3.4 Electrolysis
Problems Worksheet
1. Explain how electrolysis differs from the process which occurs in a voltaic cell.
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2. A group of students set up an electrolytic cell with graphite electrodes in molten potassium bromide.
a. Draw a diagram of the electrolytic cell. Include in your diagram the anode, cathode, voltage
supply, positive and negative terminals, electron flow and the flow of ions in the liquid.
b. Write equations for the reactions occurring at each electrode and an overall reaction with the
voltage required. Include state symbols.
c. Write an observation for the reaction.
d. The students have calculated the required voltage and are confused when they do not see a
reaction. Explain why this could be.
e. Why would no reaction occur if the KBr was in the solid state?
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3. An electrolytic cell is set up with graphite electrodes and a solution of 1.00 mol.L‒1 nickel iodide.
a. Draw a diagram of the electrolytic cell. Include in your diagram the anode, cathode, voltage
supply, positive and negative terminals, electron flow and the flow of ions in the liquid.
b. Write equations for the reactions occurring at each electrode, and the overall equation and
voltage. Include the states of the reactants and products.
c. Write an observation for the process.
d. Why are graphite electrodes often used in electrolysis?
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4. Use the table of standard reduction potentials to write the likely reactions at each electrode, and an
overall equation for electrolysis of the following:
a. A solution of silver nitrate with graphite electrodes.
b. A solution of iron(II) sulfate with iron electrodes.
c. A solution of sodium fluoride with copper electrodes.
d. A mixture of magnesium sulfate and zinc nitrate with graphite electrodes.
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5. It is often observed when doing electrolysis experiments that the reactions observed do not match the
predictions made using the table of standard reduction potentials. Explain why this could be.
6. The diagram shows a metal spoon being plated with silver. Explain the process which is occurring:
OpenStax, Chemistry. OpenStax CNX. 2017 CC 4.0
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7. Electrorefining can be used to purify copper. The blister copper to be purified is between 97% and 99%
copper. The remaining material in the blister copper are impurities such as iron, zinc, nickel, silver and
gold. Correctly preformed electrorefining should yield copper with a purity of close to 99.97%.
To perform the procedure the impure blister copper is connected to the positive terminal of the power
supply, making it the anode, and a sheet of pure copper is used as the cathode.
a. Write equations for all the possible reactions at the anode, given the impurities contained in the
blister copper.
b. If just enough voltage is supplied to oxidise the copper metal, which other metals in the blister
copper will be oxidised?
c. Explain how pure copper is produced at the cathode.
d. The electrolyte used for this reaction is usually copper(II) sulfate. Explain the effect it would have
if copper(II) chloride solution was used as the electrolyte.
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