6 exam-style questions with full mark schemes and model answers. Write your own answer and the AI examiner marks it against the mark scheme.
A technician finds an unlabelled bottle containing a white solid known to be a single soluble salt. A student is asked to identify both the positive (metal) ion and the negative ion present.
The student dissolves a sample in water and carries out a series of tests. The results are shown below.
| Test | Observation |
|---|---|
| Flame test (clean wire dipped in the solution) | Lilac flame |
| Add a few drops of dilute nitric acid, then silver nitrate solution | Pale yellow precipitate forms |
| Add sodium hydroxide solution to a fresh sample | No precipitate; no coloured change |
Describe how these results allow the student to identify the salt, and explain the reasoning behind each test. Name the salt the student should report. (6 marks)
Iron is extracted from iron(III) oxide in a blast furnace by reduction with carbon. One reaction that occurs is:
2Fe2O3+3C→4Fe+3CO2
(a) Explain why carbon can be used to extract iron from its oxide, but cannot be used to extract a more reactive metal such as aluminium. (2 marks)
(b) In this reaction, state which substance is reduced and which is oxidised, and explain your answers in terms of oxygen. (2 marks)
A student adds a piece of zinc metal to blue copper(II) sulfate solution. After a few minutes the blue colour fades and a pink-brown solid coats the zinc.
The overall reaction is:
Zn+CuSO4→ZnSO4+Cu
(a) Explain, in terms of the reactivity series, why this displacement reaction happens. (1 mark)
(b) This is a redox reaction. Write the two ionic half-equations for the zinc and for the copper, and state which species is oxidised. (2 marks)
Three test tubes each contain a different gas. A student carries out a test on each one. The results are:
| Tube | Test and result |
|---|---|
| A | A lit splint makes a squeaky pop |
| B | A glowing splint relights |
| C | The gas turns limewater milky (cloudy white) |
(a) Identify the gas in each tube, A, B and C. (3 marks)
Sodium hydroxide solution can be used to identify some metal ions in solution because they form coloured, insoluble hydroxide precipitates.
A student adds sodium hydroxide solution to two separate unknown solutions:
(a) Identify the metal ion present in solution X and in solution Y. (2 marks)
Modern analytical laboratories often use flame emission spectroscopy (an instrumental method) to identify metal ions, instead of carrying out a flame test by eye.
Give one advantage of using an instrumental method such as flame emission spectroscopy compared with a simple flame test. (1 mark)