QUESTION 27 (7 marks)
Four unknown metals Q, X, Z and A were placed into separate test tubes containing a 0.1 M solution of their respective nitrate solutions. The results are shown in the table.
Metal | Q(NO3)2 solution | X(NO3)2 solution | Z(NO3)2 solution | A(NO3)2 solution |
Q | Not tested | No reaction | No reaction | No reaction |
X | Coating formed | Not tested | No reaction | No reaction |
Z | Coating formed | Coating formed | Not tested | Coating formed |
A | Coating formed | Coating formed | No reaction | Not tested |
a) Identify the species oxidised in the reaction between Z and X(NO3)2.
[1 mark]
b) Identify the oxidising agent in the reaction between Z and Q(NO3)2.
[1 mark]
c) Determine the products formed from the reaction between Z and A(NO3)2.
[1 mark]
d) Predict the standard reduction potential table for the metals Q, X, Z and A by listing their reduction half-equations from strongest to weakest reducing agent. Explain your reasoning.
[4 marks]
QCAA guide · typeset solution
QCAA sample response and mark allocation
27 | a) | Z | • provides Z [1 mark] | |
b) | Q2+ | • provides Q2+[1 mark] | For Q2+ accept Q in Q(NO3)2 | |
c) | Z(NO3)2(aq) and A(s) | • provides Z(NO3)2(aq) and A(s)[1 mark] | For Z(NO3)2(aq), accept Z2+(aq). | |
d) | Z2+ + 2e− ⇌ Z A2+ + 2e− ⇌ A X2+ + 2e− ⇌ X Q2+ + 2e− ⇌ Q Z can reduce X2+, Q2+ and A2+, therefore it is the strongest reducing agent. X can only reduce Q2+ therefore it is the second weakest reducing agent. Q cannot reduce any metal ions, therefore it is the weakest reducing agent. | • provides half-equations in correct order [1 mark] • provides reasoning for Z as strongest reducing agent [1 mark] Q as weakest reducing agent [1 mark] A as stronger reducing agent than X [1 mark] |
Paper 2: Short response
Question | Sample response | The response: | Notes | |
QCAA sample response and marking criteria reproduced from the official guide.
Compare your working with the guide above.