Answer to Question #178258 in Inorganic Chemistry for David

Question

What is the % pH change if a student added 0.0025 mol of Ca(OH)₂ to a 1.00 L buffer solution containing 0.100 M HC₂H₃O₂ and 0.200 M NaC₂H₃O₂.

Answer 1

pH = pK_a - lg$\frac{C(acid)}{C(salt)}$

pKa(HC₂H₃O₂ ) = 4.75

pH₁ = 4.75 - $lg\frac{0.1}{0.2}$ = 5.05

C₂(acid) = 0.1 - 0.0025 $\times$ 2 = 0.095 M

C₂(salt) = 0.2 + 0.0025 $\times$ 2 = 0.205 M

pH₂ = 4.75 - lg$\frac{0.095}{0.205}$ = 5.86

$\Delta$pH = 5.86 - 5.05 = 0.81

%pH_change = $\frac{0.81 \times 100}{5.05}$ = 16 %

Answer: 16 %.