Carbon Compounds
Carbon Compounds
This domain tests the unique bonding of carbon, hydrocarbons, homologous series, functional groups, isomerism and the chemistry of ethanol and ethanoic acid.
Core rules
- Carbon is tetravalent and forms four covalent bonds; catenation lets carbon atoms link into chains, branches and rings.
- Saturated hydrocarbons contain only single C–C bonds (alkanes); unsaturated ones contain double (alkenes) or triple (alkynes) bonds.
- A homologous series has the same general formula and functional group, with successive members differing by CH₂ and about 14 u in molar mass.
- Functional groups determine chemical properties: –OH alcohol, –COOH carboxylic acid, –CHO aldehyde, –CO– ketone, –NH₂ amine.
- Isomers have the same molecular formula but different structures, e.g. n-butane and isobutane, C₄H₁₀.
- Alkenes and alkynes undergo addition; alkanes undergo substitution. Ethanol is oxidised to ethanoic acid.
- Ethanoic acid is a weak acid; ethanol burns and is used as a solvent and fuel.
Worked example
Ethanol has formula C₂H₅OH. Its molar mass = (2×12) + (6×1) + 16 = 46 g/mol. On oxidation it forms ethanoic acid, CH₃COOH, whose molar mass is (2×12) + (4×1) + (2×16) = 60 g/mol. The change adds one oxygen atom and removes two hydrogen atoms overall, so the product is a carboxylic acid with the –COOH group.
Traps
Do not confuse molecular formula with structural formula. All alkenes are not isomers of alkanes. Ethanoic acid is not a strong mineral acid. In a homologous series, physical properties change gradually but the functional group stays the same.