Reactions of metal ions with hydroxide, ammonia and carbonateAQA A-Level Chemistry: Flashcards
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What do you see when NaOH is added to Cu²⁺(aq)?
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- What do you see when NaOH is added to Cu²⁺(aq)?
- A pale blue precipitate of Cu(OH)₂(H₂O)₄, insoluble in excess.
- What do you see when NaOH is added to Fe²⁺(aq)?
- A green precipitate of Fe(OH)₂(H₂O)₄, which darkens or turns brown at the surface in air.
- What do you see when NaOH is added to Fe³⁺(aq)?
- A brown precipitate of Fe(OH)₃(H₂O)₃, insoluble in excess.
- What do you see when NaOH is added to Al³⁺(aq)?
- A white precipitate that dissolves in excess to give a colourless solution.
- What does amphoteric mean?
- Able to react with both acids and bases.
- Write the equation for Al(OH)₃(H₂O)₃ with excess OH⁻.
- Al(OH)₃(H₂O)₃ + OH⁻ → [Al(OH)₄(H₂O)₂]⁻ + H₂O
- Write the equation for Al(OH)₃(H₂O)₃ with acid.
- Al(OH)₃(H₂O)₃ + 3H⁺ → [Al(H₂O)₆]³⁺
- What happens when excess ammonia is added to Cu²⁺(aq)?
- The pale blue precipitate dissolves to give a deep blue solution, [Cu(NH₃)₄(H₂O)₂]²⁺.
- Which type of reaction forms [Cu(NH₃)₄(H₂O)₂]²⁺?
- Ligand substitution.
- Does Al(OH)₃ dissolve in excess ammonia?
- No. Only copper(II) hydroxide dissolves in excess ammonia.
- What is seen with Na₂CO₃(aq) and Cu²⁺ or Fe²⁺?
- A precipitate of the metal carbonate (CuCO₃ blue-green, FeCO₃ green) and no gas.
- What is seen with Na₂CO₃(aq) and Al³⁺ or Fe³⁺?
- A hydroxide precipitate (white or brown) and effervescence of CO₂.
- Write the equation for Fe³⁺(aq) with carbonate.
- 2[Fe(H₂O)₆]³⁺ + 3CO₃²⁻ → 2Fe(OH)₃(H₂O)₃ + 3CO₂ + 3H₂O
- Why do 3+ ions give CO₂ with carbonate but 2+ ions do not?
- 3+ aqua ions are more acidic because of their higher charge/size ratio, so they can protonate the carbonate ion.
Exam questions on Reactions of metal ions with hydroxide, ammonia and carbonate
- A technician has four unlabelled bottles of aqueous solution. They contain copper(II) sulfate, iron(II) sulfate, iron(III) chloride and aluminium nitrate. She adds sodium hydroxide solution dropwise to a sample of each, and then in excess, and records the observations.Write equations to show that aluminium hydroxide is amphoteric.2 marks
- A student adds aqueous ammonia dropwise to copper(II) sulfate solution. A pale blue precipitate forms. When more ammonia is added the precipitate dissolves, giving a deep blue solution.Write an equation for the formation of the pale blue precipitate and state the role of ammonia in this reaction.2 marks
- A student adds sodium carbonate solution to separate samples of iron(II) sulfate solution and iron(III) sulfate solution of the same concentration.Describe the observations made with each solution.3 marks
Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).