A 0.0250L solution of HCl is neutralized by 0.0780L of an unknown Mg(OH)2 solution. Also 0.050L of this Mg(OH)2 solution is neutralized by 0.0300L of a 0.20 M H3(PO3) solution. What is the concentration of the HCl solution

Explanation:

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In this case, for the first reaction we need to focus on, the neutralization of magnesium hydroxide by phosphoric acid, we can write up the following equation:

Whereas the acid and base react in a 3:2 mole ratio; thus, we can write:

Now, solving for the concentration of the magnesium hydroxide solution we get:

Now, for the reaction between hydrochloric acid and magnesium hydroxide we have:

Therefore, solving for the concentration of the hydrochloric acid solution we get:

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