Question

If the water contains dissolved Calcium hydrogen carbonate, out of soaps and synthetic detergents which one will you use for cleaning clothes?

Answer 1

Hint If Calcium ions are present in the solution, then water is called hard water. Calcium ions react with the active ingredient of soaps and detergents and one of them forms insoluble compounds.

Complete Step-by-Step Solution:
- As Calcium hydrogen carbonate is present in the solution when we use soap or detergent, it will react with them. Let’s see the reaction to get a better idea. Suppose ${S^ - }N{a^ + }$ is soap and ${D^ - }N{a^ + }$ is detergent molecule.
$2{S^ - }N{a^ + } + Ca\left( {HC{O_3}} \right) \to {\left( {{S^ - }} \right)_2}C{a^{2 + }} + NaHC{O_3}$
$2{D^ - }N{a^ + } + Ca\left( {HC{O_3}} \right) \to {\left( {{D^ - }} \right)_2}C{a^{2 + }} + NaHC{O_3}$
- So, these products form in case of soap and detergent, But out of these two, salt of Calcium with soap is not soluble in water and it will stick with clothes while washing and cause interference. Hence it will decrease the efficiency of soap.
- While in the case of detergent, the formed salt is soluble in water and it does not have any problem with clothes as it has a sulfonate group. It will also not affect the efficiency of detergent.

Additional Information:
- Sodium or Potassium salts of fatty acids are generally soaps
e.g. Sodium Stearate
- Most of the detergents contain sulfonate functionality, hence it’s Calcium salts are soluble in water. Also, sulphonates are more polar than carboxylates and hence bind in a lesser extent than the latter.

Note:
As Calcium hydrogen carbonate can be removed by giving heat, it does not mean that it doesn’t make water hard. So, do not consider this solution as soft water. There is a difference between soaps and detergent in a way that they have different functional groups, so their reactivity may be different.