Cambridge O Level Chemistry · Syllabus 5070 · Organic Chemistry
Hydrocarbon
What is Hydrocarbon?
A compound that contains the elements carbon and hydrogen only; alkanes and alkenes are hydrocarbons, whereas alcohols and carboxylic acids are not, because they also contain oxygen.
This definition is part of the Organic Chemistry chapter in Cambridge O Level Chemistry.
Hydrocarbon in context
A homologous series is a family of organic compounds that share the same functional group and the same general formula, whose successive members differ by a -CH2- unit and show a gradual trend in physical properties with similar chemical properties. Alkanes (CnH2n+2) are saturated hydrocarbons with only single bonds and limited reactivity; alkenes (CnH2n) are unsaturated, containing a reactive C=C double bond; alcohols (CnH2n+1OH) contain -OH; and carboxylic acids (CnH2n+1COOH) contain -COOH and behave as acids. Substitution replaces one atom and displaces another; addition opens a double bond to form a single product; condensation polymerisation releases a small molecule at each linkage, while addition polymerisation releases nothing.
Common mistakes with Hydrocarbon
- “Petroleum is a compound that is broken down in the fractionating column.” why it fails Two errors at once: petroleum is not a compound, and distillation does not break anything down. correct Petroleum is a mixture of hydrocarbons. Fractional distillation separates that mixture using differences in boiling point. No bonds inside the molecules are broken. Taught in 11.3.
- “Kerosene boils at 180 °C.” why it fails A fraction is itself a mixture of hydrocarbons of similar chain length, so it does not have one fixed boiling point, and the syllabus supplies no numbers. correct Fractions condense over a range of boiling points. Answer in terms of higher and lower, not in invented degrees. Taught in 11.3.