Question

While doing qualitative analysis in chemistry lab, Abhishek added yellow coloured potassium chromate solution into a test tube. He was surprised to see the colour of the solution changing immediately to orange. He realised that the test tube was not clean and contained a few drops of some liquid. Which of the following substances will be the most likely liquid to be present in the test tube before adding potassium chromate solution?

• A. Sodium hydrogen carbonate solution
• B. Methyl orange solution
• C. Sodium hydroxide solution
• D. HCl solution

Hint:

Acidic solutions like HCl convert yellow potassium chromate to orange potassium dichromate. This is a simple redox reaction in an acidic medium.

Answer 1

The Correct Option is D

Potassium chromate (K2CrO4) is yellow in colour, and when it reacts with an acid, such as HCl, it changes to orange-coloured potassium dichromate (K2Cr2O7). This is due to the acidic medium, which facilitates the conversion of chromate to dichromate. The presence of HCl in the test tube before the addition of potassium chromate causes this colour change.