AQA A-level Chemistry RP8 Cell EMF Worksheet

A complete AQA A-level Chemistry Required Practical 8 worksheet: measuring the EMF of an electrochemical cell, with full mark scheme.

Two separate files

• Worksheet (9 pages): the student copy, print-ready in black and white
• Mark scheme (11 pages): the same worksheet completed with every answer written in red, with marks shown, plus teacher and technician notes and marking guidance

Use it during the practical, as a follow-up lesson or as homework. Students who miss the lab can still work through a full set of practice results.

What students do

• Label a zinc-copper cell: electrodes, solutions, salt bridge, voltmeter terminals and the direction of electron flow
• Predict the standard EMF of four cells from a table of standard electrode potentials
• Follow the method, with a “why?” prompt for each key step
• Pick the correct set-up and explain the faults in the other two (a copper wire in place of the salt bridge, and a sodium chloride bridge with a silver half-cell)
• Put the steps of a quick filter-paper comparison of metals in order
• Read three digital voltmeters, including a negative reading, and explain what the minus sign means
• Record their own results, or use a practice data set to find the difference and percentage difference from the standard EMF
• Write conventional cell representations with state symbols
• Calculate percentage uncertainty and decide whether a difference is bigger than the meter’s uncertainty
• Decide how six changes or slips affect the measured EMF (bigger, smaller or no change)
• Explain how the potassium nitrate salt bridge works and which way the ions move
• Answer 8 exam-style questions (21 marks), including a Fe3+/Fe2+ half-cell with a platinum electrode, whether Fe3+ oxidises iodide ions, the standard hydrogen electrode, the alkaline hydrogen-oxygen fuel cell, finding an unknown electrode potential and a 6-mark question on ranking three unknown metals by reducing power
• Finish with an “I can” self-check

For teachers

• Quantities per group, options for the silver half-cell, timings, CPAC opportunities and a safety note for every reagent at the concentration used
• Note on the AQA quick-comparison method used in the ordering task
• Common slips to watch for

All questions are original. This is an independent resource, not endorsed by AQA.