Lecture
Variant 1
Oxidation of ethanol to acetaldehyde
Into a test tube fitted with a gas outlet tube, place 0,5 g of potassium dichromate (K2Cr2O7), 2 cm3 of dilute sulfuric acid, and 2 cm3 of ethanol, and shake the mixture. The mixture is observed to heat up and change color.
Add boiling chips to the test tube, clamp it at an angle, and lower the gas outlet tube almost to the bottom of another test tube containing 2 cm3 of cold water and placed in a beaker of ice. Carefully heat the reaction mixture. Within 2–3 minutes, the volume of the mixture in the receiving test tube almost doubles; after that, stop heating and disassemble the apparatus. Determine the presence of the aldehyde by its smell and using qualitative reactions.
Variant 2
Isolation of higher fatty acids from soap.
Formation of insoluble salts of higher fatty acids
In a beaker, dissolve 1 g of soap shavings in 10 cm3 of distilled water (why distilled?). Divide the resulting solution into three parts.
To the first part, add 2 cm3 of a 10% solution of sulfuric acid. Heat the mixture almost to boiling. The molten fatty acids float up as a layer that solidifies as the solution cools.
To the second test tube, add 1 cm3 of a 5% solution of calcium chloride.
To the calcium salt precipitate, add a 10% solution of acetic acid. The precipitate dissolves, and fatty acids are released, forming an oily layer upon heating.
To the third test tube, add 1 cm3 of a 5% solution of copper sulfate.
Heat the test tube with the copper salt precipitate until it begins to boil; the salt then floats up as an emerald-green ring. If there is an excess of sodium soap in the solution, the experiment will not succeed. In this case, add a little more of the 5% copper sulfate solution and heat the mixture to boiling again.
Variant 3
Salting-out of soap
Pour 3–5 cm3 of an aqueous soap solution into a test tube, warm it, and add dry sodium chloride while stirring. As the solution becomes saturated with salt, the solubility of the soap decreases, the solution begins to turn cloudy, and finally the sodium soap floats above the clear liquid as curd-like flakes. This process is called salting-out; it is often used in laboratory practice and in industry for isolating organic substances from aqueous solutions.
Variant 4
Preparation of an ester
Into a test tube, place 2–3 cm3 of ethyl or isoamyl alcohol (3-methylbutan-1-ol), then approximately the same volume of acetic acid. Add 1 cm3 of concentrated sulfuric acid. For even boiling, add a little dry sand or porcelain chips. Close the test tube with a stopper fitted with a long tube, which serves as a reflux condenser. Heat the test tube for several minutes. After cooling, pour a few cm3 of water into the test tube. The liquid will separate into layers. The upper layer is the ester. When isoamyl alcohol is used, the ester has the smell of pears.
Comments