GCSE to A-level progression

Transcription

1 . GCSE to A-level progression AQA A-level Chemistry is a natural next stage from the GCSE course and so there are many recognisable topics that are taken a stage further. Some topics, such as atomic structure, are studied in greater detail while others, such as equilibria, broaden the GCSE experience and then use mathematics so that the qualitative understanding becomes more quantitative. The biggest content difference at A-level is the great increase in the amount of organic chemistry. This includes many more functional groups, an understanding of the mechanisms of the reactions as well as beginning an understanding of synthetic routes. In many cases a single GCSE topic links to more than one A-level topic. In this document they have been presented together to illustrate the overlap and expansion at A-level. Atomic structure GCSE specification ref: C1.1.1, C2.3.1 A-level specification ref: 1.1 The understanding of fundamental particles in the nucleus is extended to include using the relative abundance of isotopes to calculate the relative atomic mass. Mass spectrometry (Time of Flight) is considered. The understanding of electronic arrangement is modified to include consideration of levels and sub-levels (orbitals) as details within the GCSE model. This is extended to include the atoms and ions up to Z = 36. Ionisation energy trends in Period 3 and in Group 2 are used as evidence for this model. Jan 2013 CH2HP Q7b A-level question: Jan 2013 Chem1 Q1 Amount of substance GCSE specification ref: C2.3.3, C3.4.1 A-level specification ref: 1.2 The familiar concepts of relative atomic mass, relative molecular mass, empirical formulas and percentage yield are revisited and extended to include the Avogadro constant, the mole concept and the ideal gas equation. Balanced equations are used to calculate concentrations and volumes in acid-base reactions, masses, gas volumes, percentage yield and percentage atom economy. Jan 2013 CH1HP Q1 A-level question: Jan 2013 Chem1 Q5 Bonding GCSE specification ref: C2.1, C2.2

2 A-level specification ref: 1.3 The three familiar bonding types (ionic, covalent and metallic) are the starting point. Dative covalency is considered as well as electronegativity and the polarity of covalent bonds. The four kinds of crystal structure (ionic, metallic, macromolecular and molecular) are studied again in general with some specific examples studied too. The melting point and conductivity of a substance is linked to its structure along with the energy changes associated with the changes of state. Intermolecular forces are considered in more detail than at GCSE. A new topic is understanding how the shape of a molecule is determined in terms of the repulsion of its bonding pairs and lone pairs of electrons. Jan 2013 CH2HP Q5c, Q6, Q7a A-level question: Jan 2013 Chem1 Q3 (a,b,c) Energetics, Thermodynamics GCSE specification ref: C2.5, C3.3 A-level specification ref: 1.4 (Energetics) 1.8 (Thermodynamics) Exothermic and endothermic reactions, calorimetry and bond enthalpies are familiar from GCSE and then developed. Hess s Law is used with enthalpy of formation and enthalpy of combustion to calculate enthalpy changes for reactions. This concept is extended to a wide range of enthalpy changes to create and use Born-Haber cycles. The concept of entropy is introduced and then the balance between enthalpy change and entropy change is linked to the feasibility of a reaction using the concept of free-energy change. Jan 2013 CHY3H Q1 A-level question: Jan 2013 Chem2 Q4, Jan 2013 Chem5 Q1,2,3 Kinetics, Rate equations GCSE specification ref: C2.4 A-level specification ref: 1.5 (Kinetics) 1.9 (Rate equations) The familiar concepts of collision theory and activation energy provide the starting place and the changes in rate of reaction due to concentration, pressure, temperature and catalysts are linked to them. A qualitative understanding of the Maxwell-Boltzmann distribution helps to explain these changes more fully. Rate equations give some further quantitative rigour and the order of reaction with respect to a reactant is used to provide information about possible mechanisms. Jan 2013 CH2HP Q1 A-level question: Jan 2013 Chem4 Q1 Chemical equilibria and Le Chatelier's principle, Equilibrium constant Kc for homogeneous systems

3 GCSE specification ref: C3.5 A-level specification ref: 1.6 (Chemical equilibria...) 1.10 (Equilibrium constant...) The dynamic nature of equilibrium and the qualitative effects of changes of pressure, temperature and concentration on an equilibrium are known from GCSE in terms of the Haber process. At A-level, these same ideas are linked to Le Chatelier s principle and applied to other industrial processes. The concept of Kc, the equilibrium constant, is introduced in a later topic and is the basis for calculations. A-level question: Jan 2013 Chem2 Q2, Jan 2013 Chem4 Q3 Oxidation, reduction and redox equations, Electrode potential and electrochemical cells GCSE specification ref: C1.3.1, C1.4, C2.7, C3.3, C3.6 A-level specification ref: 1.7 (Oxidation..) 1.11 (Electrode potential..) At GCSE the concept of redox is spread over many areas. At A-level, the concept of electron loss and gain is developed and the idea of combining half-equations to make full balanced equations is introduced. Although at GCSE, electrochemistry was seen from the electrolysis point of view, the main thrust of electrochemistry at A-level is to consider cells both as a theoretical way of determining the feasibility of a reaction and as a commercial source of electrical energy. Simple cells, rechargeable cells and fuel cells are all considered. Jan 2013 CH2HP Q5c A-level question: Jan 2013 Chem5 Q7 Acids and bases GCSE specification ref: C2.6, C 3.4 (limited) A-level specification ref: 1.12 The GCSE model of acids and bases is vastly extended to involve an understanding of the concept of ph in terms of the concentration of hydrogen ions rather than the effect on ph paper. There is a detailed mathematical approach to determine the ph of acids and alkalis of various concentrations and also how the ph changes during a titration. The action and use of buffer solutions are studied. The titration calculations are extended to cover more complicated combinations of acids and bases (eg diprotic acids reacting with sodium hydroxide). Jan 2013 CH2HP Q3 A-level question: Jan 2013 Chem4 Q2 Periodicity, Properties of Period 3 elements and their oxides

