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6.2 Quantitative analysis

6.2 Quantitative analysis

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Question 26

A sample of solid sodium carbonate contained soluble, unreactive impurities.

A student tried to find the mass of pure sodium carbonate in the sample, using the following method.

  • step 1 Measure the mass of the sample of impure sodium carbonate.
  • step 2 Dissolve the sample in 100 cm3 of distilled water in a beaker.
  • step 3 Use a measuring cylinder to transfer 25.0 cm3 of this sodium carbonate solution into a conical flask.
  • step 4 Add 3 drops of methyl orange indicator to the flask.
  • step 5 Place the conical flask on a white tile.
  • step 6 Add dilute hydrochloric acid of known concentration from a burette, swirling continuously.
  • step 7 Stop when the indicator changes colour.
  • step 8 Record the volume of hydrochloric acid added.
  • step 9 Use this single titration measurement to calculate the mass of pure sodium carbonate in the sample.

Suggest three improvements to this method to obtain a more accurate mass of pure sodium carbonate.

[3]
Markscheme

6.2 Quantitative analysis Questions

  1. GCSE
  2. /Chemistry
  3. /6.2 Quantitative analysis

157 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.

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