are often non-polar molecules. Water will not typically mix with oils unless there is an emulsifying agent present to act as a chemical "mediator" between the two substances. Since soap molecules have both polar and non-polar ends, they contain sites that can interact with both polar and non-polar molecules
Description: Na and Mg metals react with oxygen to produce basic oxides that turn universal indicator purple (basic). Carbon on the other hand reacts with oxygen to produce an acidic oxide that turns universal indicator orange (acidic).
Concept: Most metals react with oxygen to produce basic oxides. Most non-metals react with oxygen to produce acidic oxides.
Lithium, sodium, and potassium metals are sliced and then a small sample of each is reacted with water.
The alkali metals are soft and silvery. They are also the most reactive metals having the lowest ionization energies. They react readily with water, lithium being the least reactive and potassium the most.
Samples of Mg and Ca are displayed. Mg and HCl produce less bubbles than Ca and HCl. Mg and H2O produces less hydroxide and therefore less pink with phenolphthalien than Ca and H2O.
The alkaline earth metals are less reactive and harder compared to the alkali metals. They do not react as readily with water. Mg is less reactive than Ca.
Many samples of elements are available to be displayed in class.
An element is a substance that cannot be decomposed by any chemical reaction into simpler substances; a type of matter composed of only one kind of atom, each atom of a given kind having the same properties.
Small cards showing each element and their atomic number are arranged to form the periodic table.
When the elements are arranged by atomic number, their physical and chemical properties such as atomic radius, ionization energy and electron affinity, vary periodically.
He, Ne, and Ar discharge tubes show different colors.
The electrons of an element are excited in a discharge tube. As these excited electrons fall back from one energy level to another, they will emit photons of light. These photons will have different colors depending on the element and its discrete energy levels. That is, different wavelengths of light (colors) will be emitted when the electrons of different elements go down the steps between their energy levels. Each element will have its own set of steps, therefore each will have its own color or set of colors.
Samples of Cl2 gas, Br2 liquid, and I2 solid are displayed in round 1 L glass bulbs.
When excited, electrons of different halogens emit different colors.
Different salts are burned within glass Petri dishes. Sodium burns orange, potassium - purple/blue, barium - green, copper – blue/green, and lithium or strontium – red
When an element is burned, the electrons will be excited. Then as these electrons fall back from one energy level to another, they will emit photons of light. These photons will have different colors depending on the element and its discrete energy levels.
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The space filling model is compared to the ball and stick model.
The atoms of different elements have particular sizes. Space filling molecular models show the relative atomic sizes of the atoms of the molecule
Models of different atomic orbitals are displayed.
The orbits of electrons change depending on their energy level.
A vial containing an ionic compound containing a paramagnetic metal is hung from a string from a bar on a ring stand in between the gap in a gap magnetic and the vial sticks to one of the sides of the magnet. Repeat with a diamagnetic metal and the vial just sits in the middle of the gap, not sticking to either side.
Paramagnetism is the tendency of a species with unpaired electrons to be attracted by an external magnetic field. A species with all of its electrons paired exhibits diamagnetism and is slightly repelled by a magnetic field.
We have a collection of discharge tubes of various sizes. Most are small, but we have a few that are large enough that their atomic line spectra can be viewed through a hand held diffraction grading from the balcony of the large auditorium. If desired, the view of any atomic spectra through a spectroscope can be projected onto a television screen.
When the gas of an element is heated in a lamp and the resulting light is spread out with a diffraction grading, a line spectrum will be observed showing only certain colors of wavelengths related to the energy levels of the atom of the element.
Five different metal ions are passed into the burning gas in a Bunsen burner. Each metal as it is burned will emit a different color.
When an element is burned, the electrons will be excited. Then as these electrons fall back from one energy level to another, they will emit photons of light. These photons will have different colors depending on the element and its discrete energy levels.
Different salts are burned within glass Petri dishes. Sodium burns orange, potassium - purple/blue, barium - green, copper – blue/green, and lithium or strontium – red.
When an element is burned, the electrons will be excited. Then as these electrons fall back from one energy level to another, they will emit photons of light. These photons will have different colors depending on the element and its discrete energy levels.
Liquid oxygen is poured or dripped into a gap magnet and seen to stick to the poles.
Liquid oxygen’s MO has two unpaired electrons, making it paramagnetic and susceptible to a magnetic field.
Six, colored solutions are shown to the students while a color wheel and a visible light spectrum is projected onto the wall. The students are shown transparencies of six different absorbance spectra, and are asked to aid in predicting which spectrum corresponds to which solution.
If a solution appears to be red, then it is reflecting red light and absorbing the color of light that lies across from red on the color wheel.
The colors of various transition metals can be displayed on the overhead.
Ions of the transition elements exist in aqueous solution as complex ions. Transition-metal compounds are often colored. The color results from the transition of electrons between the two closely spaced d orbitals. The transitions are due to the electric field of the compound's ligands.
A number of different types of chemical reactions are demonstrated.
Observations of what happens when two chemicals are mixed together can clue us to if and how the chemicals react.
