In a mixture of a weak acid and its salt,the ratio of concentration of acid to salt is increased ten-fold. The $pH$ of the solution

What volume (in $mL$) of $0.10 \, M$ sodium formate is required to be added to $50 \, mL$ of $0.05 \, M$ formic acid to prepare a buffer solution with $pH = 4.0$? (Given: $pK_a$ of formic acid $= 3.7$)

Addition of sodium hydroxide solution to a weak acid $(HA)$ results in a buffer of $pH \ 6$. If ionisation constant of $HA$ is $10^{-5}$,the ratio of salt to acid concentration in the buffer solution will be

$2 \ g$ acetic acid and $3 \ g$ sodium acetate are present in $100 \ mL$ aqueous solution. What will be the $pH$ of the solution if the ionisation constant of acetic acid is $1.8 \times 10^{-5}$?

$1 \times 10^{-3} \ \text{mole}$ of $HCl$ is added to a buffer solution made up of $0.01 \ \text{M}$ acetic acid and $0.01 \ \text{M}$ sodium acetate. The final $pH$ of the buffer will be (given,$pK_{a}$ of acetic acid is $4.75$ at $25^{\circ} \text{C}$)

Which of the following mixtures will produce a buffer solution with $pH = 9$?