Calculate the number of moles of \(\mathrm{HCl}(\mathrm{g})\) that must be added to \(1.0 \mathrm{~L}\) of \(1.0 \mathrm{M} \mathrm{NaC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\) to produce a solution buffered at each \(\mathrm{pH}\).

a. \(\mathrm{pH}=\mathrm{p} K_{\mathrm{a}}\)

b. \(\mathrm{pH}=4.20\)

c. \(\mathrm{pH}=5.00\)