ExpertMedium1 markMultiple Choice
AQA GCSE · Question 07.6 · Chemical changes
Why is hydrogen produced instead of sodium in the electrolysis of aqueous sodium sulfate solution?
Why is hydrogen produced instead of sodium in the electrolysis of aqueous sodium sulfate solution?
Answer options:
A.
Hydrogen is less reactive than sodium.
B.
Hydrogen has the same reactivity as sodium.
C.
Hydrogen is more reactive than sodium.
How to approach this question
In the electrolysis of an aqueous solution, there is a competition at the negative electrode between the metal ion (Na⁺) and the hydrogen ion (H⁺ from water). The rule is: the ion of the less reactive element will be discharged. Compare the reactivity of sodium and hydrogen.
Full Answer
A.Hydrogen is less reactive than sodium.✓ Correct
Hydrogen is less reactive than sodium.
During the electrolysis of an aqueous solution containing a metal salt, there are two types of positive ions that are attracted to the negative electrode (cathode): the metal cations (Na⁺) and hydrogen ions (H⁺) from the water. A rule determines which one is discharged: if the metal is more reactive than hydrogen, then hydrogen gas will be produced. Sodium is a very reactive metal, much more reactive than hydrogen. Therefore, hydrogen ions gain electrons to form hydrogen gas, while the sodium ions remain in the solution.
Common mistakes
✗ Getting the reactivity order of sodium and hydrogen wrong.\n✗ Forgetting the rule about reactivity for electrolysis of aqueous solutions.
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