By adding a strong acid to the buffer solution,the $pH$ of the buffer solution

Find the concentration of sodium acetate when added to $0.1 \ M$ solution of acetic acid to form a buffer solution of $pH = 5.5$ (in $M$)? $(pK_{a} \text{ of } CH_{3}COOH = 4.5)$

$A$ buffer that is a mixture of acetic acid $(K_a = 2 \times 10^{-5})$ and potassium acetate has $pH = 5.18$. The $\frac{[CH_3COO^{-}]}{[CH_3COOH]}$ ratio in this buffer is approximately:

What is $[H^{+}]$ of a solution that is $0.01 \ M$ in $HCN$ and $0.02 \ M$ in $NaCN$ ($K_a$ for $HCN = 6.2 \times 10^{-10}$)?

Which of the following mixtures in water acts as a buffer?

The $pK_a$ of an equimolar mixture of sodium acetate and acetic acid is $4.74$. What is the $pH$ of the solution?