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Atoms and reactions

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Question 73

Sodium oxalate, Na2C2O4\text{Na}_2\text{C}_2\text{O}_4Na2​C2​O4​, is the active ingredient in some brands of commercial rust-remover tablets.

An analyst carries out an experiment to determine the mass of sodium oxalate in one rust-remover tablet, using the method below.

  • Stage 1: The analyst crushes four tablets and dissolves the powdered tablets in excess dilute sulfuric acid.
  • Stage 2: The analyst makes up the solution from Stage 1 to 500.0 cm3 in a volumetric flask.
  • Stage 3: The analyst then titrates 25.0 cm3 portions of the solution obtained in Stage 2 with 0.00500 mol dm-3 potassium manganate(VII) at 60∘C60^\circ\text{C}60∘C.

The analyst obtains a mean titre of 18.20 cm3.

In this titration, 2 mol of manganate(VII) ions, MnO4−\text{MnO}_4^-MnO4−​, reacts with 5 mol of oxalate ions, C2O42−\text{C}_2\text{O}_4^{2-}C2​O42−​.

Determine the mass, in mg, of sodium oxalate in one tablet. Give your answer to 3 significant figures.

(Relative atomic masses, ArA_rAr​: C=12.0\text{C} = 12.0C=12.0, O=16.0\text{O} = 16.0O=16.0, Na=23.0\text{Na} = 23.0Na=23.0)

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Markscheme

Atoms and reactions Questions

  1. A Level
  2. /Chemistry
  3. /Atoms and reactions

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.

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