What happens to blue litmus paper in the presence of an alkaline substance?

When blue litmus paper is exposed to an alkaline substance, it remains unchanged. This is because blue litmus paper is specifically designed to indicate the presence of acids and will not react or change color in alkaline conditions.

In an alkaline environment, the pH level is greater than 7, which means that the litmus paper does not undergo any chemical reaction that would alter its color. This property is what makes litmus paper a reliable indicator of acidity and alkalinity. Blue litmus paper remains blue in alkalines, providing a consistent and clear indication that the substance is indeed alkaline.