Chemistry 5070 · O Level · Reactivity series

Reactivity series — practice question

A student compares the reaction of four metals, A, B, C and D, with aqueous copper(II) sulfate. The four metals are each grey solids. The student: • pours $25\,\text{cm}^3$ of aqueous copper(II) sulfate into a beaker and notes its temperature • enters this temperature in Table 2.1 • adds a sample of A to the aqueous copper(II) sulfate • stirs the reaction mixture until the temperature no longer increases • measures the maximum temperature of the mixture and enters this temperature in Table 2.1 • notes any visible change in the appearance of the mixture in the beaker. The student then repeats the experiment three further times, using B, C and D instead of A. The results for D are shown in Fig. 2.1. The results for A, B and C are shown in Table 2.1. Table 2.1 metal | starting temperature / ^{\circ}C | maximum temperature / ^{\circ}C | temperature rise / ^{\circ}C A | 20 | 69.5 | 49.5 B | 24.5 | 46.0 | C | 22.0 | 61.0 | 39.0 D | | |
(a(i))[1]

State the entry in Table 2.1 that the student records to the wrong level of precision.

(a(ii))[3]

The temperatures for D are shown in Fig. 2.1. Enter these temperatures in Table 2.1. Work out and enter the temperature rises for B and D in Table 2.1.

(a(iii))[1]

The equation for the reaction between B and aqueous copper(II) sulfate is given. $\text{B(s)} + \text{CuSO}_4\text{(aq)} \rightarrow \text{BSO}_4\text{(aq)} + \text{Cu(s)}$ Copper(II) sulfate is a blue solution. By the end of the experiment, the student sees a colourless solution, a grey solid and a brown solid. Explain how these observations show that B is in excess in this reaction.

(a(iv))[1]

Using the equation in (a)(iii), give the formula for: • the colourless solution • the grey solid • the brown solid

(b)[2]

Using your results, put A, B, C and D into order of reactivity from most reactive to least reactive. Explain how the results lead to this order.

(c)[1]

A student carries out the experiment again using a fifth metal. This metal is the second most reactive of the five metals. Suggest a temperature increase for this experiment.

(d)[2]

The measured temperature increases are lower than the true values for these experiments. Suggest a reason for this. Describe an improvement to the method that would make the results closer to the true values.

(e)[3]

State and explain the effect on the temperature increase for metal A of using half the concentration of aqueous copper(II) sulfate.

Worked solution & mark scheme

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