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If you facilitate a weak acid base reaction. i.e. $\ce{NaOH + H2SO4}$. All of it may not react and the solutions will not neutralize. How can you determine how much actually reacted?

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    $\begingroup$ Welcome to Chemsitry.SE. There is a way to determine the extent of reaction of weak acids and weak bases using equilibrium calculations. However, your acid/base pair of choice is a strong acid $(\ce{H2SO4})$ and a strong base $(\ce{NaOH})$. Assuming you have stoichiometric equivalence between the two, this reaction will go to completion. $\endgroup$ – Ben Norris Nov 13 '13 at 12:03
  • $\begingroup$ @BenNorris that would also be true with a weak acid and a strong base. One should also consider that $\ce{H2SO4}$ is not that strong on the second ionization. $\endgroup$ – mannaia Mar 21 '14 at 14:58
  • $\begingroup$ @fp I think you are right. you should answer the question writing it is not a good praxis use comment to answer the question .. $\endgroup$ – G M Mar 22 '14 at 9:11
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The procedure is called titration. It consists in adding a pH indicator (that changes color depending on pH) to the solution and adding measured quantities of base or acid until the indicator changes color and determining how much reacted from the amount used.

An alternative is to use a pH meter instead of an indicator specially in automated analysis.

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As noted by Ben in the comment, $\ce{NaOH}$ and $\ce{H_2SO_4}$ are strong base and acid, respectively, so they will react till one is completely used up. Those react in 1:2 molar ratio, so it would be easiest to determine if you have more moles of one or another, and it will simply react, using one mole of $\ce{H_2SO_2}$ per two moles of $\ce{NaOH}$, until there is only one left. If there is one left, you will have a non-neutral solution in the end.

EDIT: Obvious, obvious mistake... Thanks for pointing it!

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