An endothermic reaction lowers temperature in flask so that the flask will freeze and stick to a wet piece of wood. An endothermic reaction is used in drug store instant cold pack. An exothermic reaction in a Styrofoam cup will significantly raise the temperature in the cup.
Some chemical reactions absorb heat from the surroundings, resulting in a cooling of the surroundings (Endothermic Reactions). Some chemical reactions evolve heat, resulting in a warming of the surroundings (Exothermic Reactions).
The Collisions Cube is set up to demonstrate chemical equilibrium. If the blower powers are equal, an even distribution of each color should be established in each chamber. Adjusting one blower to roughly half the power of the other will cause the ping-pong balls to begin accumulating on the side with less blower power. Once equilibrium is established, roughly 1/3rd of the balls should be on one side while the other 2/3rd will be on the other side. The net change in the system at this point should still be about zero if observed closely.
Equilibrium is a state in which the new change in a system is 0. Equilibrium doesn’t necessarily mean having equal amounts of reactant and product.
When the blowers of the Collisions Cube are turned on, the balls will mix and distribute themselves evenly among the two sides. The power of this demonstration lies in the question that should be asked after mixing has occurred: "How long do we need to leave the machine running before we will see the ping-pong balls separate into groups of like colors once more?" It can be noted that un-mixing the balls will take a bit of effort and will not occur without some type of outside force interfering and using up energy.
Entropy is a measure of incapability for a reaction to do further work.
A Gummi Bear is dropped into a test tube of heated potassium chlorate. The Gummi Bear is combusted.
Exothermic reactions produce a lot of heat. Potassium Chlorate is a strong oxidizing agent; a fire may start when it is mixed with combustible materials.
Sulfuric acid is added to 0° C water in one beaker and 0° C ice in another. The temperature in the beaker of water increases and the temperature in the beaker of ice decreases.
Heat is released when acid reacts with water causing the temperature of the water to increase. However if the water is frozen initially the heat from this reaction is absorbed by the phase change of the ice molecules to liquid water. Additionally, the temperature of this water will decrease due to the freezing point depression effect of the solute (the acid).
Water is added to NaCl and the temperature decreases by about 3°C; water is added to KNO<sub>3</sub> and the temperature decreases by about 12°C; water is added to LiCl and the temperature increases by about 70°C.
Heats of solution can be exothermic and endothermic.
The Collisions Cube is filled with a gross of ping-pong balls and is left without a divider. The variacs should be set to a high voltage (around 90), and the ping-pong balls should be said to represent the molecules near the surface of a liquid. The lid is then removed from the machine and students watch as the molecules "evaporate" into the room.
Molecules near the surface of a liquid will sometimes evaporate into the air around it.
Many samples of elements are available to be displayed in class.
An element is a substance that cannot be decomposed by any chemical reaction into simpler substances; a type of matter composed of only one kind of atom, each atom of a given kind having the same properties.
The colors of various transition metals can be displayed on the overhead.
Ions of the transition elements exist in aqueous solution as complex ions. Transition-metal compounds are often colored. The color results from the transition of electrons between the two closely spaced d orbitals. The transitions are due to the electric field of the compound's ligands.
Molecular models of square planar, tetrahedral, etc. and/or octahedral cis and trans isomers and optical isomers are displayed.
Compounds formed by elements are structured in different ways.
Four beakers containing a green solution of nickel (II) solution are displayed. When successively more drops of ethylenediamine are added to the beakers, the solutions display colors from light blue to violet characteristic of various nickel complexes.
Ions of the transition elements exist in aqueous solution as complex ions. Transition-metal compounds are often colored. The color results from the transition of electrons between the two closely spaced d orbitals. The transitions are due to the electric field of the compound's ligands.
An acidic chromium (VI) solution is shown to be yellow. After gargling with mouthwash containing alcohol, the demonstrator blows air through a straw into the solution. The alcohol from their breath reacts with dichromate, changing the solution from medium yellow to light green.
Transition metal compounds are often colored and a change in oxidation state of the metal often accompanies the color change. The alcohol on the demonstrator’s breath reduces Cr6+ to Cr3+, changing the solution color from yellow to green, while at the same time oxidizing the primary alcohol to a carboxylic acid. This demo can be shown to demonstrate the reduction of metals and the oxidation of organic compounds.
A flask containing a NH4VO3 solution and zinc amalgam is gently swirled and the color of the solution turns from yellow to blue. A second swirl turns the solution from blue to green. A third swirl brings the solution to a violet color.
Transition metal compounds are often colored.
Various chemicals in various amounts are added to a nickel (II) solution resulting in a variety of colors.
Ions of the transition elements exist in aqueous solution as complex ions. Transition-metal compounds are often colored. The color results from the transition of electrons between the two closely spaced d orbitals. The transitions are due to the electric field of the compound's ligands. For example, when water is the ligand the nickel complex has a green color, when ammonia is the ligand the color is blue.
Two compounds containing Fe2+ are compared in terms of color and susceptibility to a magnetic field.
Crystal field splitting in octahedral complexes arises as a result of the electron density overlap between incoming ligands and the dz2 and dx2- y2 orbitals.