Three test tubes contain water, citric acid solution and sodium hydroxide solution. How do you recognize them?

Using an indicator such as litmus. In a solution of citric acid (acidic medium) litmus will have a red color, in a solution of caustic soda (alkaline medium) – blue, and in water (neutral medium) – violet. It is impossible to recognize acid with phenolphthalein indicator.

Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.