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?
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1 Answer
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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:
$$\ce{[Fe(H2O)6]^{3+} + H2O -> [Fe(OH)(H2O)5]^{3+} + H3O+}$$
answered May 19, 2015 at 11:25
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$\begingroup$ But where does the Cl3 went in the case? $\endgroup$ Commented Apr 2, 2018 at 19:04
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$\begingroup$ @LoïcFaure-Lacroix There's no $\ce{Cl3}$ but three chloride ions $\ce{Cl-}$ acting as counter ions to the aquo complex. They just float around, happily solvated by water molecules. $\endgroup$ Commented Apr 3, 2018 at 4:41