Question

When a blue litmus paper is put in an acidic Solution, it turns red. Can the red litmus which has been formed used to indicate basicity?

In other words, can litmus paper which has changed its colour once be reused?

Answer 1

The reaction
litmus ( acid) red ↔ litmus (basic) blue
is a reversible reaction. If you place blue litmus paper in a weak acid solution and it turns red ,there is no problem in rinsing the acid away from the paper and using it in a weak basic solution where it will turn blue.

Allow the litmus paper to dry. Once you have used the litmus paper, it will be wet. Before it can be reused, you should allow the paper to dry. Set it out at room temperature for a few hours, and store it as dry litmus paper.

Reuse unchanged litmus paper. If the paper was unchanged by the reaction, it can be reused as the same color.

Reuse changed litmus paper as the new color. If your paper came in contact with a sample and changed colors, you can now use it as the color that it has become. Red litmus paper that turned blue can be reused as blue litmus paper and viceversa