Liquid black soap is made by boiling palm oil with liquid extract of ash. The function of the ash is to provide the ?

Analysis

The question asks for the chemical role of wood ash in the traditional process of making black soap (saponification).

Concept Explanation

The production of soap is a chemical process known as saponification. Saponification involves the reaction between a fat or oil (in this case, palm oil) and a strong base (an alkali).

• Palm oil contains triglycerides (esters of glycerol and fatty acids).
• Wood ash contains potassium carbonate ($K_2CO_3$). When wood ash is mixed with water and filtered, the resulting extract is alkaline. This is because the potassium carbonate reacts with water to form potassium hydroxide ($KOH$), which is a strong alkali.
• When this alkaline extract is boiled with palm oil, the alkali breaks down the fat into glycerol and the potassium salt of the fatty acid (which is the soap).

Step-by-Step Solution

1. Identify the reactants: The process uses palm oil (the fat/oil source) and ash extract.
2. Determine the chemical nature of the ash extract: Ash extract is rich in potassium carbonate ($K_2CO_3$), which creates an alkaline solution.
3. Apply the saponification principle: For soap to form, the oil must react with a base (alkali).
4. Conclusion: Since the ash extract provides the base necessary for the reaction to occur, its function is to provide the alkali.

Identification of the Answer

• A. Acid: Incorrect. Acids do not react with oils to form soap.
• B. Ester of alkanoic acid: Incorrect. This is what the palm oil itself contains; the ash does not provide this.
• C. Alkali: Correct. The ash extract provides the potassium hydroxide/carbonate needed to saponify the oil.
• D. Alkanol: Incorrect. Alkanol (glycerol) is a byproduct of the reaction, not the starting material provided by the ash.

Exam Tip

Remember the mnemonic "F.A.S.": Fat + Alkali = Soap. Whenever you see a question about soap production (saponification), always look for the option that mentions an alkali (like $NaOH$ or $KOH$) or a base!