OCR A level Chemistry Questions and Answers

OCR A level Chemistry Questions and Answers Electronegativity The tendancy of an atom to attract the bonding pair of electrons in a covalent bond Radical A molecule, atom or ion with an unpaired electron Acid (bronsted lowry theory) A molecule or atom that can donate a proton Base A molecule or atom which can act as a proton acceptor Alkali A water soluble base Standard Conditions 298 K, 100 kPa, 1 moldm^-3 Standard enthalpy change of a reaction (delta H r) The enthalpy change when equation quantities of reactants react under standard conditions and in standard states. Standard enthalpy change of formation (delta H f) The enthalpy change when one mole of a compound is formed from its elements under standard conditions and in standard states. Standard enthalpy change of combustion (delta H c) The enthalpy change when one mole of a compound is burned completely in oxygen under standard conditions and in standard states. Heterolytic fission A bond breaks and both bonding electrons go to one atom/molecule. Two ions are formed. Homolytic fission A bond breks and each atom gainn s an electron. This produces 2 radicals. Polyamides (nylons) A polymer linked by amide groups, usually made by reacting a diamine with a dicarboxylic acid. Isomers Molecules with the same molecular formula, but a different arrangement of atoms in space. Stereo isomers Molecules that have the same molecular formula and order of atoms, but a different spatial arrangement. Structural isomers Molecules with the same molecular formula but the atoms are arranged in a different order. Chiral carbon This is a carbon atom attached to 4 different groups, meaning there is no symmetry. Enantiomers This is a molecule which shows optical isomerism. This means that they have a chiral carbon so can form two non super-imposable mirror image molecules. They bend plane polarised light differently. Aliphatic An aliphatic compound does not contain a benzene ring. Aromatic An aromatic compound does contain a benzene ring. Alicyclic A compound with a cyclic hydrocarbon but that doesn't contain benzene. Complex ion Ions with a central metal ion bonded to one or more molecules or ions. Homogenous catalyst A catalyst in the same state as the reactants. Heterogenous catalyst A catalyst in a different state to the reactants. Catalyst poison Molecules which adsorb more strongly to the catalyst than the reactants, while being unable to broken down by the catalyst. This makes the catalyst inactive since its surface is blocked by the poison. Catalyst A species that speeds up a reaction without being used up by creating an alternate pathway for the reaction to take place which lowers the activation enthalpy. Chemisorption Adsorbtion through a chemical means (the 3d and 4s electrons from transition metals can be used to form weak bonds) Sacrificial metal A metal which reacts in preference to another (e.g. zinc becomes corroded before the iron) Carbon carbon double bond In a C=C bond there is one sigma bond, from the overlap of the s orbitals, and one pi bond, which consists of two negatively charged areas above and below. Heating under reflux Boiling the reactant mixture while condensing the vapours back into the flask. Overall reaction for when halide radicals react with ozone O + O3 - O2 +O2 Polar bonds When atoms on either side of the bond attract electrons unequally, causing a dipole. Ether R-O-R