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3.2.6Stoichiometry

Practical- Effect of Catalysts on Rate of Reaction — Cambridge IGCSE Chemistry 0620 Revision Notes & Topical Questions

5 min read 5 parts Lesson 20 of 28 Unit quiz

📚 Cambridge IGCSE Chemistry 0620 Hub / Topical Revision
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Curriculum Equation Key قوانين المول والحسابات الكيميائية - Moles & Stoichiometry FormulasFast Exam Solution
n = m / M_r | N = n × N_A (6.022 × 10²³) | M = n / V | V_gas = n × 22.4 L (STP)
Word Equation & Conditions: عدد المولات = الكتلة بالجرام ÷ الكتلة المولية | عدد الجسيمات = عدد المولات × عدد أفوجادرو
Location & Specifications: كيمياء التحصيلي وثانوي وبكالوريا و Cambridge IGCSE Chemistry.
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Part 1 of 5Aim and Set-Up

Aim
  • Aim To compare how different solid catalysts affect the rate of decomposition of hydrogen peroxide solution.
Equation
  • Equation 2H₂O₂(aq) → 2H₂O(l) + O₂(g), with the oxygen gas collected over water.
Catalyst choices
  • Catalyst choices Manganese(IV) oxide, MnO₂, is a common catalyst,
    • and other solid oxides such as iron(III) oxide or copper(II) oxide can also be compared.
Control variables
  • Control variables Volume and concentration of hydrogen peroxide, mass of catalyst and temperature must be the same in each test.
Safety
  • Safety Hydrogen peroxide solution is an oxidising agent that can irritate skin and eyes, so eye protection must be worn.

Part 2 of 5Method

1
Add a fixed volume of hydrogen peroxide solution to a conical flask and connect it to a measuring cylinder inverted over water.
2
Add a fixed mass of the chosen solid catalyst to the flask and close the bung quickly so that the timing starts with the reaction.
3
Record the volume of oxygen collected at regular intervals or after a fixed time.
4
Use a clean, dry flask for each catalyst so that the results are not contaminated.
5
Run a repeat test without any catalyst, then compare the volumes or the gradients of the volume–time graphs.

Part 3 of 5Interpreting Results

Interpreting Results
Gradient
  • Gradient A steeper gradient on a volume–time graph shows a faster rate of oxygen production.
Control test
  • Control test A repeat without catalyst shows whether the catalyst, and not something else, caused the faster rate.
Not used up
  • Not used up Filter and dry the catalyst afterwards;
    • its mass remains the same, showing that it was not consumed.
Explanation
  • Explanation Catalysts give an alternative pathway with lower activation energy, so more collisions are successful.
VariableTypeHow it is controlled
CatalystIndependentChange the solid used
Volume of oxygen in a fixed timeDependentMeasure with the gas collection apparatus
Hydrogen peroxide volume and concentrationControlKeep the same in each test
TemperatureControlKeep the same throughout

Part 4 of 5Worked Example

Question

  • In one test 40 cm³ of oxygen is collected in 20 s with a catalyst, and 10 cm³ in 20 s without one.
  • Calculate the rate of each reaction and state how many times faster the catalysed reaction is.

  1. Rate with catalyst = 40 cm³ ÷ 20 s = 2.0 cm³/s
  2. Rate without catalyst = 10 cm³ ÷ 20 s = 0.50 cm³/s
  3. Ratio = 2.0 ÷ 0.50 = 4

Answer 2.0 cm³/s with the catalyst and 0.50 cm³/s without, so the catalysed reaction is 4 times faster.

Part 5 of 5Exam Checklist & Tips

3.2.6 – Key Points for the Exam

  • Catalyst A substance that increases the rate of a reaction and is not used up by it.
  • Decomposition A reaction in which a single compound breaks down into two or more simpler substances.
  • Control variable A factor kept the same in every test so that the comparison is fair.
  • Oxidising agent A substance that gains electrons or oxygen, or causes another substance to lose electrons.
  • Gradient of a volume–time graph The steepness of the line, which gives the rate of gas production.

Common Mistakes

  • Changing the volume or concentration of hydrogen peroxide between tests, so the results cannot be compared fairly.
  • Leaving out the repeat test without catalyst, so the catalyst cannot be shown to be the cause of the change.
  • Stating that the catalyst produces the oxygen; the oxygen comes from the hydrogen peroxide.
  • Comparing total volumes collected at different times rather than volumes collected in the same fixed time.

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