Analysis of inorganic compoundsEdexcel A-Level Chemistry: Subtopic test

1. 1
   A school technician has labelled three white solids as sodium carbonate, sodium hydrogencarbonate and sodium sulfate, but the labels have come off. She has dilute hydrochloric acid, limewater and aqueous barium chloride.

   (a)

   Dilute hydrochloric acid is added to a sample of each solid. Which observation shows that a solid contains a carbonate or hydrogencarbonate?

   [1 mark]

   • AA gas is given off that turns damp red litmus paper blue
   • BA white precipitate forms immediately
   • CA colourless gas is given off that relights a glowing splint
   • DA colourless gas is given off that turns limewater milky

   (b)

   Which is the correct ionic equation, with state symbols, for sodium carbonate solution reacting with excess dilute hydrochloric acid?

   [1 mark]

   • ACO₃²⁻(aq) + H⁺(aq) → CO₂(g) + H₂O(l)
   • BCO₃²⁻(aq) + 2H⁺(aq) → CO₂(g) + H₂O(l)
   • CCO₃²⁻(aq) + 2H⁺(aq) → CO(g) + H₂O(l)
   • DNa⁺(aq) + Cl⁻(aq) → NaCl(aq)

   (c)

   Write an ionic equation, with state symbols, for the reaction of hydrogencarbonate ions with dilute acid, and state how the gas formed is identified.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   An environmental analyst tests a sample of river water for dissolved sulfate ions using acidified aqueous barium chloride.

   (a)

   The sample is acidified with dilute hydrochloric acid before barium chloride solution is added. Why is the acid added?

   [1 mark]

   • ATo increase the solubility of barium sulfate so that it dissolves
   • BTo oxidise the sulfate ions so that they react with barium ions
   • CTo remove carbonate ions, which would otherwise form a white precipitate of barium carbonate
   • DTo supply the barium ions needed for the precipitate

   (b)

   Which is the correct ionic equation, with state symbols, for the positive test for sulfate ions?

   [1 mark]

   • ABa²⁺(aq) + SO₄²⁻(aq) → BaSO₄(s)
   • BBa²⁺(aq) + SO₄²⁻(aq) → BaSO₄(aq)
   • CBa⁺(aq) + SO₄²⁻(aq) → BaSO₄(s)
   • DBa²⁺(aq) + 2SO₄²⁻(aq) → Ba(SO₄)₂(s)

   (c)

   Adding excess acidified barium chloride to 25.0 cm³ of the sample gives 0.466 g of dry barium sulfate (M = 233 g mol⁻¹). Calculate the amount of sulfate ions in the sample and their concentration in mol dm⁻³.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A farm technician is analysing a fertiliser that is believed to be ammonium sulfate, (NH₄)₂SO₄.

   (a)

   Describe how you would show that the fertiliser contains ammonium ions. Include the observation and an ionic equation with state symbols.

   [3 marks]

   (b)

   A 2.64 g sample of the fertiliser (M = 132 g mol⁻¹) is warmed with excess sodium hydroxide solution. Write the balanced equation and calculate the volume of ammonia gas produced at room temperature and pressure (molar volume 24.0 dm³ mol⁻¹).

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A technician has three unlabelled white solids: ammonium carbonate, ammonium sulfate and ammonium chloride. She has dilute hydrochloric acid, dilute nitric acid, aqueous barium chloride, aqueous silver nitrate, aqueous sodium hydroxide, limewater and damp red litmus paper.

   (a)

   Describe a sequence of tests that would allow her to identify each of the three solids, stating the observations and giving ionic equations. Include a test that confirms the cation present in all three solids.

   [6 marks]

   (b)

   Evaluate why the order of the tests, and the choice of acid used for acidification, matters when analysing a sample that may contain carbonate, sulfate and chloride ions.

   [6 marks]

   Total for question 4: 12 marks

End of questions