Question Constellation Sign up for free AQA · GCSE · Chemistry · Higher
Planning a chemical-cell concentration experiment
A student investigated the voltage produced by different pairs of metal electrodes in a chemical cell.
Figure 6 shows the apparatus.
- Place a nickel electrode and an electrode made from a different metal (electrode A) in 1.0 mol/dm³ sodium chloride solution.
- Measure the voltage produced.
- Repeat using different metals for electrode A.
| Electrode A | Symbol of metal | Voltage in volts |
|---|---|---|
| Copper | Cu | −0.59 |
| Magnesium | Mg | 2.12 |
| Nickel | Ni | 0.00 |
| Silver | Ag | −1.05 |
| Zinc | Zn | 0.51 |
- the metal electrodes in Table 3
- 1.0 mol/dm³ sodium chloride solution
- pure water.
The voltage produced by a chemical cell depends on the concentration of the electrolyte solution. Plan an experiment to investigate how the voltage produced by a chemical cell varies with the concentration of the electrolyte solution.
Write your answer first. You can study the marking guidance whenever you need it.
Study the marking See what earns credit and compare it with a full-mark answer.
Marking points
- 1 For full credit, gives a logically sequenced method that would produce valid voltage-versus-concentration results.
- 2 May credit a correct cell setup and voltage measurement.
- 3 May credit systematic dilution using measured volumes and multiple concentrations.
- 4 May credit keeping electrode metals and total electrolyte volume constant.
Full-mark answer
Choose two different metal electrodes and connect them to a voltmeter as in Figure 6. Prepare several sodium chloride concentrations by mixing measured volumes of 1.0 mol/dm³ solution and pure water, using a measuring cylinder, pipette or burette, while keeping the total electrolyte volume constant. Place the same two electrodes into each solution to the same depth and separation, record the voltage, and repeat readings for each concentration before calculating a mean. Plot mean voltage against sodium chloride concentration.
Why this answer loses marks
Change the salt concentration and use different metal electrodes each time.
Changing the electrodes confounds the result; keep the metal pair and solution volume controlled while measuring voltage.