Question
Explain the formation of scum when hard water is treated with soap.
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Answer
- Hard water possesses calcium and magnesium ions which combine with soap molecules to form curdy white precipitate of calcium and magnesium salts, which is called scum.
- $2 \mathrm{C}_{17} \mathrm{H}_{35} \mathrm{COONa}+\mathrm{Ca}^{2+} \rightarrow\left(\mathrm{C}_{17} \mathrm{H}_{35} \mathrm{COO}\right)_2 \mathrm{Ca}+2 \mathrm{Na}^{+}$
- Sodium stearate (Soap) Calcium ion Calcium stearate Sodium ion
- $2 \mathrm{C}_{17} \mathrm{H}_{35} \mathrm{COONa}+\mathrm{Mg}^{2+} \rightarrow\left(\mathrm{C}_{17} \mathrm{H}_{35} \mathrm{COO}\right)_2 \mathrm{Mg}+2 \mathrm{Na}^{+}$
- Sodium stearate (Soap) Magnesium ion Magnesium stearate Sodium ion
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