Question

Why hard water is not suitable for washing clothes? Explain with equation

Answer 1

Hard water

• Hard water contains soluble salts of calcium (Ca) and magnesium (Mg).
• It does not give lather with soap. this is because of the precipitation of the insoluble soap
• The hardness of water is due to chloride of calcium and bicarbonate of magnesium

Disadvantages of using hard water

• The hard water cannot be used for washing clothes because it contains Ca²⁺ and Mg²⁺ ions, which react with soap (i.e, sodium stearate, C₁₇H₃₅COONa, or other sodium or potassium salt of higher fatty acids) to form scum or precipitate of Ca/Mg-stearate

$$\begin{gathered} \underset{\mathrm{sodium}\mathrm{stearate}\left(\mathrm{soap}\right)}{2{\mathrm{C}}_{17}{\mathrm{H}}_{35}{\mathrm{COO}}^{-}{\mathrm{Na}}^{+}\left(\mathrm{s}\right)}+\underset{\mathrm{From}\mathrm{hard}\mathrm{water}}{{\mathrm{M}}^{2+}}\to \underset{\mathrm{Metal}\mathrm{stearate}(\mathrm{white}\mathrm{curdy}\mathrm{ppt})}{{\left({\mathrm{C}}_{17}{\mathrm{H}}_{35}\mathrm{COO}\right)}_2\mathrm{M}\left(\mathrm{s}\right)\downarrow }+2{\mathrm{Na}}^{+} \\ \mathrm{where},\mathrm{M}=\mathrm{Ca}\mathrm{or}\mathrm{Mg} \end{gathered}$$

• However, after the precipitation of all the Ca²⁺ and Mg²⁺ ions present in the water, the water becomes soft and gives lathers with soap. Thus, lots of soap get wasted if clothes are washed with hard water. hence it is unsuitable for laundry i.e.washing clothes.