Why must NaOH be in excess if we wish to measure the effect acid strength has on the enthalpy of neutralisation?

A few different acids are given i.e $\ce{HCl}$ , ethanoic acid, $\ce{H2SO4}$, ethanedioic acid. We want to conduct an experiment in which we measure the temperature rise for neutralisation as a measure of the enthalpy of neutralisation for each acid (no calculations are involved other than simply noting the temperature change) while using $\pu{30 cm^3}$ of $\pu{2 mol/dm^3}$ $\ce{NaOH}$. The question states that $\ce{NaOH}$ should always be in excess, but why is this so? Why can the acid not be in excess provided that we keep the total volume constant?




I think this is just to get the best possible results for your analysis. I mean, it would be better to have excess NaOH so you get a good reference because you know exactly when no more neutralization is occuring when all the acid gets used up. Better than having excess acid, though the idea is the same, but the excess is an uncertainty. Let's just say its more of a matter of being a technique that makes sense.


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