Carbon and Its Compounds
The paper tests tetravalency and catenation, allotropes, saturated and unsaturated hydrocarbons, functional groups, homologous series, isomerism, and the chemistry of ethanol and ethanoic acid.
Why carbon is special
Carbon is tetravalent and shows catenation, forming long chains, branches and rings. Its allotropes - diamond, graphite and fullerene - differ only in the arrangement of atoms. Diamond is hard and does not conduct; graphite is soft, layered and conducts.
Families and functional groups
- Alkanes are saturated (CnH2n+2); alkenes have a double bond (CnH2n); alkynes have a triple bond (CnH2n−2).
- Functional groups: alcohol –OH, aldehyde –CHO, ketone –CO–, carboxylic acid –COOH, halide –X.
- A homologous series differs by one CH2 unit and 14 u in mass, with members sharing a general formula and similar chemistry.
- Isomers have the same molecular formula but different structures.
Two named reactions
Ethanol and ethanoic acid with a little concentrated H2SO4 as catalyst give ethyl ethanoate and water - esterification; esters have fruity smells. Boiling oils or fats with NaOH gives soap and glycerol - saponification. A soap molecule has a hydrocarbon tail that dissolves in grease and an ionic head that dissolves in water, so micelles lift dirt away. Hard water forms scum with soap.
Worked example
Name CH3–CH2–CH2–OH and predict its reaction with ethanoic acid. There are three carbons with an –OH on the first carbon, so the name is propan-1-ol. With ethanoic acid it forms propyl ethanoate and water, because the –OH of the alcohol and the –COOH of the acid combine into the ester link –COO–.
Traps
Coal and petroleum are mixtures, not compounds; graphite conducts although it is non-metallic; ethanol is oxidised to ethanoic acid; do not confuse saponification with esterification.