Question

What is the formula for Hard Water?

Answer 1

1. Water that does not produce lather with soap solution readily is known as hard water.
2. The hardness of water is due to the presence of Bicarbonates, Chloride, and Sulphates of Calcium and Magnesium.
3. Example: Sea water, river water and Tap water
4. Hard water does not produce lather because the cations $\left({\mathrm{Ca}}^{2+}\mathrm{and}{\mathrm{Mg}}^{2+}\right)$ present in hard water react with soap to form insoluble precipitates.

$$\begin{gathered} {\mathrm{M}}^{2+}+2{\mathrm{C}}_{17}{\mathrm{H}}_{35}\mathrm{COONa}\to {\left({\mathrm{C}}_{17}{\mathrm{H}}_{35}\mathrm{COO}\right)}_2\mathrm{M}+2{\mathrm{Na}}^{+};\mathrm{Where}\mathrm{M}=\mathrm{Ca}\mathrm{or}\mathrm{Mg} \\ \mathrm{From}\mathrm{Hard}\mathrm{Sodium}\mathrm{Stearate}\mathrm{Metal}\mathrm{Stearate}\left(\mathrm{ppt}\right) \\ \mathrm{water}\left(\mathrm{Soap}\right) \end{gathered}$$.