Question

A stain of curry on a white cloth becomes reddish brown. when soap is scrubbed on it. It turns yellow again when the cloth is washed with plenty of water. It had turned reddish brown because:
1. Soap is basic nature
2. Soap is acidic in nature
3. Soap is neutral
4. None of the above
5.

Answer 1

Correct Answer - Option 1 : Soap is basic nature

The correct answer  Soap is basic nature

• A stain of curry on white cloth becomes reddish-brown when soap is rubbed because curry contains turmeric which is a natural indicator whereas soap is basic in nature. Hence, option 1 is correct.
• When turmeric reacts with soap it turns reddish-brown.
• A pH value is greater than 7 is basic in nature. Examples are  Ca(OH)2, NaOH, NaHCO3.
• The yellow stain of curry turns reddish-brown when soap is scrubbed on it because of the fact that soap solution is basic in nature which changes the colour of turmeric in the curry stain to red-brown.
  • This stain turns yellow again when the cloth is rinsed with water because then the basic soap gets removed with water.
• Soap is a combination of a weak acid (fatty acids) and a strong base (lye), which results in what is known as “alkali salt,” or a salt that is basic on the pH scale. Hence, options 2 & 3 are incorrect.