Q1. A solution turns the red litmus paper to blue. Excess addition of which of the following solution would reverse the change?
(i) Lime water
(ii) Baking soda
(iii) Vinegar
(iv) Common salt solution
Answer to the Question:
When a solution turns red litmus paper blue, it indicates that the solution is basic in nature. To reverse this change and turn the blue litmus paper back to red, you would need to add an acidic solution.
Among the options provided:
- (i) Lime water – This is basic and would not reverse the change.
- (ii) Baking soda – This is also basic and would not reverse the change.
- (iii) Vinegar – This is acidic and would reverse the change, turning the blue litmus paper back to red.
- (iv) Common salt solution – This is neutral and would not affect the color of the litmus paper.
Correct Answer: (iii) Vinegar
Explanation:
When vinegar (an acidic solution) is added to the basic solution that turned the red litmus blue, it neutralizes the base, resulting in a solution that is acidic. This causes the blue litmus paper to revert to red, demonstrating the principle of neutralization, where an acid reacts with a base to form water and salt.
Key Concept:
- Litmus Test: A simple way to determine whether a solution is acidic or basic. Red litmus turns blue in basic solutions, while blue litmus turns red in acidic solutions.
This understanding is crucial in chemistry, especially in experiments involving acid-base reactions.