Soaps on reaction with hard water forms insoluble scum due to the formation of

Options

A. NaCl
B. `CaCl_(2)`
C. `C_(17)H_(35)COONa`
D. `(C_(17)H_(35)COO)^(2)Ca`

Answer

To solve the question regarding the formation of insoluble scum when soaps react with hard water, we can break it down into the following steps:

### Step-by-Step Solution:

1. **Understanding Soaps**:
- Soaps are typically sodium or potassium salts of long-chain fatty acids. They are effective in cleaning because they can emulsify oils and fats.

2. **Identifying Hard Water**:
- Hard water contains high concentrations of divalent metal ions, primarily calcium (Ca²⁺) and magnesium (Mg²⁺) ions.

3. **Reaction of Soap with Hard Water**:
- When soap is added to hard water, the calcium and magnesium ions present in the water react with the soap. The sodium (Na⁺) or potassium (K⁺) ions in the soap are displaced by the calcium and magnesium ions.

4. **Formation of Scum**:
- The reaction leads to the formation of insoluble salts, which are commonly referred to as scum. The chemical reaction can be represented as follows:
\[ \text{Soap (sodium salt of fatty acid)} + \text{Ca}^{2+} \rightarrow \text{Insoluble scum (calcium salt of fatty acid)} \]
- For example, if we take sodium stearate (C₁₇H₃₅COONa) as the soap, the reaction with calcium ions can be written as:
\[ \text{C}_{17}\text{H}_{35}\text{COONa} + \text{Ca}^{2+} \rightarrow \text{C}_{17}\text{H}_{35}\text{COO}_2\text{Ca} + \text{Na}^+ \]
- Here, C₁₇H₃₅COO⁻ (the fatty acid part) combines with Ca²⁺ to form the insoluble compound C₁₇H₃₅COO₂Ca.

5. **Conclusion**:
- The insoluble scum formed is primarily due to the formation of calcium stearate (or similar compounds depending on the fatty acid), which is represented as C₁₇H₃₅COO₂Ca.

### Final Answer:
Soaps on reaction with hard water form insoluble scum due to the formation of calcium salts of fatty acids, such as C₁₇H₃₅COO₂Ca.

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