Multiple choice

Sodium carbonate does not make water hard because

  1. it is insoluble in water

  2. sodium salts of higher fatty acids are water soluble

  3. sodium salts of higher fatty acids are colourless

  4. it is a crystalline solid
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Sodium carbonate (washing soda) does not cause hardness because sodium salts of higher fatty acids are water-soluble, unlike calcium and magnesium salts which form insoluble precipitates (soap scum). The other options are incorrect: sodium carbonate is soluble in water, color is unrelated to water hardness, and being crystalline has no connection to water softening.

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