You are given three test tubes. The three test tubes contain distilled water, an acidic solution and the basic solution, respectively. There is only red litmus paper available in order to identify what is there in each test tube. How will you find out what is in each of the test tubes?

Solution: We can identify the content in each of the test tubes using red litmus paper. This can be done by noticing the colour change of the red litmus paper.

• On litmus paper, the three solutions in the test tubes are poured separately.
• The solution which turns red litmus to blue contains a basic solution.
• Divide the formed blue litmus paper into two parts.
• The solution from the test tube, which turns blue litmus paper to red, will be the acidic solution.
• The solution of the test tube, which does not change either red or blue litmus paper, contains water.

NOTE: After immediate distillation, distilled water has a pH of 7. However, within a few hours after distillation, it absorbs carbon dioxide from the atmosphere and turns slightly acidic with a pH of 5.8.