How does a soap behave in the presence of `Ca^(2+) and Mg^(2+)` ions in solution ?

Explanation

Soap is sodium or potassium salt of fatty acid which contains a large chain of carbon atoms. Soap interacts with the `Ca^(2+) and Mg^(2+)` ions of produce insoluble salts of calcium or magnesium which separat from the solution as scum :
` underset("soap")2Na(Ft) + Ca^(2+) to underset("scum") Ca(Ft)_(2) darr + 2Na^(+)`