Soaps do not work in hard water containing calcium and magnesium ions because

Options

A. `Ca^(2+) and Mg^(2+)` ions form insoluble calcium and magnesium salts in the form of scum
B. `Na^(+) and K^(+)` present in soap react with `Ca^(2+) and Mg^(+)` and hinder cleansing process
C. a large amount of soap is to be used in presence of `Ca^(+) and Mg^(+)`
D. scum formed by combination of `Na^(+), Ca^(2+) and Mg^(2+)` stick to the cloth and are not removed on agitation

Answer

To solve the question of why soaps do not work in hard water containing calcium and magnesium ions, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Hard Water**:
- Hard water contains high concentrations of calcium (Ca²⁺) and magnesium (Mg²⁺) ions. These ions are responsible for the hardness of water.

2. **Composition of Soap**:
- Soap is typically a sodium or potassium salt of fatty acids. For example, sodium stearate (C₁₇H₃₅COONa) is a common soap.

3. **Reaction with Hard Water**:
- When soap is added to hard water, the calcium and magnesium ions react with the soap. The reaction can be represented as follows:
\[ \text{C}_{17}\text{H}_{35}\text{COONa} + \text{CaCl}_2 \rightarrow \text{Ca(C}_{17}\text{H}_{35}\text{COO})_2 + \text{NaCl} \]
- In this reaction, calcium stearate (Ca(C₁₇H₃₅COO)₂) is formed, which is insoluble in water.

4. **Formation of Scum**:
- The insoluble calcium stearate precipitates out of the solution, forming a solid residue known as scum. This scum does not dissolve in water and thus cannot effectively clean.

5. **Conclusion**:
- Since the soap forms insoluble salts with calcium and magnesium, it cannot perform its cleaning function, making it ineffective in hard water.

### Final Answer:
Soaps do not work in hard water containing calcium and magnesium ions because they form insoluble salts (scum) with these ions, rendering the soap ineffective as a cleaning agent.

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