4.1 Electrolysis (Cambridge (CIE) O Level Chemistry): Flashcards
Exam code: 5070
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Define electrolysis.
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Cards in this collection (43)
Define electrolysis.
Electrolysis is the decomposition of a molten or dissolved ionic compound by passing an electric current through it.
True or False?
A solid ionic compound cannot conduct electricity because its ions are in fixed positions and cannot move.
True.
A solid ionic compound cannot conduct electricity because its ions are held in fixed positions in the lattice. Electrolysis requires mobile ions, which are only present when the compound is molten or dissolved.
Ionic compounds can undergo electrolysis when ______ or dissolved in water, but not in the ______ state.
Ionic compounds can undergo electrolysis when molten or dissolved in water, but not in the solid state.
Why can covalent compounds not be electrolysed?
Covalent compounds cannot be electrolysed because they have no free ions to carry charge. Electrolysis requires mobile ions, which are only present in molten or dissolved ionic compounds.
During electrolysis, ______ or hydrogen gas is always produced at the cathode.
During electrolysis, a metal or hydrogen gas is always produced at the cathode. These are elements that form positive ions (cations).
True or False?
During electrolysis, negatively charged ions move towards the cathode.
False.
During electrolysis, negatively charged ions (anions) move towards the anode (positive electrode). Positively charged ions (cations) move towards the cathode (negative electrode).
In electrolysis, ______ are the charge carriers in the external circuit, while ______ are the charge carriers in the electrolyte.
In electrolysis, electrons are the charge carriers in the external circuit, while ions are the charge carriers in the electrolyte.
In electrolysis, is the substance formed at the cathode the ion or the neutral element?
The substance formed at the cathode is always the neutral element, not the ion.
For example, when lead(II) bromide is electrolysed, lead metal is produced at the cathode, not lead(II) ions.
In the electrolysis of a molten binary ionic compound, the ______ is always produced at the cathode and the ______ is always produced at the anode.
In the electrolysis of a molten binary ionic compound, the metal is always produced at the cathode and the non-metal is always produced at the anode.
True or False?
When molten lead(II) bromide is electrolysed, bromine gas is produced at the anode.
True.
Bromide ions (Br-) are negatively charged and move to the anode, where they lose electrons to form bromine gas. It appears as a brown gas.
When lead(II) bromide is electrolysed, a ______ solid deposits on the surface of the cathode. This substance is ______.
When lead(II) bromide is electrolysed, a grey solid deposits on the surface of the cathode. This substance is lead metal.
How do you predict the products at each electrode when a molten binary ionic compound is electrolysed?
Identify the two ions present. The positive ion (cation) moves to the cathode and is discharged as a metal. The negative ion (anion) moves to the anode and is discharged as a non-metal.
True or False?
Graphite is used as an electrode in electrolysis because it is a good conductor and has a low melting point.
False.
Graphite is used because it is inert (does not react with the electrolyte), has good electrical conductivity, and has a high melting point, not a low one.
What products are formed when molten potassium chloride is electrolysed?
Potassium metal is produced at the cathode (from K+ ions gaining electrons) and chlorine gas is produced at the anode (from Cl- ions losing electrons).
The electrolysis of concentrated sodium chloride solution produces ______ at the cathode and ______ at the anode.
The electrolysis of concentrated sodium chloride solution produces hydrogen at the cathode and chlorine at the anode. Sodium hydroxide solution is also produced.
Why is hydrogen, not sodium, produced at the cathode during the electrolysis of aqueous sodium chloride?
Hydrogen is produced because H+ ions are less reactive than Na+ ions and are preferentially discharged at the cathode.
True or False?
Chlorine gas produced at the anode during electrolysis is identified by holding a lighted splint near the gas, which causes a 'pop'.
False.
Chlorine is identified by holding damp litmus paper near the gas — it bleaches the litmus paper. A 'pop' with a lighted splint is the test for hydrogen.
How would you confirm that oxygen gas is being produced at the anode during electrolysis?
Hold a glowing splint in the gas. If the splint relights, the gas is oxygen.
When dilute sulfuric acid is electrolysed, ______ gas is produced at the cathode and ______ gas is produced at the anode.
When dilute sulfuric acid is electrolysed, hydrogen gas is produced at the cathode and oxygen gas is produced at the anode.
True or False?
If a gas from the cathode during electrolysis burns with a squeaky 'pop' when a lighted splint is held to it, the gas is hydrogen.
True.
The squeaky 'pop' is the characteristic test for hydrogen gas — it burns rapidly in the presence of oxygen in air.
Chlorine from brine electrolysis is used to make ______, and sodium hydroxide is used to make ______ and detergents.
Chlorine from brine electrolysis is used to make bleach, and sodium hydroxide is used to make soap and detergents.
In the electrolysis of an aqueous solution, water molecules dissociate to produce additional ______ (H+) and hydroxide (OH-) ions that also take part in the process.
In the electrolysis of an aqueous solution, water molecules dissociate to produce additional hydrogen (H+) and hydroxide (OH-) ions that also take part in the process.
