Question

Soap cannot be used for hard water why?

Answer 1

because it does not form lather in hard water so we use synthetic detergent in hard water

Answer 2

Answer:

Soaps cannot be used in hard water because they forms precipitates. When soaps are used in hard water that contains a lot of calcium and magnesium ions they cause the soap to precipitate and it is unable to form lather. This can be minimized by the addition of chemicals like sodium trimetaphosphate, borax, sodium silicate etc. These prevent the calcium and magnesium ions from reacting with the soap and allow it to form lather, thus forming precipitates.