CBSE Class 10 Science 2017 · Paper 531/3 · Question 7

Hydrogenation is the addition of hydrogen to an unsaturated carbon compound (one with a double or triple bond between carbon atoms) in the presence of a catalyst; hydrogen adds across the multiple bond and the compound becomes saturated (or less unsaturated). It is an addition reaction. Example: ${\text{CH}}_2={\text{CH}}_2+{\text{H}}_2\stackrel{\text{Ni}}{\to }{\text{CH}}_3-{\text{CH}}_3$ (ethene to ethane). The same reaction converts vegetable oils, which generally have long unsaturated carbon chains, into vegetable ghee (vanaspati). Essential conditions: an unsaturated compound, hydrogen gas and a catalyst such as nickel or palladium; for vegetable oils, hydrogen is passed through the heated oil containing finely divided nickel. Change in physical property: the vegetable oil is a liquid at room temperature, whereas the product, vanaspati ghee, is a solid (semi-solid) at room temperature; the melting point rises.