True or False?
In the electrolysis of aqueous sodium sulfate, sodium metal is produced at the cathode.
False.
Sodium is more reactive than hydrogen, so H+ ions are preferentially discharged at the cathode. Hydrogen gas is produced, not sodium metal.
When aqueous copper sulfate is electrolysed with graphite electrodes, ______ metal is deposited at the cathode and ______ gas is produced at the anode.
When aqueous copper sulfate is electrolysed with graphite electrodes, copper metal is deposited at the cathode and oxygen gas is produced at the anode.
True or False?
When copper electrodes are used to electrolyse copper sulfate, the cathode gains mass and the anode loses mass by the same amount.
True.
Copper atoms at the anode are oxidised to Cu2+ ions, which migrate to the cathode and are reduced back to copper metal. The Cu2+ concentration in solution stays constant.
In the electrolysis of aqueous solutions, what determines whether a halogen or oxygen is produced at the anode? {align=center}
If halide ions (Cl-, Br-, I-) are present in sufficient concentration, the halogen is produced at the anode. If no halide ions are present, or the solution is dilute, oxygen is produced instead.
With copper electrodes in copper sulfate electrolysis, the anode ______ in mass as copper ionises, while the cathode ______ in mass as copper ions are deposited.
With copper electrodes in copper sulfate electrolysis, the anode decreases in mass as copper ionises, while the cathode increases in mass as copper ions are deposited.
Why is copper, not hydrogen, produced at the cathode during the electrolysis of aqueous copper sulfate? {align=center}
Copper is less reactive than hydrogen, so Cu2+ ions are preferentially discharged at the cathode over H+ ions. Less reactive ions are discharged in preference to more reactive ones.
True or False?
During the electrolysis of copper sulfate with copper electrodes, the cathode simply gets larger and the electrolyte gradually loses its blue colour.
False.
The cathode gets coated with a pink solid (copper deposits), not just “larger”. The electrolyte stays blue because the Cu2+ concentration remains constant — copper dissolving from the anode replaces what is deposited at the cathode.
In electrolysis, ______ is the loss of electrons and ______ is the gain of electrons.
In electrolysis, oxidation is the loss of electrons and reduction is the gain of electrons.
True or False?
At the anode, positively charged ions lose electrons and are oxidised.
False.
At the anode, negatively charged ions (anions) lose electrons and are oxidised. At the cathode, positively charged ions (cations) gain electrons and are reduced.
In ionic half equations, the cathode reaction shows ions ______ electrons, which is called ______.
In ionic half equations, the cathode reaction shows ions gaining electrons, which is called reduction.
Why must charges balance in an ionic half equation?
Charge must be conserved in any reaction. The number of electrons lost by one species must equal the number gained by another, so both sides of the half equation must have the same total charge.
True or False?
The OIL RIG mnemonic stands for "Oxidation Is Loss, Reduction Is Gain" of electrons.
True.
OIL RIG is a memory aid: oxidation is the loss of electrons (OIL) and reduction is the gain of electrons (RIG).
Write the ionic half equation for the formation of chlorine gas at the anode during electrolysis.
2Cl- → Cl2 + 2e-. Chloride ions each lose one electron and are oxidised to form chlorine gas. Electrons appear on the right (product) side for oxidation.
True or False?
The ionic half equation for copper depositing at the cathode is: Cu2+ + 2e- → Cu.
True.
Copper ions gain 2 electrons at the cathode and are reduced to copper metal. Reduction always shows electrons on the left (reactant) side of the half equation.
Define electroplating.
Electroplating is a process in which the surface of one metal is coated with a layer of a different metal using electrolysis.
True or False?
Electroplating can improve an object's resistance to corrosion and its appearance.
True.
Electroplating is used to coat metals with more resistant materials (e.g. chromium or nickel) to prevent corrosion, and with decorative metals (e.g. silver) to improve appearance.
In electroplating, the ______ is made from the pure plating metal, and the object to be coated is connected as the ______.
In electroplating, the anode is made from the pure plating metal, and the object to be coated is connected as the cathode.
What must the electrolyte contain in an electroplating cell, and why?
The electrolyte must be an aqueous solution of a soluble salt of the plating metal. This ensures ions of that metal are present in solution to be discharged and deposited at the cathode.
When iron is electroplated with tin, the ______ is iron and the ______ is tin. The electrolyte is tin(II) chloride solution.
When iron is electroplated with tin, the cathode is iron and the anode is tin. The electrolyte is tin(II) chloride solution.
Write the ionic half equations for both electrodes during the tin plating of iron.
Anode: Sn (s) → Sn2+ (aq) + 2e- (tin atoms are oxidised).
Cathode: Sn2+ (aq) + 2e- → Sn (s) (tin ions are reduced and deposited on the iron).
True or False?
If a steel key fails to get coated during copper electroplating, increasing the electric current will solve the problem.
False.
If the key is not getting coated, the most likely cause is that it is connected to the wrong terminal. The object to be plated must be at the cathode (negative). The fix is to reverse the electrical connections.
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