Question

Calculate the volume of Mg(OH)2 at 0.20 M necessary to neutralize 300.0 mL of H3PO4 at 0.30 M in a titration lab?

Answer 1

I am going to change the reagent to `NaOH(aq)` at `0.40*mol*L^-1` concentration, because I doubt you could prepare a solution of `Mg(OH)_2` at that concentration....

Explanation:

We address the stoichiometric equation....

`2NaOH(aq) + H_3PO_4(aq)rarrNa_2HPO_4(aq) + 2H_2O(l)`

Please note that phosphoric acid acts as a diacid in these scenarios...and ask your lecturer if you doubt me....

`n_"phosphoric acid"=30.0*mLxx10^-3*L*mL^-1xx0.30*mol*L^-1=9.00xx10^-3*mol`...

And so we need TWO equivalents of sodium hydroxide....

`=(9.00xx10^-3*molxx2)/(0.40*mol*L^-1)=45.0*mL`

You will note that I answered the question I WANTED, not the question you asked. However, the question you asked is not chemically kosher....and please bring it to the attention of your TA....