A $200 \mathrm{~mL}$ sample of water has an initial $\mathrm{pH}=9$. In order to determine alkalinity, the sample was titrated using $0.02 \mathrm{~N} \mathrm{H}_2 \mathrm{SO}_4$ acid to an end point of $\mathrm{pH}=4.5$. In the titration, $25 \mathrm{~mL}$ of $0.02 \mathrm{~N}$ $\mathrm{H}_2 \mathrm{SO}_4$ acid was required. What is the total alkalinity of the sample in ' $\mathrm{mg} / \mathrm{L}$ as $\mathrm{NaHCO}_3$ '?
[Atomic weight (g/mol): $\mathrm{Ca}=40, \mathrm{Na}=23, \mathrm{H}=1, \mathrm{C}=12, \mathrm{~S}=32$, and $\mathrm{O}=16]$
- $2$
- $12$
- $21$
- $305$
