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Emulsification
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
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The Effectiveness of Soap vs. Water on Grease Removal
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.
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Soap Scum
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.
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The Golden Penny
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.
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Osmosis and Semi-Permeable Membranes
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.
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The Tyndall Effect
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.
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Saturated and Supersaturated Solutions
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.
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Solubility of Alcohol: Miscible and Immiscible Liquids
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.
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Heat of Solution
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.
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