Question

What would be the $pH$ of a solution obtained by mixing $5g$ of acetic acid and $7.5g$ of sodium acetate and making the volume equal to $500\, mL$ ?
$\left(K_{a} =1.75 \times10^{-5}, PK_{a}=4.76\right)$

• A. $pH=4.70$
• B. $pH<\,4.70$
• C. pH of solution will be equal to pH of acetic add
• D. $4.76 <\, pH<\, 5.0$

Answer 1

Answer: (D)

$pH=pK_{a}+log \frac{\left[salt\right]}{\left[acid\right]}$
$=4.76+log \frac{\frac{7.5}{500}}{\frac{5}{500}}=4.7+log 1.5=4.87$
Hence correct answer is $4.76 <\, pH<\, 5.0$