Question

Sometimes, the colour observed in Lassaigne’s test for nitrogen is green. It is because:

• A. of green colour of ferrous sulphate
• B. ferric ferrocyanide is also green
• C. of green colour of copper sulphate
• D. of excess of Fe³+ ions whose yellow colour makes the blue colour of ferric ferrocyanide appear green

Hint:

Colour changes in qualitative tests often arise due to colour mixing.

Answer 1

The Correct Option is D

Step 1: Positive nitrogen test gives Prussian blue colour (ferric ferrocyanide).
Step 2: Excess Fe³+ ions impart yellow colour.
Step 3: Yellow + blue appears green.