4 GCSE specification ref: C1.1(limited) C2.1(limited), C2.2 (limited), C3.1 A-level specification ref: 2.1 (Periodicity) 2.4 (Properties of Period 3 Elements..) At GCSE, trends in the periodic table are mostly up and down within groups. There is some understanding of the periodic change in the number of electrons in the outside shell of the atoms. The comparison of structures leads, indirectly, to some limited understanding of periodicity. At A-level, the trends in physical properties across Period 3 is used as part of the evidence for the model of the atom. These trends are also linked to the structure and bonding within the elements. This is extended to a study of the trends of the chemical properties of the elements and their oxides across Period 3. A-level question: Jan 2013 Chem1 Q2, Jan 2013 Chem5 Q4, Jan 2013 Chem5 Q1,2,3 Group 2, the alkaline Earth Metals GCSE specification ref: C1.2 (limited), C3.1, C3.4 A-level specification ref: 2.2 At GCSE, limestone is studied which involves some Group 2 chemistry linked to the uses. The GCSE trends in the periodic table are mostly up and down within groups and although Group 1 is considered at GCSE, the same sort of argument, in more detail, is used for the trend in Group 2 at A-level. The relative solubilities of hydroxides and sulfates are linked to their uses. A-level question: Jan 2013 Chem2 Q1c Group 7 (17), the halogens GCSE specification ref: C3.1, C3.2, C3.4 A-level specification ref: 2.3 At GCSE, the trends in reactivity of the halogens is studied and at A-level this is extended to view this as oxidising power of the halogens and reducing power of the halide ions. The analysis of halides using silver nitrate solution is extended to include the use of ammonia solution. The use of chlorine in water treatment is also an extension from GCSE. A-level question: Jan 2013 Chem2 Q9, Q10 Transition metals GCSE specification ref: C3.1 A-level specification ref: 2.5

5 Although metals is studied in terms of structure and bonding, the GCSE course only touches on the recall that transition metals have different properties to Group 1 metals and that transition metals can form ions with different charges, form coloured compounds and can act as catalysts. At A-level, the atomic-level reason why these properties occur and the three typical reactions of transition metals (ligand substitution, redox and hydrolysis) are studied in much more detail so that the facts are understood rather than simply known. Jan 2013 CH1HP Q7 A-level question: Jan 2013 Chem5 Q5, Q6 Reactions of ions in aqueous solution GCSE specification ref: C3.4 A-level specification ref: 2.6 The analysis section of GCSE has various ions forming precipitates of various colours when reacting with sodium hydroxide solution and sometimes redissolving on addition of excess. This kaleidoscope of factual recall is organised in terms of the charge of the ions and their polarising effect on the coordinated water molecules. This leads to a rational understanding to replace the list of facts. A-level question: Jan 2013 Chem5 Q8 Introduction to organic chemistry, Optical isomerism GCSE specification ref: C1.4, C1.5, C3.6 A-level specification ref: 3.1 (Introduction to organic chemistry) 3.7 (Optical isomerism) Terms like structural formula, isomer were introduced in GCSE but limited to very simple substances. This expands at A-level to include many forms of isomerism. Similarly, although the difference between alkane and alkene was understood and there was a limited understanding of alcohols, carboxylic acids and esters, A-level brings an understanding of nomenclature applicable to a much wider range of functional groups. Jan 2013 CH1HP Q3 A-level question: Jan 2013 Chem4 Q4 Alkanes GCSE specification ref: C1.4 A-level specification ref: 3.2 The formation and fractional distillation of crude oil to yield alkanes, the burning of these as fuels and their conversion, by cracking, into alkenes and smaller, more useful alkanes is

