Question:
What is the result when soap is used in hard water?
What is the result when soap is used in hard water?
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Hard water contains Ca2+ and Mg2+ ions that form insoluble scum with soap.
Updated On: Oct 1, 2026
- Micelles
- Scum
- Emulsion
- Gel
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Verified By Collegedunia
The Correct Option is B
Solution and Explanation
Step 1: Understanding the Concept:
Soap is the sodium or potassium salt of a long-chain fatty acid. Hard water contains \(\text{Ca}^{2+}\) and \(\text{Mg}^{2+}\) ions.
Step 2: Write the reaction:
\[ 2\text{C}_{17}\text{H}_{35}\text{COONa} + \text{Ca}^{2+} \rightarrow (\text{C}_{17}\text{H}_{35}\text{COO})_2\text{Ca} \downarrow + 2\text{Na}^+ \]
The calcium and magnesium salts of fatty acids are insoluble and appear as a greasy white scum.
Step 3: Why the other options are wrong.
Micelles form in soft water where soap stays soluble. Emulsion and gel are not the result of soap meeting hard water.
Final Answer:
Scum forms when soap is used in hard water. \[ \boxed{\text{(B) }\text{Scum}} \]
Soap is the sodium or potassium salt of a long-chain fatty acid. Hard water contains \(\text{Ca}^{2+}\) and \(\text{Mg}^{2+}\) ions.
Step 2: Write the reaction:
\[ 2\text{C}_{17}\text{H}_{35}\text{COONa} + \text{Ca}^{2+} \rightarrow (\text{C}_{17}\text{H}_{35}\text{COO})_2\text{Ca} \downarrow + 2\text{Na}^+ \]
The calcium and magnesium salts of fatty acids are insoluble and appear as a greasy white scum.
Step 3: Why the other options are wrong.
Micelles form in soft water where soap stays soluble. Emulsion and gel are not the result of soap meeting hard water.
Final Answer:
Scum forms when soap is used in hard water. \[ \boxed{\text{(B) }\text{Scum}} \]
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