Which statement about electroplating a copper spoon with silver is correct?
A) Both the anode and cathode are made of carbon.
B) The copper spoon is the anode.
C) Aqueous copper(II) sulfate is the electrolyte.
D) Silver is formed at the negative electrode.
▶️ Answer/Explanation
Ans: D
In electroplating, the object to be plated (copper spoon) must be the cathode (negative electrode), where reduction occurs and silver ions gain electrons to form silver metal. The anode is typically made of the plating metal (silver in this case), not carbon. The electrolyte must contain ions of the plating metal (silver nitrate solution would be used, not copper(II) sulfate). Therefore, the only correct statement is that silver is formed at the negative electrode (cathode).
What is the definition of electrolysis?
A) the formation of a positive ion by the removal of electrons using an electric current
B) the decomposition of an ionic compound, when molten or in aqueous solution, by the passage of an electric current
C) the substance containing ions through which an electric current can pass
D) the coating of a metal with a different metal by passing an electric current through an aqueous solution of an ionic salt
▶️ Answer/Explanation
Ans: B
Electrolysis is specifically defined as the decomposition of an ionic compound (when molten or in aqueous solution) by passing an electric current through it. This process causes the compound to break down into its constituent elements or simpler compounds. Option A describes ionization, option C describes an electrolyte, and option D describes electroplating, which is an application of electrolysis but not its definition.
Molten sodium sulfide, Na2S, is electrolysed using inert electrodes.
Which row identifies the product at each electrode?
| cathode | anode | |
|---|---|---|
| A | sodium | sulfur |
| B | sulfur | sodium |
| C | hydrogen | sulfur |
| D | sodium | hydrogen |
▶️ Answer/Explanation
Ans: A
When molten Na2S is electrolyzed:
At the cathode (negative electrode): Na+ ions are reduced to sodium metal because sodium ions are more easily reduced than sulfide ions.
At the anode (positive electrode): S2- ions are oxidized to sulfur because there are no other ions present to be oxidized (the electrodes are inert).
Hydrogen isn’t produced because the compound is molten (no water present) and we’re not dealing with aqueous solutions.
Three substances are listed.
- solid copper
- aqueous sodium bromide
- solid lead(II) bromide
Which substances conduct electricity?
A) 1, 2 and 3
B) 1 and 2 only
C) 1 and 3 only
D) 2 and 3 only
▶️ Answer/Explanation
Ans: B
To determine which substances conduct electricity, we need to consider their physical states and bonding:
1. Solid copper is a metal, so it conducts electricity due to its delocalized electrons.
2. Aqueous sodium bromide conducts electricity because it’s an ionic compound dissolved in water, forming free-moving ions.
3. Solid lead(II) bromide doesn’t conduct electricity in solid state as the ions are fixed in position, though it would conduct when molten or dissolved.
Therefore, only substances 1 and 2 conduct electricity under the given conditions.