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JAMB Chemistry 1997 Question 45

Question 45

Fats, Oils and Soaps

Synthetic detergents are preferred to soap for laundry using hard water because

  1. A.detergents are water soluble while soap is not
  2. B.the calcium salts of detergents are water soluble
  3. C.the magnesium salt of soap is soluble in hard water
  4. D.soap does not have a hydrocarbon terminal chain.
Show the answer and explanation

Answer: B (the calcium salts of detergents are water soluble)

Explanation

Soap reacts with Ca2+ and Mg2+ in hard water to form insoluble scum. The calcium salts of detergents stay dissolved, so no scum forms and no detergent is wasted.