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3.1 Introducing chemical reactions

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Question 24

A technician investigates the reaction between iron wool and oxygen using three different arrangements. Each arrangement contains 2.24 g of iron wool and enough oxygen for all the iron to react. The iron is heated to form iron(III) oxide, Fe2O3\mathrm{Fe_2O_3}Fe2​O3​, and each arrangement is cooled before its final mass is recorded.

  • In P, an open reaction vessel and its contents are placed on the balance.
  • In Q, a sealed reaction vessel and all its contents are placed on the balance.
  • In R, an open reaction vessel is placed inside a larger sealed box. The box, the reaction vessel and all their contents are placed on the balance.
ArrangementMass measured at start (g)Mass measured at end (g)
P62.8463.80
Q74.2174.21
R186.35186.35
a.

Balance the equation for the reaction.

...... Fe+...... O2→...... Fe2O3......\,\mathrm{Fe} + ......\,\mathrm{O_2} \rightarrow ......\,\mathrm{Fe_2O_3}......Fe+......O2​→......Fe2​O3​

[1]
b.

Calculate the mass of oxygen that reacts with the iron in arrangement P.

[1]
c.

A student says, ‘The iron in Q and R cannot have reacted because their balance readings did not increase.’

Describe and explain the balance results for P, Q and R.

Include in your answer:

  • whether the student's statement is correct
  • the mass of iron oxide formed in Q and in R.

Use the results and ideas about particles.

[6]
Markscheme

3.1 Introducing chemical reactions Questions

  1. GCSE
  2. /Chemistry
  3. /3.1 Introducing chemical reactions

134 exam-style questions on OCR GCSE Chemistry 3.1 Introducing chemical reactions, covering 3.1.1 Writing formulae and balanced chemical equations, 3.1.2 Formulae of compounds from ions, and state symbols, 3.1.3 Conservation of mass and observed changes in mass, 3.1.4 Half equations and balanced ionic equations, 3.1.5 The mole and the Avogadro constant, and 3.1.6 Stoichiometry, limiting reactants and reacting masses. Each one has a worked solution and a mark scheme showing where the marks go.

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