CBSE Class 10 Science 2019 · Paper 31/5/3 · Question 5(b)
A student prepared solutions of
- (i)an acid and
- (ii)a base in two separate beakers but forgot to label the solutions and litmus paper is not available in the laboratory. Since both the solutions are colourless, how will he distinguish between the two using (a) phenolphthalein and (b) methyl orange ?
Answer
Phenolphthalein turns pink in the base and stays colourless in the acid; methyl orange turns red in the acid and yellow in the base.
(a) Add a few drops of phenolphthalein to a sample of each solution: the base turns pink, while the acid remains colourless.
(b) Add a few drops of methyl orange to a fresh sample of each solution: the acid turns red, while the base turns yellow.
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