Chemistry

Problem

20.0\,\text{mL}

sample of

0.200\,\text{M}

\mathrm{H_2SO_4}

is accidentally mixed with

10.0\,\text{mL}

0.100\,\text{M}

NaOH. The resulting mixture is titrated to equivalence with

0.250\,\text{M}

NaOH. What additional volume of the

0.250\,\text{M}

NaOH must be delivered from the buret to reach the equivalence point? a) 12.0 mL b) 28.0 mL c) 32.0 mL d) 24.0 mL

Intuitive explanation

This is a limiting reagent problem wrapped in a titration. The key insight is that the acid and base in the initial mixture will react first, leaving either excess acid or excess base—then you figure out how much additional titrant is needed to neutralize what remains. Calculate moles of $\mathrm{H_2SO_4}$ and the NaOH already added, account for their reaction (remembering that $\mathrm{H_2SO_4}$ is diprotic), determine what's left over, then use the titrant's molarity to find the volume needed to finish the job.

Intuitive explanation

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