Yesterday I titrated a solution of calcium hydroxide in aqueous calcium chloride with $16.7~\mathrm{mL}$ of $\ce{HCl}$. More specifically, I took $25\ \mathrm{mL}$ of the calcium hydroxide in aq calcium chloride and mixed it with $25~\mathrm{mL}$ of deionized water and 3 drops of an appropriate indicator. I wrote the reaction equation as

$$\ce{Ca(OH)_2 + 2HCl -> CaCl_2 + 2H_2O}$$

But do I need to somehow take into account the aqueous calcium chloride in this equation? I know that it affects the molar solubility of the calcium hydroxide during titration but I'm not sure if this should also change my reaction equation.

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    $\begingroup$ Is it a reactant? Does it react with the other substances? $\endgroup$ – Archa Jun 30 '16 at 16:33
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    $\begingroup$ Hmmm...not sure. We did 2 experiments where the only difference was the original solution: exp #1 used calcium hydroxide and exp #2 used calcium hydroxide in aqueous calcium chloride. Everything else was the same. $\endgroup$ – whatwhatwhat Jun 30 '16 at 16:34
  • $\begingroup$ My guess would be no. $\endgroup$ – whatwhatwhat Jun 30 '16 at 16:36
  • $\begingroup$ @Archa am I right? $\endgroup$ – whatwhatwhat Jun 30 '16 at 17:42

From an instructor's point of view, you have accounted for the reaction that has taken place during titration. The point you are making surrounds the conditions the titration took place under (as you pointed out, solubility is altered, for instance), but not the chemistry of the reaction, in and of itself, which you are focused on.

In essence, you are doing the first titration in aqueous calcium chloride as well, because as soon as the titration begins, what is formed?

That said, I feel I may be missing something more of the other potential rxn conditions or possible expectations of your evaluator.

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