Experiment 6:Fats, Oils, Soaps, and Deterpents 5. Explain why the hydrolyzed fat

Question

Experiment 6:Fats, Oils, Soaps, and Deterpents 5. Explain why the hydrolyzed fat mixture was poured into a concentrated salt solution to precipitate the soap. 6. What impurities were removed from the soap by washing it with cold water? Eve as emanol, base, Sat ase dissoved in woter Purifying t Ploduct. 7. Assuming a soap to be pure sodium stearate, give an equation a. which shows why its solutions are alkaline. b. for its reaction with Mg2 in hard water. c. for its reaction with hydrochloric acid.

Explanation / Answer

Solution

5) When the hydrolyzed fat mixture is poured into a concentrated salt solution, the polarity of solution is increased resulting the solubility of soap is decreased. Thus the soap is precipitated out.

6) The traces of ethanol, sodium hydroxide, sodium chloride, glycerin etc. are present as impurities in soap. These are water soluble and are removed from the soap by washing it with cold water.

7)

(a) Sodium stearate is an ionic salt having molecular formula C17H35COONa.

When it is dissolved in water, it fully dissociates into Na+ and C17H35COO- ions. The reaction is as follows

C17H35COONa => Na+ + C17H35COO-

The C17H35COO- ions are weak bases and partially ionize in water to give C17H35COOH and OH- ions:

C17H35COO- + H2O <=> C17H35COOH + OH-

Since OH- ions are generated, the pH will be greater than 7, and the solution is alkaline.

(b)

Sodium stearate reacts with magnesium and other ions and forms insoluble salts which are as follows

C17H35COONa + Mg2+ => (C17H35COO)2Mg + 2Na+

(c)

Sodium stearate reacts with dilute HCl acid to produce a greasy solid. The reaction is as follows
C17H35COONa + HCl => C17H35COOH+ NaCl

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