Edexcel IAL Chemistry 14.19 Buffer pH from data

Work in moles when solutions are mixed, identify acid and conjugate base amounts after reaction and then apply Ka or Henderson-Hasselbalch consistently.

Exam points

Calculate buffer pH from Ka or pKa using the acid-to-conjugate-base ratio.
Find moles after partial neutralisation before substituting into the buffer expression.
Rearrange Ka to determine biological or inorganic buffer ion ratios from a pH value.

[Maximum number: 5]

This question is about sulfuric acid and its salts.

A buffer solution is made from $\mathrm{HSO}_{4}^{-}$ and $\mathrm{SO}_{4}^{2-}$ ions.

A buffer solution is formed by mixing
$25.0 \mathrm{~cm}^{3}$ of a solution that is $0.150 \mathrm{~mol} \mathrm{dm}^{-3}$ with respect to $\mathrm{SO}_{4}^{2-}$ ions with $75.0 \mathrm{~cm}^{3}$ of a solution that is $0.100 \mathrm{~mol} \mathrm{dm}^{-3}$ with respect to $\mathrm{HSO}_{4}^{-}$ ions.

Calculate the pH of this buffer solution.
$\left[K_{\mathrm{a}}\right.$ for $\mathrm{HSO}_{4}^{-}$ ions $=0.012 \mathrm{~mol} \mathrm{dm}^{-3}$ ]

Figure for Question 14.19—The pH of a buffer solution given appropriate data question 1 — Edexcel A-Level Chemistry A2

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14.19—The pH of a buffer solution given appropriate data question 1