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6.2 Quantitative analysis

6.2 Quantitative analysis

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Question 56

A student wished to determine the mass of pure sulfamic acid (H3NSO3\text{H}_3\text{NSO}_3H3​NSO3​) in a sample of household kettle descaler containing inert, soluble impurities.

The student used the following method:

  • Step 1 Weigh the sample of impure kettle descaler.
  • Step 2 Dissolve the sample in 250 cm3 of distilled water in a beaker.
  • Step 3 Use a measuring cylinder to transfer 25.0 cm3 of this solution into a conical flask.
  • Step 4 Add 3 drops of phenolphthalein indicator to the flask.
  • Step 5 Fill a burette with standard sodium hydroxide solution of known concentration.
  • Step 6 Titrate the sulfamic acid solution, swirling continuously.
  • Step 7 Record the volume of sodium hydroxide required to reach the end-point.
  • Step 8 Use this single titration reading to calculate the percentage purity of the sulfamic acid.

Suggest three improvements the student could make to this method to obtain a more accurate value for the mass of pure sulfamic acid.

[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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