Question

Identify the gas from the following observations:

A colourless and odourless gas, which is neutral towards litmus. It explodes with a ‘pop’ sound when a burning wooden splint is held near it.

Answer 1

The gas which burns with a ‘pop’ sound is Hydrogen gas (H₂).

In practical Chemistry, two types of analysis are done.

1. Qualitative analysis: The analysis which aims at detecting the presence of any substance in a given sample.
2. Quantitative analysis: The analysis which aims at knowing the quantity of any substance present in a sample.

In qualitative analysis, following types of tests are done:

• Preliminary tests are the initial tests that give us an idea of a substance. These tests include observations like the color, smell and physical state of any substance. These tests give us a hint of what an unknown substance might be.
• Confirmatory tests are the tests that follow a preliminary test. These tests include the chemical reactions that help us to confirm that chemical substance.

This pop sound serves as a confirmatory test for the presence of Hydrogen as a gas.

Evolution of Hydrogen gas:

Zinc (Zn) displaces Hydrogen (H) from Sulphuric acid (H₂SO₄) to produce hydrogen gas.

$$\begin{gathered} \mathrm{Zn}\left(\mathrm{s}\right)+{\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)\to {\mathrm{ZnSO}}_4\left(\mathrm{aq}\right)+{\mathrm{H}}_2\left(\mathrm{g}\right) \\ \left(\mathrm{Zinc}\right)(\mathrm{Sulphuric}\mathrm{acid})(\mathrm{Zinc}\mathrm{sulphate})\left(\mathrm{Hydrogen}\right) \end{gathered}$$

When a burning matchstick is brought near the mouth of the test tube containing hydrogen gas, it produces a pop sound.

Further, Hydrogen is neutral i.e.; neither acidic nor basic in nature due to which it does not change the colour of the litmus paper.