A student investigated the electrolysis of different substances.
Figure 6 shows the apparatus.
Figure 6
Explain why electrolysis would not take place in the apparatus shown in Figure 6.
[2 marks]
ANSWER
Solid zinc chloride does not conduct electricity because ions cannot move in the solid i.e. ions can only move in liquid / solution; therefore zinc chloride needs to be in solution or molten form.
Explain why graphite conducts electricity.
Answer in terms of the structure and bonding in graphite.
[3 marks]
ANSWER
Each carbon atom forms 3 (three) covalent bonds leaving behind one electron per carbon atom as delocalized so these electrons carry charge through the graphite and these electrons move through the structure.
The student investigated how the volume of gases produced changes with time in the electrolysis of sodium chloride solution.
Figure 7 shows the apparatus.
Figure 7
The student made an error in selecting the apparatus for this investigation. How should the apparatus be changed?
Give one reason for your answer. [2 marks]
ANSWER
Use measuring cylinders instead of test tubes because test tubes cannot measure volume as test tubes have no graduations / scale.
Another student used the correct apparatus.
This student measured the volumes of gases collected every minute for 20minutes.
Figure 8 shows the student’s results.
Figure 8
Describe the trends shown in the results.
Use values from Figure 8. [3 marks]
ANSWER
The volume of hydrogen collected is directly proportional to the time;
The rate of collection of hydrogen is 0.45 (cm3/min);
Up to 8 minutes chlorine is collected at an increasing rate;
After 8 minutes the rate of collection of chlorine is the same as that of hydrogen i.e. after 8 minutes the rate of collection of chlorine is 0.45 (cm3/min).
The number of moles of each gas produced at the electrodes is the same. No gas escapes from the apparatus.
Suggest one reason for the difference in volume of each gas collected. [1 mark]
ANSWER
Chlorine reacts with water or chlorine dissolves in the solution.
Calculate the amount in moles of chlorine collected after 20 minutes. Use Figure 8.
The volume of one mole of any gas at room temperature and pressure is 24.0 dm3 Give your answer in standard form. [3 marks]
ANSWER
