Edexcel IAL Chemistry 14.5 Hydrogen ion concentration from pH

Convert pH to [H+] before doing anything else, then carry the concentration into Kw or moles-and-volume working so the final units and significant figures stay sensible.

Exam points

Calculate [H+] from pH using 10^-pH and report the value in mol dm-3 units.
Use Kw = [H+][OH-] to obtain [OH-] after calculating the hydrogen ion concentration.
Find dilution volume by conserving moles of H+ before and after the pH change.

[Maximum number: 1]

This question is about sulfuric acid and its salts.

Sulfur trioxide is used to produce sulfuric acid.

The pH of a $0.10 \mathrm{~mol} \mathrm{dm}^{-3}$ solution of sulfuric acid at $25^{\circ} \mathrm{C}$ is 0.97 .

Calculate the concentration of hydrogen ions, in $\mathrm{mol} \mathrm{dm}^{-3}$ , in this solution.

calculation of $\left[\mathrm{H}^{+}(\mathrm{aq})\right] /\left[\mathrm{H}_{3} \mathrm{O}^{+}(\mathrm{aq})\right]$

Example of calculation:
$\begin{aligned} & {\left[\mathrm{H}^{+}(\mathrm{aq})\right] /\left[\mathrm{H}_{3} \mathrm{O}^{+}(\mathrm{aq})\right]=10^{-0.97}} & \quad=0.10715 / 0.1072 / 0.107 / 0.11\left(\mathrm{~mol} \mathrm{dm}^{-3}\right) \end{aligned}$

Ignore SF except 1 SF Ignore incorrect units

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14.5—Hydrogen-ion concentration in mol dm−3 from pH using [H+] = 10^(−pH) question 1