A student plans an investigation to find the number of waters of crystallisation, xxx, in a sample of hydrated iron(II) ethanedioate, FeC2O4⋅xH2O\text{FeC}_2\text{O}_4 \cdot x\text{H}_2\text{O}FeC2O4⋅xH2O.
Both iron(II) ions and ethanedioate, C2O42−\text{C}_2\text{O}_4^{2-}C2O42−, ions are oxidised by acidified potassium manganate(VII). Construct the half-equation for the oxidation of ethanedioate ions to carbon dioxide.
The student prepares a 250.0 cm3250.0\text{ cm}^3250.0 cm3 solution of hydrated iron(II) ethanedioate by dissolving 1.618 g1.618\text{ g}1.618 g of FeC2O4⋅xH2O\text{FeC}_2\text{O}_4 \cdot x\text{H}_2\text{O}FeC2O4⋅xH2O in dilute sulfuric acid. The student titrates 25.0 cm325.0\text{ cm}^325.0 cm3 samples of this solution with 0.0200 mol dm−30.0200\text{ mol dm}^{-3}0.0200 mol dm−3 KMnO4\text{KMnO}_4KMnO4. The student's burette readings (measured to the nearest 0.05 cm30.05\text{ cm}^30.05 cm3) are given in the table below:
| Titration | 1 | 2 | 3 |
|---|---|---|---|
| Final reading / cm3\text{cm}^3cm3 | 27.80 | 28.20 | 27.90 |
| Initial reading / cm3\text{cm}^3cm3 | 0.85 | 1.15 | 0.40 |
Complete the table and calculate the mean titre of KMnO4\text{KMnO}_4KMnO4 using only the concordant results.
The uncertainty in each burette reading is ±0.05 cm3\pm 0.05\text{ cm}^3±0.05 cm3. Calculate the percentage uncertainty for the titre in Titration 1. Give your answer to 2 decimal places.
In the titration, 5 mol5\text{ mol}5 mol of iron(II) ethanedioate reacts with 3 mol3\text{ mol}3 mol of manganate(VII) ions. Analyse the student's results to find the value of xxx in FeC2O4⋅xH2O\text{FeC}_2\text{O}_4 \cdot x\text{H}_2\text{O}FeC2O4⋅xH2O. (Relative atomic masses: H=1.0\text{H} = 1.0H=1.0, C=12.0\text{C} = 12.0C=12.0, O=16.0\text{O} = 16.0O=16.0, Fe=55.8\text{Fe} = 55.8Fe=55.8)
199 exam-style questions on OCR A A Level Chemistry Atoms and reactions, covering Atomic structure and isotopes, Compounds, formulae and equations, Amount of substance, Acids, and Redox. Each one has a worked solution and a mark scheme showing where the marks go.