Edexcel IAL Chemistry Measurement Uncertainty

Practise Edexcel IAL Chemistry measurement uncertainty through burette, thermometer and balance readings, percentage uncertainty and ways to reduce it.

Exam points

Double reading uncertainties for temperature changes or titres before calculating percentage uncertainty.
Work backwards from percentage uncertainty to a titre, or state balance ranges from two mass readings.
Explain how increasing the measured change reduces percentage uncertainty without changing apparatus.

[Maximum number: 1]

In a redox titration, $0.0500 \mathrm{~mol} \mathrm{dm}^{-3}$ potassium manganate(VII) is titrated against $25.0 \mathrm{~cm}^{3}$ of a solution containing iron(II) ions.

\mathrm{MnO}_{4}^{-}+8 \mathrm{H}^{+}+5 \mathrm{Fe}^{2+} \rightarrow 5 \mathrm{Fe}^{3+}+\mathrm{Mn}^{2+}+4 \mathrm{H}_{2} \mathrm{O}

The mean titre of potassium manganate(VII) is $18.95 \mathrm{~cm}^{3}$ .

What is the percentage error in a single titre of $18.95 \mathrm{~cm}^{3}$ ?
[The uncertainty in a single burette reading is $\pm 0.05 \mathrm{~cm}^{3}$ ]

$\pm 0.20 \%$

$\pm 0.26 \%$

$\pm 0.40 \%$

$\pm 0.53 \%$

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B.1.3—Measurement uncertainty question 1