pH calculation q (1 Viewer)

[copynpaste]

What is the pH of the resulting solution when 50mL of 0.15M potassium hydroxide solution and 150mL of 0.10M sulfuric acid are mixed?

[answer is 0.95]

I know that you're meant to find the moles of KOH & H2SO4 used, and then find the no. of moles in excess (for H2SO4)... but don't really understand why you do that. Aren't the excess moles the ones that haven't reacted? (So why would you use it to find the pH of the resulting solution? )

 

[faisalabdul16]

The excess moles means that after a reaction has occurred and finished, there is still an amount of a substance left over in the reaction flask, whether it may be acidic or basic in nature. Hence why you use the excess moles to calculate the pH because that is the only thing that remains in the vessel, everything else has reacted.