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MODEL PAPER - 1 [2026] — Science STD 10 — Question

CBSE BoardEnglish MediumSTD 10ScienceMODEL PAPER - 1 [2026]5 Marks
Question
What is the difference between soaps and detergents? State in brief the cleansing action of soaps in removing an oily spot from a fabric. Why are soaps not very effective when a fabric is washed in hard water? How is this problem resolved?
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Answer

i. Soaps are sodium salts of fatty acids whereas Detergents are sodium salts of sulphonic acids. Soaps do not act in hard water due to formation of scum while detergents do.
ii. In soaps carbon chain dissolves in oil and the ionic end dissolves in water to form micelle
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iii. Hard water contains $\mathrm{Ca}^{2+} / \mathrm{Mg}^{2+}$ ions that react with soap and form precipitates called scum.
iv. By using detergents in hard water this problem can be resolved.

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