Question

During charging, the electrolyte of a lead acid battery becomes

• A. stronger
• B. weaker
• C. diluted with water
• D. None of these

Hint:

During the charging process of a lead-acid battery, the concentration of sulfuric acid in the electrolyte increases, making it stronger.

Answer 1

The Correct Option is A

Step 1: Understanding the process of charging.
In a lead-acid battery, during the charging process, the lead sulfate formed on the plates during discharge is converted back into lead dioxide and lead, and sulfuric acid is regenerated in the electrolyte.
Step 2: Effect on electrolyte concentration.
As the battery charges, the concentration of sulfuric acid in the electrolyte increases, making it stronger.
Step 3: Conclusion.
Thus, during charging, the electrolyte becomes stronger, which corresponds to option (A).

Answer 2

We can answer this by looking directly at the chemical reaction that occurs during charging. During discharge, the reaction at both plates is: \[ \text{Pb} + \text{PbO}_2 + 2\text{H}_2\text{SO}_4 \rightarrow 2\text{PbSO}_4 + 2\text{H}_2\text{O}. \] Charging drives this reaction in reverse: \[ 2\text{PbSO}_4 + 2\text{H}_2\text{O} \rightarrow \text{Pb} + \text{PbO}_2 + 2\text{H}_2\text{SO}_4. \] This reverse reaction consumes water and regenerates sulfuric acid, directly increasing the acid concentration in the electrolyte. Let's check each option against this reaction.

1. Stronger: Since charging regenerates sulfuric acid and consumes water, the acid concentration (and specific gravity) rises, making the electrolyte stronger — matching the reverse reaction exactly.
2. Weaker: A weaker electrolyte would result from acid being consumed and water being produced, which is what happens during discharge, not charging.
3. Diluted with water: Dilution with water would also lower the acid concentration, again describing the discharge process, not charging, where water is consumed instead of produced.
4. None of these: Since the chemical reaction clearly shows the electrolyte becoming stronger during charging, this option is ruled out.

The reversed charging reaction confirms that the electrolyte becomes stronger.

Therefore, the correct answer is stronger.