a$)$ What is the $pH$ of a solution prepared by adding $25\mathrm{.}0mL$ of $0\mathrm{.}10MHN{O}_3$ to $40\mathrm{.}0m{L}^0$ of $0\mathrm{.}10MN{H}_3(aq)?30\mathrm{.}0mL$ of $0\mathrm{.}15MH{C}_2{H}_3{O}_2$ is titrated with $0\mathrm{.}10$MKOH.

a$)$ Calculate the initial $pH$ of the acetic acid solution $($before any KOH is added$).$

b$)$ Calculate the $pH$ of the resulting solution after $20\mathrm{.}0mL$ of the KOH has been added.Calculate the $pH$ at the midpoint and at the equivalence point of the titration of $25\mathrm{.}00mL$ of $0\mathrm{.}200M$ formic acid, $HCH{O}_2,$ with $0\mathrm{.}273$MNaOH.$K{a}_a(HCH{O}_2)=2\mathrm{.}1{10}^{-4}$a$)$ Calculate the $pH$ of a buffer prepared by dissolving $8\mathrm{.}00g$ of $H{C}_7{H}_5{O}_2$ and $10\mathrm{.}0$gNaC$7_7{H}_5{O}_2$ in enough water to make $500.mL$ of solution.

$Ka(H{C}_7{H}_5{O}_2)=1\mathrm{.}0{10}^{-6}$

b$)$ What will be the change in $pH$ in the solution in part $($a$)$ when $15\mathrm{.}0mL$ of $1\mathrm{.}0MHCl$ is added?

$6.$ Calculate the $pH$ at the midpoint and at the equivalence point of the titration of $25\mathrm{.}00mL$ of $0\mathrm{.}200M$ formic acid, $HCH{O}_2,$ with $0\mathrm{.}273$MNaOH.$K{a}_a(HCH{O}_2)=2\mathrm{.}1{10}^{-4}$Show by $2$ net ionic equations how $NaHC{O}_3$ may act as a buffer.