Ionic equations and tests for ions and gasesIB MYP Chemistry: Subtopic test

1. 1
   A technician at a water-treatment laboratory in Nairobi mixes a colourless solution of silver nitrate with a colourless solution of sodium chloride. A white solid forms at once, and the mixture is then filtered. The technician writes the reaction first as a full equation and then as an ionic equation.

   (a)

   Which pair of ions are the spectator ions in this reaction?

   [1 mark]

   • AAg⁺ and Cl⁻
   • BNa⁺ and NO₃⁻
   • CAg⁺ and NO₃⁻
   • DNa⁺ and Cl⁻

   (b)

   Which is the correct ionic equation, with state symbols, for the reaction?

   [1 mark]

   • AAg⁺(aq) + Cl⁻(aq) → AgCl(aq)
   • BNa⁺(aq) + NO₃⁻(aq) → NaNO₃(s)
   • CAg⁺(aq) + Cl⁻(aq) → AgCl(s)
   • DAgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq)

   (c)

   Explain why a white solid forms when the two solutions are mixed.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student in a school laboratory in Manchester is given three bottles of colourless solutions labelled sodium carbonate, sodium sulfate and ammonium chloride. A technician has mixed up the labels, so the student must identify each solution using chemical tests.

   (a)

   Which test shows that a solution contains sulfate ions?

   [1 mark]

   • AAdd dilute hydrochloric acid, then barium chloride solution; a white precipitate forms
   • BAdd dilute nitric acid, then silver nitrate solution; a white precipitate forms
   • CAdd dilute hydrochloric acid; bubbles form and the gas turns limewater milky
   • DAdd sodium hydroxide solution and warm; a gas turns damp red litmus paper blue

   (b)

   The student warms ammonium chloride solution with sodium hydroxide solution. Which gas is given off, and how is it identified?

   [1 mark]

   • AHydrogen, which burns with a squeaky pop
   • BCarbon dioxide, which turns limewater milky
   • CChlorine, which bleaches damp litmus paper
   • DAmmonia, which turns damp red litmus paper blue

   (c)

   Describe how the student could use dilute hydrochloric acid to show which bottle contains sodium carbonate.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A metal-plating factory in Pune releases waste water into a drain. An environmental science club collects three samples, X, Y and Z, and adds a few drops of sodium hydroxide solution to each. Sample X forms a blue precipitate, sample Y forms a green precipitate and sample Z forms a red-brown precipitate. Each sample contains only one type of metal ion.

   (a)

   Identify the metal ion present in each of samples X, Y and Z.

   [3 marks]

   (b)

   Sample X is copper(II) sulfate solution. Write the ionic equation, with state symbols, for the reaction that forms the blue precipitate, and name the two spectator ions.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   The water authority of a small town in Chile is investigating complaints about the taste of its drinking water. Inspectors suspect that run-off from fertiliser stores has added chloride ions and sulfate ions to the supply. The authority has a small field laboratory with dilute acids, silver nitrate solution and barium chloride solution, and it can also send samples to a specialist laboratory in the capital.

   (a)

   Describe a safe method the field laboratory could use to find out whether a water sample contains chloride ions, sulfate ions or both. Say how each positive result would be recognised.

   [6 marks]

   (b)

   The authority must decide whether to rely on simple chemical tests or send every sample to the specialist laboratory. Discuss the benefits and drawbacks of the simple tests and evaluate which approach the authority should choose.

   [6 marks]

   Total for question 4: 12 marks

End of questions