AQA GCSE Chemistry (8462), Higher tier · Chemical analysis › Identification of ions
Practise Metal hydroxides. 14 exam-style questions plus unlimited generated ones on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
Required practical:Identifying ions (method, variables and exam tips)
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A solution forms a blue precipitate with sodium hydroxide solution. Name the metal ion in the solution.
copper(II)
Copper(II) sulfate solution reacts with sodium hydroxide solution to form a precipitate. Name the precipitate.
copper(II) hydroxide
Write the ionic equation for the formation of iron(III) hydroxide from iron(III) ions and hydroxide ions. Include state symbols.
Fe3+(aq) + 3OH−(aq) → Fe(OH)3(s)
Name the ion that forms a brown precipitate with sodium hydroxide solution.
iron(III)
Calculate the minimum amount, in moles, of sodium hydroxide needed to precipitate all the copper(II) ions.
0.0300 mol
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy4 marks
Sodium hydroxide solution can be used to identify some metal ions.
(a) What colour precipitate forms when sodium hydroxide solution is added to a solution containing iron(III) ions? Tick (✓) one box.[1]
Blue
Brown
Green
White
(b) A solution forms a blue precipitate with sodium hydroxide solution. Name the metal ion in the solution.[1]
(c) Give two metal ions that form a white precipitate with sodium hydroxide solution.[2]
Show the answer and mark scheme
(a)Answer: Brown
(b)Answer: copper(II)
copper(II) / copper / Cu2+
(c)
aluminium / Al3+
calcium / Ca2+
magnesium / Mg2+
Question 2Medium5 marks
A student has three unlabelled solutions. One contains aluminium ions, one contains calcium ions and one contains magnesium ions. When a few drops of sodium hydroxide solution are added to each solution, a white precipitate forms.
(a) Describe how the student could use sodium hydroxide solution to identify the solution containing aluminium ions. Give the result.[2]
(b) Sodium hydroxide solution cannot be used to tell apart the solutions containing calcium ions and magnesium ions. Explain why. Name another test that could identify the calcium ions and give the result.[3]
Show the answer and mark scheme
(a)
add excess sodium hydroxide solution (to each precipitate)
only the aluminium hydroxide precipitate dissolves (to give a colourless solution)
(b)
both form white precipitates that do not dissolve in excess sodium hydroxide solution
flame test
calcium ions give an orange-red flame (magnesium ions give no flame colour)
Question 3Hard6 marks
Sodium hydroxide solution reacts with solutions of some metal ions to form insoluble hydroxides.
(a) Write the ionic equation for the formation of iron(III) hydroxide from iron(III) ions and hydroxide ions. Include state symbols.[2]
(b) Magnesium chloride solution reacts with sodium hydroxide solution. MgCl2(aq) + 2NaOH(aq) → Mg(OH)2(s) + 2NaCl(aq) Explain why sodium ions and chloride ions are not included in the ionic equation for this reaction.[2]
(c) Write the ionic equation for the reaction between magnesium chloride solution and sodium hydroxide solution.[1]
(d) Aluminium ions have the formula Al3+. Give the formula of aluminium hydroxide.[1]
Show the answer and mark scheme
(a)Answer: Fe3+(aq) + 3OH−(aq) → Fe(OH)3(s)
Fe3+ + 3OH− → Fe(OH)3
(aq) (aq) → (s)
(b)
they are spectator ions / they do not take part in the reaction
they are in solution / aqueous both before and after the reaction