Electrolysis

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

Question 21

A student investigates the electrolysis of copper(II) sulfate solution using copper electrodes which take part in the reaction.

She uses this method:

Weigh two clean strips of copper.
Use one strip as the positive electrode and the other as the negative electrode.
After electrolysis, wash the strips of copper with ethanol (a liquid that boils at $78∘C78^\circ\text{C}$ ).
Dry the strips of copper and reweigh them.

The ionic half-equations for the reactions at the electrodes are:

Positive electrode: $Cu(s)−2e−→Cu2+(aq)\text{Cu}(s) - 2\text{e}^- \rightarrow \text{Cu}^{2+}(aq)$
Negative electrode: $Cu2+(aq)+2e−→Cu(s)\text{Cu}^{2+}(aq) + 2\text{e}^- \rightarrow \text{Cu}(s)$

Suggest why the copper strips would dry more quickly when washed with ethanol rather than with water.

[1]

The student's results are shown in the table:

Electrode	Mass of electrode before electrolysis in $g\text{g}$	Mass of electrode after electrolysis in $g\text{g}$
Positive electrode	$18.65$	$17.15$
Negative electrode	$14.25$	$15.57$

Calculate the increase in mass, in grams, of the negative electrode.

[1]

Suggest two reasons why the increase in mass of the negative electrode was less than the decrease in mass of the positive electrode.

[2]

Another student investigated the effect of changing the electrical charge, in faradays, passed during the electrolysis. One faraday is the electrical charge of one mole of electrons. Their results are shown in the table:

Experiment	1	2	3	4	5	6	7	8	9
Electrical charge in faradays	0.02	0.04	0.06	0.08	0.10	0.12	0.14	0.16	0.18
Increase in mass in $g\text{g}$	0.64	1.28	1.92	2.56	2.40	3.84	4.48	5.12	5.76

Identify which experiment gave an anomalous result.

[1]

Suggest why a line of best fit plotted for this data should go through the origin $(0, 0)$ .

[1]

Explain how the data shows that the increase in mass is directly proportional to the electrical charge passed.

[2]

Calculate the expected increase in mass, in grams, of the negative copper electrode if an electrical charge of $0.22$ faradays was passed.

[1]

Electrode

Mass of electrode before electrolysis in

g\text{g}

Mass of electrode after electrolysis in

g\text{g}

Positive electrode

18.65

17.15

Negative electrode

14.25

15.57

Experiment

Electrical charge in faradays

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

Increase in mass in $g\text{g}$

0.64

1.28

1.92

2.56

2.40

3.84

4.48

5.12

5.76

Electrolysis

Question 21

Electrolysis Questions

Electrolysis

Question 21

Electrolysis Questions