A blank nine-step write-up with the correct table headings. Print it for a real lesson and fill it in by hand. See the specimen lab book
Blank write-up: Electrolysis
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Study Hack Lab
RP 3 · Chemistry
Electrolysis
Write-up template
Name
Date
Course
GCSE Chemistry
Board and specification
AQA GCSE Chemistry (8462), 4.4.3.4AQA GCSE Combined Science: Trilogy (8464), 5.4.3.4Apparatus and techniques: AT 3, AT 7, AT 8
Class and teacher
Aim
Find out what forms at each electrode when four salt solutions are electrolysed with graphite (inert) electrodes, test the gases, and use the results to test your hypothesis.
Contents
Plan and risk assessment
Apparatus
Method
Results
Graph
Analysis
Conclusion and evaluation
Make safe and clear up
A blank write-up for use in a real lesson. The headings follow the AQA required practical; the readings are yours to take. Layout v1, practical v2. Original material; not affiliated with AQA, which has not reviewed it.
1 Plan and risk assessment
In a solution the ions move, not electrons: positive ions to the negative electrode, negative ions to the positive. At the negative electrode the less reactive of the metal and hydrogen forms. At the positive electrode a halide gives the halogen; otherwise hydroxide ions from the water give oxygen.
Cu²⁺ + 2e⁻ → Cu 2Cl⁻ → Cl₂ + 2e⁻
Variables
Independent (you change)
Dependent (you measure)
Control (you keep the same)
Prediction
Your hypothesis for the negative electrode: which statement do you think is right?
Your hypothesis for the positive electrode: which statement do you think is right?
When sodium sulfate solution is electrolysed, how will the volume of hydrogen compare with the volume of oxygen?
Risk assessment
Hazard
Harm it could cause
Control
2 Apparatus
Safety goggles Protect your eyes from splashes of the solutions.
Low-voltage power pack (d.c.) Set to 4 V: pushes the current through the solution.
Ammeter (digital multimeter, 10 A range) (resolution 0.01 A) Shows that a current is flowing, and how big it is.
Leads with crocodile clips Connect the rods to the power pack, red to positive.
100 cm³ beaker, Petri-dish lid and two graphite rods The cell: the lid holds the rods apart.
Copper(II) chloride, copper(II) sulfate, sodium chloride and sodium sulfate solutions, 0.5 mol/dm³ The four electrolytes, 50 cm³ each.
Blue litmus paper, tweezers and a wash bottle Tests for chlorine; the water dampens the paper and rinses the rods.
Gas-collection cell with graphite rods through its base Part B: the gases collect over each rod.
Two 10 cm³ measuring cylinders, clamped upside down (resolution 0.2 cm³) Measure the volume of each gas.
Two test tubes The other way to collect the gases (no scale).
Stopclock (resolution 1 s) Times the readings every minute.
Wooden splints and a Bunsen burner A lit splint tests for hydrogen; a glowing one for oxygen.
Copper residues bottle Copper solutions go here, not down the sink.
3 Method
Write numbered steps someone else could follow. Say what you measure, with which instrument, and how you keep it a fair test.
4 Results
The table is drawn before you measure. Record each reading to the resolution of the instrument, then work out the mean of your repeats, leaving out any anomaly.
Part A: four solutions, 4 V, 5 minutes each · Litmus: damp blue litmus held in the gas just above the positive electrode.
Solution
Current in A
Positive electrode
Blue litmus
Negative electrode after 5 min
CuCl₂
CuSO₄
NaCl
Na₂SO₄
Part B: sodium sulfate solution, gases collected in 10 cm³ measuring cylinders
Time in min
Volume of hydrogen in cm³
Volume of oxygen in cm³
1
2
3
4
5
5 (repeat)
Part B: testing the gases
Test
Result
Lit splint, gas from the negative electrode
Glowing splint, gas from the positive electrode
Anomalies
Ring any anomalous result. Say what probably went wrong and whether you repeated it.
5 Graph
Volume of gas against time · Choose your axes: the independent variable goes on the x-axis. Label each axis with the quantity and unit.
6 Analysis
The product at each electrode
Answer
Half equations
Answer
Gradient of the hydrogen line (rate of hydrogen production)
Answer
The ratio of the gases
ratio = hydrogen collected from 1 to 5 min ÷ oxygen collected from 1 to 5 min
Answer
Moles of hydrogen (Chemistry only, Higher)
amount in mol = volume in dm³ ÷ 24
Answer
7 Conclusion and evaluation
Conclusion
Conclusion: what do your results show? Use your own numbers.
Sources of error
For each, say whether it is systematic or random, and how it affected your results.
Copper left on the negative rod from an earlier solution
Dry litmus, or litmus held away from the electrode
Some of each gas dissolves in the solution at the start (oxygen more than hydrogen)
Collecting the gases in test tubes, which have no scale
Reading the upturned scale from above (parallax)
A loose crocodile clip
Bubbles sticking to the rods and the cylinder walls
Improvement
How could you improve the method? Say why it would help.
8 Make safe and clear up
Switch off the power pack before you unclip the leads
Take out the rods, then wipe the copper off them and rinse them
Check both copper solutions went into the residues bottle, never down the sink, and put its lid on
Rinse the sodium solutions away with plenty of water. Put the splints out in water, then bin them with the litmus
Keep the room ventilated until any smell of chlorine has gone