6 covered in some detail at GCSE. This is revisited at A-level and taken to a little more depth by studying the cracking processes more carefully and by considering the role of catalytic converters in the reduction of pollution. Jan 2013 CH1HP Q3 A-level question: Jan 2013 Chem1 Q4 Halogenoalkanes GCSE specification ref: A-level specification ref: 3.3 The study of halogenoalkanes at A-level provides a starting point for the idea of a synthetic pathway. Alkanes can be converted into halogenoalkanes which can then form alcohols, amines, alkenes and nitriles, each of which can lead on to other functional groups. The problem of chlorofluorocarbons in the atmosphere is also considered. This is also a starting point for the study of the mechanisms by which reactions proceed. Rather than treating the reaction simply as a recipe, students are encouraged to understand why and how the reaction proceeds. A-level question: Jan 2013 Chem2 Q7, Q8 Alkenes GCSE specification ref: C1.5 A-level specification ref: 3.4 GCSE views alkenes as a useful product from the cracking of alkanes. This leads on to polymers. A-level extends this to use the alkenes as a stepping stone to other functional groups. The theoretical understanding of the mechanism of electrophilic addition is developed as well as a consideration of some industrial processes. CH2HP Q4 A-level question: Jan 2013 Chem2 Q8 Alcohols GCSE specification ref: C1.5, C3.6 A-level specification ref: 3.5 Fermentation and oil-based routes are compared at GCSE along with some very simple chemistry of alcohols. A-level looks at this comparison in more detail including an understanding of the term 'biofuel'. Oxidation of alcohols by acidified potassium dichromate is used as a means of distinguishing the different categories of alcohol.

7 CH1HP Q6 A-level question: Jan 2013 Chem2 Q5 Organic analysis, Nuclear magnetic resonance spectroscopy, Chromatography GCSE specification ref: C2.3 A-level specification ref: 3.6 (Organic analysis) 3.15 (Nuclear magnetic resonance spectroscopy) 3.16 (Chromatography) Chemical analysis to identify functional groups contributes to the identification of many of the functional groups studied. Gas chromatography and mass spectrometry are introduced briefly at GCSE. These, as well as infra-red spectroscopy and nuclear magnetic resonance spectroscopy (both 1H and 13C), are used individually and together to provide information for structure determination. Some theoretical background to how these techniques is studied as well as interpretation of results. Mass spectrometry now uses the Time of Flight technique. A-level question: Jan 2013 Chem4 Q5 Aldehydes and ketones, Carboxylic acids and derivatives GCSE specification ref: C3.6 A-level specification ref: 3.8 (Aldehydes and ketones) 3.9 (Carboxylic acids and derivatives) GCSE just touches on carboxylic acids and esters. At A-level, aldehydes and ketones are considered as the oxidation products of alcohols and as functional groups in their own right. Nucleophilic addition and reduction add to the compendium of mechanisms and the further oxidation to carboxylic acids. The reaction of carboxylic acids with alcohols to form esters widens the range of synthetic pathways. Acylation by acyl chlorides and acid anhydrides are compared, especially in the context of usefulness in an industrial setting. Formation of biodiesel, soap manufacture and aspirin production are all studied. A-level question: Jun 2012 Chem4 Q4 Aromatic chemistry GCSE specification ref: A-level specification ref: 3.10 This topic is not studied at GCSE. It is part of the huge expansion of organic chemistry from GCSE to A-level. Aromatic substances behave in a different way to aliphatic ones as a result of the unusual electron arrangement in the benzene ring. The reasons for this difference are explored and the reactions of benzene are studied along with their mechanism.

8 A-level question: Jun 2012 Chem4 Q6 Amines GCSE specification ref: A-level specification ref: 3.11 This topic is not studied at GCSE. It is part of the huge expansion of organic chemistry from GCSE to A-level. Amines are studied in terms of their being a derivative of ammonia. Hence, their basic and nucleophilic properties are considered. A-level question: Jun 2012 Chem4 Q10b Polymers GCSE specification ref: C1.5.2 A-level specification ref: 3.12 GCSE looks at half of the story, dealing with addition polymers as products from alkene-like substances. At both levels the chemical aspects of the polymerisation as well as the environmental issues are studied but at A-level the field is widened to cover condensation polymers (polyesters such as Terylene and polyamides such as Kevlar) as well. Seeing both kinds of polymer allows comparison of the biodegradability and disposal of the two types. A-level question: Jan 2013 Chem4 Q4 Amino Acids, Proteins and DNA GCSE specification ref: C1.7.2 A-level specification ref: 3.13 GCSE touches on this topic in terms of the history of the atmosphere and a possible explanation for the start of life on Earth. A-level studies amino acids as substances having two functional groups. Proteins are formed as amino acids join together and that some of these proteins are biological catalysts called enzymes. The interaction between enzymes and substrates and between drugs and enzymes is studied. The structure of DNA as the sum of its component parts, the role of hydrogen bonding in the structure leading to the double helix and the action of the anti-cancer drug cisplatin to disrupt the replication brings A-level chemistry close to biology and biochemistry. Jan 2013 CH1HP Q8 A-level question: Jan 2013 Chem4 Q4

9 Organic synthesis GCSE specification ref: C1.5, C3.6 A-level specification ref: 3.14 The limited range of functional groups studied at GCSE limits the possibilities to create synthetic pathways. This also limits the opportunities for analysis. On the other hand, A-level has a wide range of functional groups so some ingenuity is required to create not only a multi-step synthetic pathway that works but also to take issues such as good yield into consideration. Jan 2013 CH1HP Q6 A-level question: Jan 2013 Chem4 Q6