OCR GCSE Chemistry A (Gateway)
OCR GCSE Chemistry A C5.1 Monitoring Chemical Reactions Exam Questions
Free OCR GCSE Chemistry A exam questions for C5.1 Monitoring Chemical Reactions, with a mark scheme for every pack. Covers concentration of solutions, titrations, molar gas volume, theoretical and percentage yield, atom economy and choosing reaction pathways.
C5.1 Monitoring Chemical Reactions exam questions
1 question pack of real past exam questions, each with its mark scheme. Do not stop after a few: answer as many as you can without notes, then mark every answer with the mark scheme. The more questions you do, the more quickly you will spot how examiners ask about each idea.
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About OCR GCSE Chemistry A C5.1 Monitoring Chemical Reactions
C5.1 covers quantitative chemistry used to monitor and judge chemical reactions. On the OCR Gateway Chemistry A course it opens Topic C5 Monitoring and controlling chemical reactions, assessed in Paper 2 (Foundation) or Paper 4 (Higher). You calculate concentrations, carry out and analyse titrations, and use yield and atom economy to compare reaction pathways; Higher students also use molar gas volume. It builds directly on moles from C3.1 and acids from C3.3, and links to industrial processes in C6.1. Examiners typically test multi-step titration calculations, the PAG titration method, percentage yield and atom economy calculations and reasons why yields are below 100%.
What you need to know
- Concentration Concentration in g/dm3 = mass of solute / volume in dm3. Higher: concentration in mol/dm3 = moles / volume in dm3. Convert cm3 to dm3 by dividing by 1000.
- Titrations A burette is used to add acid to a known volume of alkali (measured with a pipette) containing an indicator until the end point. Repeat until concordant titres (within 0.10 cm3) are obtained and calculate a mean.
- Titration calculations (Higher) Find moles of the solution of known concentration, use the mole ratio from the equation, then calculate the unknown concentration.
- Molar gas volume (Higher) One mole of any gas occupies 24 dm3 at room temperature and pressure. Volume of gas = moles x 24 dm3.
- Percentage yield Percentage yield = actual yield / theoretical yield x 100. Yields are less than 100% because of reversible reactions, side reactions and product lost during separation.
- Atom economy Atom economy = Mr of desired product / total Mr of all reactants x 100. A high atom economy means less waste, which is more sustainable and economic; the best pathway also considers yield, rate, equilibrium and usefulness of by-products.
Common mistakes in C5.1 Monitoring Chemical Reactions
- Forgetting to convert cm3 to dm3 in concentration calculations. Divide by 1000.
- Confusing percentage yield with atom economy. Yield compares actual and theoretical product mass; atom economy compares the Mr of the desired product with all reactants.
- Including anomalous titres in the mean. Only use concordant results.
- Reading the burette from the top of the meniscus. Read from the bottom of the meniscus at eye level.
- Using 24 dm3 for liquids or solids. Molar gas volume applies only to gases at room temperature and pressure.
Try three C5.1 Monitoring Chemical Reactions exam-style questions
1. 25.0 cm3 of sodium hydroxide solution was neutralised by 20.0 cm3 of 0.100 mol/dm3 hydrochloric acid. NaOH + HCl -> NaCl + H2O. Calculate the concentration of the sodium hydroxide. (3 marks)
Show the mark scheme answer
Moles HCl = 0.100 x 20.0 / 1000 = 0.00200 mol; ratio 1 : 1 so 0.00200 mol NaOH; concentration = 0.00200 / 0.0250 = 0.0800 mol/dm3.
2. Calculate the atom economy for making calcium oxide: CaCO3 -> CaO + CO2. (Mr: CaCO3 = 100, CaO = 56) (2 marks)
Show the mark scheme answer
56 / 100 x 100; = 56%.
3. Calculate the volume of carbon dioxide at room temperature and pressure produced by 0.25 mol of calcium carbonate reacting completely. (2 marks)
Show the mark scheme answer
1 mol CaCO3 gives 1 mol CO2, so 0.25 mol CO2; volume = 0.25 x 24 = 6.0 dm3.
C5.1 Monitoring Chemical Reactions FAQs
What does OCR GCSE Chemistry A C5.1 cover?
It covers concentration of solutions, titrations, molar gas volume, percentage yield, atom economy and how chemists choose between reaction pathways.
Which paper is C5.1 examined in?
Topic C5 is assessed in Paper 2 (Foundation) or Paper 4 (Higher).
Which equations do I need for C5.1?
Learn concentration = mass (or moles) / volume, percentage yield = actual / theoretical x 100, atom economy = Mr of desired product / total Mr of reactants x 100, and gas volume = moles x 24 dm3.
