Hydrogen is the most abundant element in the universe. On earth, however, it is rarely found in the free state because of its high reactivity, and usually occurs in combined forms such as water and hydrocarbons. Owing to its unique properties, hydrogen has a wide range of applications. It is used in cutting and welding metals, as a reducing agent for extracting metals from their oxides, in the preparation of vanaspati ghee from vegetable oils and in the manufacture of many important chemicals. Today, hydrogen is widely regarded as a potential clean fuel of the future.

(a) Why is hydrogen known as a clean fuel ?

(b) Define the process used to prepare vanaspati ghee from vegetable oils. Name a catalyst used in this process.

(c) Why is hydrogen used for cutting and welding metals ?

(d) Why is hydrogen not used in weather forecasting balloons anymore ?

(e) Name the gas which has replaced hydrogen in these balloons. Why ?

(a) Hydrogen is called a clean fuel because on burning it produces only water. It does not produce smoke, carbon dioxide, or harmful gases, so it does not pollute the environment.

(b) The process used to prepare vanaspati ghee from vegetable oils is called catalytic hydrogenation. In this process, hydrogen gas is passed through vegetable oil in the presence of a catalyst such as nickel to convert it into vanaspati ghee.

(c) Hydrogen is used for cutting and welding metals because it burns in oxygen to produce an oxy-hydrogen flame of very high temperature. This high heat is useful for cutting and welding metals.

(d) Hydrogen is not used in weather forecasting balloons anymore because it is highly inflammable and can catch fire easily. It may cause explosions, making it unsafe.

(e) Helium has replaced hydrogen in these balloons because it is non-flammable and lighter than air, so it can lift balloons safely.