Which of the following statements is correct during the electrolysis of…
Which of the following statements is correct during the electrolysis of caustic soda solution using platinum electrodes?
A. Oxygen gas is given off at the cathode
B. Hydrogen gas is given off at the anode
C. Sodium metal is deposited at the cathode
D. Alkalinity at the cathode increases.
Caustic soda solution, which is NaOH dissolved in water, contains the following ions:
During electrolysis, positively charged sodium and hydrogen ions will be attracted to the cathode where a reduction will occur and hydrogen gas (not sodium) will be preferentially discharged. The hydroxide ion will be attracted to the anode where oxidation occurs to give off oxygen gas.
So, oxygen is given off at the anode, while hydrogen will be liberated at the cathode instead of sodium.
Also, at the cathode, the relative concentration of sodium in the solution increases as more hydrogen is given off, making the solution more alkaline especially at this terminal.
Now for the right answer to the above question:
- Option A is incorrect. Oxygen gas is not given off at the cathode, but at the anode instead.
- Option B is incorrect. Hydrogen gas is not given off at the anode, but at the cathode instead.
- C is incorrect. At the cathode, hydrogen gas will be preferentially discharged because it is located further down, when compared with sodium, in the electrochemical series.
- D is the correct answer. Alkalinity will increase because the relative concentration of sodium ion will increase.
You may please note these/this:
- In all electrolysis, oxidation usually occur at the anode to liberate electronegative non-metals like oxygen, chlorine or fluorine depending on available ions and their positions in electrochemical series…
- Reduction on the other hand usually occur at the cathode where electropositive elements like hydrogen and metals will be given off depending on the location of the positive ions in the electrochemical series.
- If hydrogen continues to be liberated at the cathode, there will be growing concentration of left over sodium ions, this makes the remaining solution more alkaline.
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/ culled from 2016 JAMB-UTME Chemistry past question 14 /
Which of the following statements is correct during the electrolysis of... » QuizTablet
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