When soap is added to water containing calcium or magnesium salts, the calcium ions Ca 2 + or magnesium ions Mg 2 + get interchanged with sodium ions Na + or potassium ions K + to form corresponding Ca 2 + or Mg 2 + salts which forms white precipitate called scum.

What is denatured alcohol?

To prevent the misuse of industrial alcohol for drinking purpose, the ethanol meant for industrial purpose is denatured by adding small amounts of poisonous substance like copper sulphate or methanol or pyridine. This addition makes this ethanol unfit for drinking. This alcohol is called as denatured alcohol.

Isomers are the organic compounds having same molecular formula, but different arrangements of carbon atoms or simply different structures. For example, butane can exist in two isomeric forms such as n-butane and iso-butane.