CHEMISTRY

• Hydrocarbons are compounds containing the elements carbon and hydrogen only
• A homologous series is a group of compounds that:

  • can be represented by the same general formula;
  • have similar chemical properties;
  • patterns are often seen in the physical properties of the members of a homologous series.
• increasing strength of the intermolecular forces as the molecular size increases.
• The molecular formula only shows the number of atoms of each element in one molecule of the substance
• The full structural formula shows all the atoms and all the bonds within the molecule and shows exactly which is joined to which
• The shortened structural formula shows how the atoms are joined but only shows some, if any, of the bonds
• The structure of any molecule can be represented by either molecular formula, full structural formula or a shortened structural formula.
• • Alkanes:
  • are a homologous series of saturated hydrocarbons;
  • are commonly used as fuels;
  • are insoluble in water;
  • can be represented by the general formula CnH2n+2
• • Cycloalkanes:
  • are a homologous series of saturated, cyclic hydrocarbons;
  • are used as fuels and solvents;
  • are insoluble in water;
  • can be represented by the general formula CnH2n
• • Alkenes:
  • are a homologous series of unsaturated hydrocarbons;
  • are used to make polymers and alcohols;
  • contain the C=C double bond;
  • can be represented by the general formula CnH2n
• • Isomers:
  • are compounds with the same molecular formula but different structural formulae;
  • may belong to different homologous series;
  • usually have different physical properties.
• Compounds containing carbon to carbon double bonds can take part in addition reactions. In an addition reaction, two molecules combine to form a single molecule.
• • It is possible to distinguish an unsaturated compound from a saturated compound using bromine solution.
  • Unsaturated compounds quickly decolourise bromine solution.
• • The solubility, boiling point and volatility (ease of evaporation) of a compound can be predicted by considering:
  • the presence of O-H or N-H bonds, which implies hydrogen bonding;
  • the arrangement of polar covalent bonds which could result in a molecule possessing a permanent dipole;
  • molecular size which would affect London dispersion forces;
  • the polarities of solute and solvent.
• • Polar or ionic compounds tend to be soluble in polar solvents, non-polar compounds tend to be soluble in non-polar solvents.
• • Solubility, boiling point and volatility can be explained in terms of the type and strength of intermolecular forces present.
• What name is given to the part of a molecule which gives the compound its characteristic properties?

  functional group
• Which of the following is the characteristic reaction of an alkene?

  addition
• Which of the following types of compound could not be obtained by an addition reaction involving an alkene?

  alkanal
• Ethanol can be prepared in industry by an addition reaction between steam and ethene.

  Give another name for this type of reaction.

  hydration
• Much of the flavour of food depends on our sense of smell.

  In order to excite this sense, molecules must:

  be volatile
• When considering the boiling point of molecules, which of the following properties are important?

  type of intermolecular bonding and molecular mass
• In general, volatile molecules are:

  •  small with weak bonds between molecules.
• In order to retain the oil-soluble flavour of a vegetable, it should be cooked for a:

  short time in boiling water
• • An alcohol is a molecule containing a hydroxyl functional group, -OH group.
• Alcohols can be classified as primary, secondary or tertiary
• • Alcohols containing two hydroxyl groups are called diols, and those containing three hydroxyl groups are called triols.
• • Hydroxyl groups make alcohols polar and this gives rise to hydrogen bonding.
• • Hydrogen bonding can be used to explain the properties of alcohols, including boiling points, melting points, viscosity and solubility/miscibility in water.
• • A carboxylic acid is a molecule containing the carboxyl functional group, -COOH.
• • Carboxylic acids can react with bases:
  • metal oxide + carboxylic acid → salt + water
  • metal hydroxide + carboxylic acid → salt + water
  • metal carbonate + carboxylic acid → salt + water + carbon dioxide
• Which two of the following describe possible uses of carboxylic acids?

  In the manufacture of vinegar.

  In the production of polyester fibres
• • An ester is a molecule containing an ester link -COO-.
• Esters can be named given the:

  • names of their parent alcohol and carboxylic acid;
• • Esters are used as flavourings and fragrances as many have pleasant, fruity smells, and they are also used as solvents for non-polar compounds that do not dissolve in water.
• Esters are formed by a condensation reaction between an alcohol and a carboxylic acid - in a condensation reaction, two molecules are joined together with the elimination of a small molecule
• • When an ester link is formed by the reaction between a hydroxyl group and a carboxyl group, the small molecule eliminated is water.
• • Esters can be hydrolysed to produce an alcohol and a carboxylic acid - in a hydrolysis reaction, a molecule reacts with water to break down into smaller molecules.
• Apart from perfumes, name one other use for esters.

  solvents
• Name the ester formed when butanoic acid reacts with methanol.

  methyl butanoate