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Soap performs poorly in hard water because

  • A.it hydrolyses back to a free fatty acid
  • B.the pH becomes much too high
  • C.it dissolves far too rapidly
  • D.the hardness ions form an insoluble scum

Answer: D

The scum both wastes soap and deposits on fabric and fittings. Synthetic detergents were developed largely because their calcium salts remain soluble. The scum is both a waste and a nuisance. Softening the water restores soap performance.

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