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 ${Fe}^{3+}$ ions whose yellow colour makes the blue colour of ferric ferrocyanide to appear green

Answer 1

The correct option is D Of excess of ${Fe}^{3+}$ ions whose yellow colour makes the blue colour of ferric ferrocyanide to appear green

Usually, the colour observed in Lassaigne's test for nitrogen is blue due to presence of ferric ferrocyanide.
However, when excess of ${Fe}^{3+}$ ions are present, the colour may change to green.
${Fe}^{3+}$ ions have yellow colour. When blue colour is mixed with yellow colour, green shade is obtained.