The analysis of major cations and anions in a water sample collected from a city's water supply is given below. Ions present in minor concentrations are not given.
| Anions | \(Cl^-\) | \(SO_4^{2-}\) | \(HCO_3^-\) | \(CO_3^{2-}\) |
|---|
| Concentration (mM) | 1.5 | 0.5 | 1.0 | 0.01 |
| Cations | \(Na^+\) | \(Ca^{2+}\) | \(Mg^{2+}\) | \(K^+\) |
| Concentration (mM) | 2 | 0.5 | 0.25 | 0.02 |
\[ HCl \rightleftharpoons H^+ + Cl^- \qquad pK=-3 \]
\[ H_2SO_4 \rightleftharpoons 2H^+ + SO_4^{2-} \qquad pK=-3 \]
\[ H_2CO_3 \rightleftharpoons H^+ + HCO_3^- \qquad pK=6.3 \]
\[ HCO_3^- \rightleftharpoons H^+ + CO_3^{2-} \qquad pK=10.3 \]
\[ HOCl \rightleftharpoons H^+ + OCl^- \qquad pK=7.5 \]
\(HOCl\) (in %) present in the total free chlorine in the water is
(rounded off to the nearest integer).