Before battery-powered lamps became available in the early 1900s, carbide lamps that made use of a chemical reaction to produce a flammable hydrocarbon gas that burned with a bright, sooty flame were commonly used on bicycles and motor cars - Leaving Cert Chemistry - Question 1 - 2021

Gas B is acetylene (C2H2).

When liquid A (water) is added to calcium carbide, a vigorous reaction occurs, producing gas B (acetylene) and calcium hydroxide. The reaction is exothermic and may produce bubbles and heat.

The method of collection indicates that gas B (acetylene) is not soluble in water, as it is collected over water.

The first few test-tubes of gas produced are not used because they may contain air or other impurities from the reaction, thus yielding inaccurate results.

The term 'unsaturated' refers to a hydrocarbon that contains at least one double or triple bond, indicating that it can react further and add hydrogen or other atoms.

To test for unsaturation, you can add a few drops of bromine water to the sample. If the reddish-brown color of bromine disappears, it indicates the presence of a double bond, confirming that the sample is unsaturated.

When gas B (acetylene) is burned in pure oxygen, the flame is:

1. Bright and luminous, producing a white light suitable for welding.
2. Very hot, reaching temperatures high enough to melt metals.