WJEC Chemistry for A2: Study and Rev Guide

Knowledge and Understanding U3 Physical and Inorganic Chemistry This unit builds on ideas studied in both units in year 1 of the course. Many topics within this unit rely on a firm understanding and recall of year 1 ideas and you may find it useful to review the year 1 topic before starting your study of the year 2 content. This unit examines how the behaviour of matter can be studied and described mathematically. This allows us to predict which reactions are feasible and the stability of substances using ideas of enthalpy and entropy. We can predict how far reactions will progress using ideas of equilibria and how fast they will occur using the ideas of rates. Electrochemistry allows us to study the properties of redox reactions and explain the behaviour of batteries and fuel cells. Inorganic chemistry classifies the behaviour of a wide range of elements, with all compounds except those based on hydrocarbons being in this category. The behaviour of elements of the p -block are exemplified by the compounds and reactions of elements in groups 3, 4 and 7. The behaviour of elements of the d -block are exemplified by the compounds and reactions of elements in the first row of the transition elements. Re v i s ed i t ! 3.1 Redox and standard electrode potential Redox reactions can be undertaken in electrochemical cells which separate reduction and oxidation reactions. This allows the oxidising power of each half-cell to be measured using the standard electrode potential by comparison with the standard hydrogen electrode. Any cell can be represented by a cell diagram and its EMF can be measured and used to assess the feasibility of reaction. Fuel cells use electrochemical principles to release the energy very efficiently. p8–12 3.2 Redox reactions Redox reactions can be used in titrations. These allow the concentrations of a wide range of substances to be assessed. The titration for Cu 2+ ions is undertaken in two steps with the Cu 2+ used to produce iodine which is then analysed in a titration with thiosulfate. p13–15 3.3 Chemistry of the p -block The arrangement of electrons in the p -block elements governs their patterns of behaviour. The oxidation states of these elements are affected by the inert pair effect and octet expansion, as well as the trends to metallic behaviour down the group. Group 3 elements formmany electron deficient species, as well as analogues for the allotropes of carbon. Group 4 elements show very different behaviour due to the significant variation in the inert pair effect and metallic properties down the group. Group 7 elements and compounds show trends in reactions based on the stability of their oxidation states. p16–23 Basic notes Good grasp Fully revised A2 Chemistry: Study and Revision Guide 6