Purification of water with ferric chloride Ferric chloride ($\ce{FeCl3}$) is a chemical used in water treatment. If ferric chloride is added to a water sample containing calcium bicarbonate, would the $\mathrm{pH}$ of the solution decrease or increase?
If I'd state that the pH drops, would you know why?

If you dissolve $\ce{FeCl3}$ in water, a hexaqua complex is formed. These complexes are known as cation acids:

$$\ce{[Fe(H2O)6]^{3+} + H2O -&gt; [Fe(OH)(H2O)5]^{3+} + H3O+}$$