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*Revision Materials and Past Papers* 1 Atomic Structure 2 Amounts of Substance 3 Bonding 4 Energetics 5 Kinetics 6 Chemical Equilibria & Kc 7 Redox Equations 8 Thermodynamics 9 Rate Equations 10 Kp (Equilibrium Constant) 11 Electrode Potentials & Cells 12 Acids and Bases 13 Periodicity 14 Group 2: Alkaline Earth Metals 15 Group 7: The Halogens 16 Period 3 Elements & Oxides 17 Transition Metals 18 Reactions of Ions in Aqueous Solution 19 Intro to Organic Chemistry 20 Alkanes 21 Halogenoalkanes 22 Alkenes 23 Alcohols 24 Organic Analysis 25 Optical Isomerism 26 Aldehydes & Ketones 27 Carboxylic Acids & Derivatives 28 Aromatic Chemistry 29 Amines 30 Polymers 31 Amino Acids, Proteins & DNA 32 Organic Synthesis 33 NMR Spectroscopy 34 Chromatography RP1–RP12 Required Practicals

7.2 Required Practicals

1 Make up a volumetric solution and carry out a simple acid–base titration 2 Measurement of an enthalpy change 3 Investigation of how the rate of a reaction changes with temperature 4 Carry out simple test-tube reactions to identify cations anions 5 Distillation of a product from a reaction 6 Tests for alcohol, aldehyde, alkene and carboxylic acid 7 Measuring the rate of reaction, by an initial rate method, by a continuous monitoring method 8 Measuring the EMF of an electrochemical cell 9 Investigate how pH changes when a weak acid reacts with a strong base and when a strong acid reacts with a weak base 10 Preparation of, a pure organic solid and test of its purity, a pure organic liquid 11 Carry out simple test-tube reactions to identify transition metal ions in aqueous solution 12 Separation of species by thin-layer chromatography

Disclaimer:
The exact reagents, reactions, processes and equipment used in practical activities may vary between schools, colleges, and exam board exemplar methods. The essential techniques, skills, and learning objectives remain the same. Always follow the instructions, risk assessments, and safety guidance provided by your teacher or centre.


PRACTICAL 7 – Measuring the Rate of a Reaction

Aim:
To investigate how the rate of reaction between hydrogen peroxide and iodide ions depends on iodide concentration.

Overview:
Measure the time taken for a sudden blue-black colour to appear in an iodine clock mixture while changing iodide concentration to see how it affects the initial rate.


Part A – Iodine Clock Experiment (Initial Rate Method)

Key Reactions

H2O2 + 2H+ + 2I− → I2 + 2H2O

2S2O32− + I2 → 2I− + S4O62−

When all thiosulfate has reacted, iodine remains and forms a blue-black complex with starch. Time taken for this colour change indicates reaction rate.

Apparatus and Reagents

Method Summary

AQA A-Level Chemistry iodine clock setup: beaker with acid, iodide, thiosulfate, starch; peroxide added to start timing until blue-black starch–iodine complex forms.
  1. Prepare a 250 cm3 beaker with sulfuric acid, water, starch, iodide and thiosulfate (for volumes, see table below).
  2. Use a separate beaker for 10 cm3 hydrogen peroxide.
  3. Mix peroxide into main beaker and start timer.
  4. Stop timing when blue-black colour appears.
  5. Repeat with varying iodide concentrations as per table (page 3).

Table of Volumes

Exp H2SO4 (cm3) Starch (cm3) Water (cm3) KI (cm3) Thiosulfate (cm3) H2O2 (cm3)
1 25 1 20 5 5 10
2 25 1 15 10 5 10
3 25 1 10 15 5 10
4 25 1 5 20 5 10
5 25 1 0 25 5 10

Analysis

Part B – Magnesium + Hydrochloric Acid (Continuous Monitoring)

Aim:
To measure rate of hydrogen gas production when magnesium reacts with HCl at different concentrations.

Overview:
Collect hydrogen in a gas syringe (or over water) as magnesium reacts with hydrochloric acid at two concentrations, then compare the initial gradients of volume–time graphs.

Reaction

Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g)

Apparatus and Reagents

Method Summary

AQA A-Level Chemistry gas collection setup for magnesium reacting with hydrochloric acid connected to a gas syringe.
  1. Add 50 cm3 of 0.8 mol dm−3 HCl to a conical flask.
  2. Add 6 cm Mg ribbon, insert bung.
  3. Record volume of H2 gas every 15 s for 2.5 min.
  4. Repeat using 0.4 mol dm−3 HCl (prepared by diluting with water).

Analysis

  1. Plot volume of H2 (y-axis) vs time (x-axis).
  2. Draw lines of best fit and tangents at t = 0.
  3. Calculate gradients = rate.
  4. Compare rates for both acid concentrations.

Safety Notes