Question

During electrolysis of water, identify the correct combination.

• A. At cathode : 01-part hydrogen gas; At anode : 02-part oxygen gas.
• B. At cathode : 02-part hydrogen gas; At anode : 01-part oxygen gas.
• C. At cathode : 01-part oxygen gas; At anode : 02-part hydrogen gas.
• D. At cathode : 02-part oxygen gas; At anode : 01-part hydrogen gas.

Hint:

Remember the memory keys:
- An-Ox: Anode undergoes Oxidation (Oxygen is produced at Anode).
- Cat-Red: Cathode undergoes Reduction (Hydrogen is produced at Cathode).
- Water formula is \(\text{H}_2\text{O}\), so Hydrogen volume is twice (\(2\times\)) that of Oxygen.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question asks for the correct products and their respective volume ratios collected at the cathode and anode during the electrical decomposition (electrolysis) of water.

Step 2: Key Formula or Approach: The chemical decomposition of water by electricity is represented by the equation:
\[ 2\text{H}_2\text{O(l)} \xrightarrow{\text{Electricity}} 2\text{H}_2\text{(g)} + \text{O}_2\text{(g)} \]

Step 3: Detailed Explanation:

• Water decomposes into hydrogen gas (\(\text{H}_2\)) and oxygen gas (\(\text{O}_2\)) during electrolysis.

• Reaction at Cathode (Reduction): Hydrogen ions (\(\text{H}^+\)) gain electrons at the negative electrode (cathode) to form hydrogen gas:
\[ 4\text{H}^+\text{(aq)} + 4e^- \to 2\text{H}_2\text{(g)} \]

• Reaction at Anode (Oxidation): Hydroxide/water molecules lose electrons at the positive electrode (anode) to form oxygen gas:
\[ 2\text{H}_2\text{O(l)} \to \text{O}_2\text{(g)} + 4\text{H}^+\text{(aq)} + 4e^- \]

• According to Avogadro's law, the molar ratio of gases is directly proportional to their volumes at the same temperature and pressure.

• The stoichiometry of the overall reaction shows that for every 2 molecules of water decomposed, we obtain 2 volumes (or parts) of hydrogen gas at the cathode and 1 volume (or part) of oxygen gas at the anode.

• Thus, the volume of hydrogen gas collected is double the volume of oxygen gas.


Step 4: Final Answer:
The correct combination is: At cathode: 02-part hydrogen gas; At anode: 01-part oxygen gas.