Understanding Blue Litmus Paper
Blue litmus paper is a common tool used in chemistry to determine the acidity or basicity of a solution. It is an indicator that changes color depending on the nature of the solution it is exposed to.

What Happens When Blue Litmus Paper Remains Unchanged?
- If blue litmus paper does not change color, it indicates that the solution is **neutral** or **basic**.
- A neutral solution has a pH of 7, such as pure water, where the blue litmus paper remains blue.
- In basic solutions (pH greater than 7), blue litmus paper also remains blue, indicating the presence of hydroxide ions (OH⁻).

Why Does This Occur?
- **Chemical Reaction**: Blue litmus paper contains a dye that reacts with hydrogen ions (H⁺). If no H⁺ ions are present in the solution, the dye does not change color.
- **Indicator Function**: Litmus paper is specifically designed to indicate changes in acidity. In the absence of acids, the blue color persists.

Conclusion
- Thus, if a blue litmus paper does not change color, it confirms that the solution is either neutral or basic.
- It is a simple yet effective way to assess the nature of a solution in laboratory experiments and practical applications.