Electrolysis (OCR GCSE Combined Science A (Gateway): Chemistry): Flashcards
Exam code: J250
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Define electrolysis.
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Cards in this collection (36)
Define electrolysis.
Electrolysis is the process in which an electric current is passed through a molten or dissolved ionic compound, causing it to decompose into its elements.
True or False?
Solid ionic compounds can conduct electricity.
False.
Electrolysis works on ionic compounds because the process requires ions that are free to move and carry charge. In the solid state, ions are fixed in a lattice. When molten or dissolved, they are mobile and can migrate to electrodes.
What is an electrolyte?
An electrolyte is a liquid or solution that can conduct electricity — it is an ionic compound in molten or dissolved form.
Why must an ionic compound be molten or dissolved before it can undergo electrolysis?
In the solid state, ions are held in fixed positions in a lattice and cannot move. The ionic compound must be molten or dissolved so that the ions are free to move and carry charge to the electrodes, allowing the electric current to flow.
During electrolysis, positive ions migrate towards the .......... and negative ions migrate towards the ............
During electrolysis, positive ions migrate towards the cathode and negative ions migrate towards the anode.
What are the products formed at each electrode when molten lead(II) bromide undergoes electrolysis?
At the cathode, lead metal is produced. At the anode, bromine gas is produced. The positive metal ion is discharged at the cathode and the negative non-metal ion is discharged at the anode.
True or False?
Covalent compounds can undergo electrolysis.
False.
Covalent compounds cannot undergo electrolysis when dissolved in water because they do not form ions in solution. Electrolysis requires free-moving ions to carry charge. Covalent substances dissolve as molecules, not ions.
Define anode.
The anode is the positive electrode in an electrolysis cell, towards which negatively charged anions migrate.
When a molten binary ionic compound undergoes electrolysis, the .......... is produced at the cathode and the .......... is produced at the anode.
When a molten binary ionic compound undergoes electrolysis, the metal is produced at the cathode and the non-metal is produced at the anode.
Why must electrodes used in electrolysis be inert?
Inert electrodes such as graphite or platinum are used so that they do not react with the electrolyte, ensuring only the intended products are formed at each electrode.
What extra ions are always present in the electrolysis of an aqueous solution, and where do they come from?
H+ and OH- ions are always present. They come from the partial dissociation of water molecules in the solution.
At the cathode during electrolysis of an aqueous solution, .......... is produced if the metal ion is more reactive than hydrogen, otherwise .......... is produced.
At the cathode during electrolysis of an aqueous solution, hydrogen gas is produced if the metal ion is more reactive than hydrogen, otherwise the metal is produced.
True or False?
Oxygen is always produced at the anode during electrolysis of an aqueous solution.
False.
At the anode, halide ions (e.g. Cl⁻, Br⁻) are oxidised and discharged, releasing the corresponding halogen as a gas. The halogen produced depends on which halide ions are present in the solution.
What is produced at the cathode when copper sulfate solution is electrolysed using inert electrodes?
Copper metal deposits at the cathode. Copper is less reactive than hydrogen, so copper ions are discharged in preference to hydrogen ions.
What is electroplating?
Electroplating is a process that uses electrolysis to coat an object with a thin layer of a different metal, such as coating steel cutlery with silver.
In electroplating, what roles do the cathode, anode, and electrolyte each play?
The cathode is the object to be coated. The anode is made from the coating metal. The electrolyte is a solution containing ions of the coating metal.
True or False?
Inert electrodes take part in electrolysis reactions.
False.
Graphite electrodes are used as inert electrodes in electrolysis because they do not react with the electrolyte or products. This ensures they do not interfere with the products formed at each electrode.
When purifying copper by electrolysis, the anode is made of .......... copper and the cathode is made of .......... copper.
When purifying copper by electrolysis, the anode is made of impure copper and the cathode is made of pure copper.
Why does the anode decrease in mass and the cathode increase in mass during the purification of copper?
At the anode, copper atoms lose electrons and dissolve into the electrolyte as ions, so the anode loses mass. At the cathode, copper ions from the electrolyte gain electrons and deposit as copper atoms, so the cathode gains mass.
Define oxidation in terms of electrons.
Oxidation is the loss of electrons by a substance during a chemical reaction.
Define reduction in terms of electrons.
Reduction is the gain of electrons by a substance during a chemical reaction.
True or False?
Oxidation occurs at the cathode during electrolysis.
False.
Oxidation occurs at the anode, where negatively charged ions lose electrons. Reduction occurs at the cathode, where positive ions gain electrons.
What happens to a negatively charged ion when it reaches the anode during electrolysis?
At the anode, the negatively charged ion loses electrons to the electrode. This is oxidation. The ion is discharged and forms a neutral substance.
At the cathode, positive ions .......... electrons and are ...........
At the cathode, positive ions gain electrons and are reduced.
What does it mean for an ion to be discharged at an electrode?
An ion is discharged when it gains or loses electrons at an electrode, converting from a charged ion into a neutral substance that is released as a product.
True or False?
During electrolysis, both oxidation and reduction occur at the same time.
True.
At the cathode (negative electrode), positive ions are reduced by gaining electrons. At the anode (positive electrode), negative ions are oxidised by losing electrons.
Why is the process at the anode described as oxidation during electrolysis?
The process at the anode is oxidation because the negative ions arriving at the anode lose electrons to the electrode, and the loss of electrons defines oxidation.
(Higher Tier Only) What is the purpose of a half equation in electrolysis?
A half equation shows the oxidation or reduction reaction at a single electrode, including the number of electrons gained or lost by the ions.
(Higher Tier Only) Complete the cathode half equation for the electrolysis of molten lead(II) bromide:\n\nPb2+ + .......... ⟶ Pb
Pb2+ + 2e- ⟶ Pb
Lead ions gain two electrons at the cathode and are reduced to lead metal.
True or False?
(Higher Tier Only) In a half equation, only the number of atoms must be balanced, not the charges.
False.
In a half equation, both the number of atoms and the charges on each side must be balanced.
(Higher Tier Only) Write the anode half equation for the electrolysis of molten lead(II) bromide.
2Br- ⟶ Br2 + 2e-
Bromide ions lose electrons at the anode (oxidation) and are discharged as bromine gas.
(Higher Tier Only) What is a half equation?
A half equation is an equation that shows the reaction at one electrode only, representing the gain or loss of electrons by ions during electrolysis.
(Higher Tier Only) Complete the cathode half equation for the electrolysis of molten aluminium oxide:\n\nAl3+ + .......... ⟶ Al
Al3+ + 3e- ⟶ Al
Aluminium ions gain three electrons at the cathode and are reduced to aluminium metal.
(Higher Tier Only) Why does the anode half equation for bromide ions show two bromide ions rather than one?
Bromine exists as a diatomic molecule (Br2), so two Br- ions must lose one electron each to form one molecule of Br2. This balances both atoms and charges.
True or False?
(Higher Tier Only) The half equation Al3+ + 3e- ⟶ Al represents oxidation.
False.
This half equation represents reduction. Aluminium ions gain electrons at the cathode, which is reduction, not oxidation.
(Higher Tier Only) What is the anode half equation for the electrolysis of molten aluminium oxide?
2O2- ⟶ O2 + 4e-
Oxide ions lose electrons at the anode (oxidation) and are discharged as oxygen gas.
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