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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 4 – Identifying Cations and Anions in Aqueous Solutions

Aim:
To carry out simple test-tube reactions to identify cations and anions in aqueous solution and make accurate observations.

Overview:
Various qualitative tests are carried out to identify Group 2 metal ions, ammonium ions, hydroxide ions, carbonate ions, sulfate ions, and halide ions (chloride, bromide, iodide).


General Equipment:

Test 1 – Group 2 Metal Cations with Sodium Hydroxide

AQA A-Level Chemistry test for Group 2 metal cations with sodium hydroxide showing precipitate formation and behaviour in excess NaOH
  1. Add 10 drops of 0.1 mol dm−3 barium chloride to a test tube.
  2. Add 10 drops of 0.6 mol dm−3 sodium hydroxide. Mix.
  3. Continue adding NaOH dropwise until excess. Observe.
  4. Repeat with calcium, magnesium, and strontium chloride.

Test 2 – Group 2 Metal Cations with Sulfuric Acid

AQA A-Level Chemistry test for Group 2 metal cations with sulfuric acid showing sulfate precipitate trends
  1. Add 10 drops of 0.1 mol dm−3 barium chloride to a test tube.
  2. Add 10 drops of 1.0 mol dm−3 sulfuric acid. Mix and continue dropwise until excess.
  3. Repeat with calcium, magnesium, and strontium chloride.

Test 3 – Ammonium Ions

AQA A-Level Chemistry test for ammonium ions by warming with sodium hydroxide and using damp red litmus to detect ammonia gas
  1. Add 10 drops of 0.1 mol dm−3 ammonium chloride to a test tube.
  2. Add 10 drops of 0.4 mol dm−3 sodium hydroxide. Shake.
  3. Warm in a water bath.
  4. Use forceps to hold damp red litmus paper over the test tube. Observe for colour change (alkaline gas – ammonia).

Test 4 – Hydroxide Ions (pH Test)

AQA A-Level Chemistry hydroxide ion test using pH indicator or ammonia on filter paper with damp red litmus
  1. Add 1 cm3 of 0.4 mol dm−3 NaOH to a test tube with red litmus or indicator paper.
  2. Observe for colour change.

    3. Alternative test: place 5 drops of 1 mol dm−3 ammonia on filter paper in a petri dish with damp red litmus. Observe paper colour change.

Test 5 – Carbonate Ions

AQA A-Level Chemistry carbonate ion test generating carbon dioxide and turning limewater cloudy
  1. Add 2 cm3 of limewater (Ca(OH)2) to a test tube.
  2. In another test tube, mix 3 cm3 of 0.5 mol dm−3 sodium carbonate with 3 cm3 of 1.0 mol dm−3 HCl.
  3. Quickly deliver gas into limewater tube.
  4. Observe for white precipitate (CO2 turns limewater cloudy).

Test 6 – Sulfate Ions

AQA A-Level Chemistry sulfate ion test using barium chloride to form white barium sulfate precipitate
  1. Add equal volumes of 0.1 mol dm−3 MgSO4 and 0.1 mol dm−3 BaCl2.
  2. Observe for white precipitate (BaSO4).

Test 7 – Halide Ions (Chloride, Bromide, Iodide)

AQA A-Level Chemistry halide test showing white AgCl precipitate behaviour with ammonia
AQA A-Level Chemistry halide test showing cream AgBr precipitate behaviour with dilute and concentrated ammonia
AQA A-Level Chemistry halide test showing yellow AgI precipitate insoluble in ammonia
  1. Add 10 drops of 0.1 mol dm−3 potassium halide (Cl−, Br−, I−).
  2. Add 5 drops of dilute nitric acid.
  3. Add 10 drops of 0.05 mol dm−3 silver nitrate solution. Observe for coloured precipitate.
  4. Add excess 2 mol dm−3 ammonia and shake.
  5. Repeat steps using concentrated ammonia.
  6. Repeat with different halides.

Test 8 – Halide Ions in Solid Salts (Using Concentrated H2SO4)

AQA A-Level Chemistry test of solid potassium halides with concentrated sulfuric acid and identification of evolved gases

Must be done in a fume hood with gloves.

  1. Place a small spatula of solid potassium halide in a dry test tube.
  2. Add 2–5 drops of concentrated sulfuric acid.
  3. Observe and record.
  4. Test gas with moist blue litmus (acidic gas produced turns blue litmus paper red)
  5. Repeat with KBr and KI, using filter paper tests for Br2 or I2 gases.

Safety Notes

Recording Observations