Question

You are provided with three test tubes A, B, and C which contain distilled water, acidic solution and basic solution respectively. If you are given blue litmus paper only, how will you identify the contents of each test tube?

Answer 1

We have to know that litmus paper is a kind of pH paper which is prepared using natural dyes that are obtained from lichens. We can perform a litmus test by keeping a small drop of sample on colored paper. We can use litmus paper for determining pH of an aqueous solution. We have to know that the color of litmus paper is blue (or) red.

Complete answer:
According to the given question, we are provided with three test tubes A, B, and C. Test tube A has distilled water, test tube B has an acidic solution, and test tube C has a basic solution.
So, let us now perform the litmus test in the solutions. We have to perform the litmus test by placing a drop of each solution on a small bit of litmus paper (or) we have to dip the litmus paper in each of the solutions to determine if the solutions are basic, acidic (or) neutral.
We saw that test tube A is distilled water. So, when we dip the litmus paper in test tube A, we will not notice any change in the color of litmus paper.
We saw that test tube B is an acidic solution. So, when we dip the litmus paper in test tube B, we will notice a change in color of the litmus paper. The color of the litmus paper will be from blue to red.
We saw that test tube C is the basic solution. So, we have to take the red litmus paper which we got from solution present in test tube C. When we dip the litmus paper in test tube C, we will notice a change in color of the litmus paper. The color of the litmus paper will be from red to blue.
We can now test again distilled water present in test tube A with red litmus paper. So when we dip the litmus paper in test tube A, we will not notice any change in the color of litmus paper.
Thus, we can conclude the type of solution from following observations:
Distilled water that is found in test tube A is neutral because in that solution, we did not observe any change in color.
In test tube B, we have identified the solution as acidic because we observe a change in color from blue litmus paper to red litmus paper.
In test tube C, we have identified the solution as basic because we observe a change in color from red litmus paper to blue litmus paper.

Note:
We have to know while performing the litmus test; we should not dip the entire litmus paper into the entire solution; this is because the dye found in the litmus paper would contaminate the entire solution. In a neutral solution, the color of litmus paper would be changed to purple.