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Samples A, B, C and D are tested for their nature using turmeric and Phenolphthalein and the following observations are recorded. A- turns reddish-brown on adding turmeric B- turns pink on adding Phenolphthalein C- turns yellow on adding turmeric D- remains colourless on adding Phenolphthalein What can be concluded about the nature of A, B, C and D?

Samples A, B, C and D are tested for their nature using turmeric and Phenolphthalein and the following observations are recorded. A- turns reddish-brown on adding turmeric B- turns pink on adding Phenolphthalein C- turns yellow on adding turmeric D- remains colourless on adding Phenolphthalein What can be concluded about the nature of A, B, C and D? Correct Answer A, B are bases and C, D are acids

The correct answer is A, B are bases and C, D are acids.

Explanation:

  • There are many natural materials that indicate the presence of acid or base in a solution, such as red cabbage leaves, turmeric, and coloured petals of various flowers. These are known as acid-base indicators or simply indicators.
  • Turmeric is a yellow-coloured chemical that occurs naturally.
  • Turmeric compound, which is an acid-base indicator, remains yellow when acid or neutral solutions are added to it.
    • Acid turns yellow on adding turmeric.
    • Base turns reddish-brown on adding turmeric.
  • To test for acids and bases, synthetic indicators such as methyl orange and phenolphthalein are used.
  • When the solution is basic, phenolphthalein gives a pink colour. 
    • Base turns pink on adding Phenolphthalein.
  • When the solution is acidic, it remains colourless.
    • Acid remains colourless on adding Phenolphthalein.

​​Thus, A, B are bases and C, D are acids.

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