Question

(a) Give the $p^H$ value of pure water. Does it change if common salt is added to it?

(b) Classify the following solutions as acids, bases or salts.

Ammonium hydroxide, barium chloride, sodium chloride, sodium hydroxide, $H_{2}S{O}_4$ and $HN{O}_3$.

Answer 1

(a)The pH of pure water is 7. Dissolving table salt in water of any purity will not change its pH. Table salt is, well, a salt of a strong acid, $HCl$\), and a strong base, $NaOH$, so the result is that they cancel out any pH change. The only change is that now you have salty water. $NaCl$ (i.e common salt) is a salt of a strong acid and strong base. As strong acids give weak conjugate bases and strong bases give weak conjugate acids. Hence, the $C{l}^{-}$ ions are too weak to accept protons from water and $N{a}^{+}$ ions are too weak to react with $O{H}^{-}$, So there is no change in the concentration of $H^{+}$ or $O{H}^{-}$ ion concentration, so no change in pH.

(b)

Acids - $H_{2}S{O}_4$ and $HN{O}_3$.
Base - Ammonium hydroxide,Sodium hydroxide
Salt - Barium chloride, Sodium chloride,