Question

In organic chemistry, which of the following elements is estimated by difference?
A) Nitrogen.
B) Oxygen.
C) Hydrogen.
D) Sulfur.

Answer 1

We know that the Lassaigne test is the qualitative analysis that is done for the identification of nitrogen, halogen, and sulfur in an organic compound. It is also called a sodium fusion test. In a chemical reaction, we can predict the number of molecules or elements by quantitative analysis method.

Complete step by step answer:
Now we can discuss the lassaigne test principle :
The principle behind the sodium fusion test is the modification of the presented element into its ionic form by the sodium metal.
We can write the equation to get nitrogen ion by sodium is, $Na + C + N \to NaCN$
The formation of ionic form of sulfur by sodium is, $2Na + S \to N{a_2}S$
The formation of ionic form of halogen by sodium is, $Na + X \to NaX$
The presence of nitrogen is confirmed by the Lassaigne's test in which ferric ferrocyanide is formed as a blue coloured solution.in this test ferrous sulphate is added to sodium fusion extract and boiled with concentrated sulphuric acid.
Prussian blue color complex ferric ferrocyanide confirms the presence of nitrogen.

So, the correct answer is Option A.

Note: Now we see the procedure to carry out the Lassaigne test:
Gently heat the small piece of sodium metal in a fusion tube and melt the metal till it forms a shining globule.
Here we need to add our sample and heat continuously till the bottom of the tube becomes red then break the hot tube in a china dish.
Boil the contents then cool and filter. The filtrate is known as Lassaigne’s extract.
We can separate this solution to carry the detection of other elements.