A batch of potassium hydroxide solution is labelled as having a concentration of 5.80 g dm−35.80\,\mathrm{g\,dm^{-3}}5.80gdm−3.
During quality control, a 25.0 cm325.0\,\mathrm{cm^{3}}25.0cm3 sample of the solution is transferred to a conical flask. Nitric acid of concentration 0.120 mol dm−30.120\,\mathrm{mol\,dm^{-3}}0.120moldm−3 is delivered from a burette until the end point is reached.
HNO3(aq)+KOH(aq)→KNO3(aq)+H2O(l)\mathrm{HNO_{3}(aq) + KOH(aq) \rightarrow KNO_{3}(aq) + H_{2}O(l)}HNO3(aq)+KOH(aq)→KNO3(aq)+H2O(l)
| Test | Initial burette reading / cm3\mathrm{cm^{3}}cm3 | Final burette reading / cm3\mathrm{cm^{3}}cm3 |
|---|---|---|
| A | 0.20 | 21.05 |
| B | 0.75 | 21.65 |
| C | 1.10 | 22.50 |
| D | 0.40 | 21.25 |
Only results that agree to within 0.10 cm30.10\,\mathrm{cm^{3}}0.10cm3 should be used to calculate the mean.
The Mr M_r\,Mr of potassium hydroxide is 56.
The batch is accepted if the measured mass concentration is within 0.10 g dm−30.10\,\mathrm{g\,dm^{-3}}0.10gdm−3 of the concentration stated on the label.
State which test result should be excluded when calculating the mean. Give a reason for your answer.
Calculate the mass concentration, in g dm−3\mathrm{g\,dm^{-3}}gdm−3, of potassium hydroxide in the batch.
Explain whether the batch should be accepted.
151 exam-style questions on Edexcel GCSE Chemistry 6.2 Quantitative analysis, covering 6.2.1 Concentration in mol dm⁻³ and titration calculations, 6.2.2 Percentage yield and why actual yield falls short, 6.2.3 Atom economy of a reaction, 6.2.4 Choosing a reaction pathway, and 6.2.5 Molar volume of gases and Avogadro's law. Each one has a worked solution and a mark scheme showing where the marks go.