Advanced Higher Chemistry Student Learning Outcomes CHEMISTRY DEPARTMENT ADVANCED HIGHER GRADE CHEMISTRY LEARNING OUTCOMES UNIT 1 Electronic Structure and the Periodic Table 2 Principles of Chemical Reactions 3 Organic Chemistry 533571242 Page 1 of 31 Advanced Higher Chemistry Student Learning Outcomes UNIT 1 Electronic Structure and the Periodic Table (a) Electronic Structure (i) Electromagnetic Spectrum and Associated Calculations (ii) Electronic Configuration and the Periodic Table (iii) Spectroscopy (b) Chemical Bonding (i) Covalent Bonding (ii) Shapes of Molecules and Polyatomic Ions (iii) Ionic Lattices, Superconductors and Semiconductors (c) Some Chemistry of the Periodic Table 2 (i) The Second and Third Short Periods: Oxides, Chlorides and Hydrides (ii) Electronic Configuration and Oxidation States of Transition Metals (iii) Transition Metal Complexes Principles of Chemical Reactions (a) Stoichiometry (b) Chemical Equilibrium (i) Reactions at Equilibrium (ii) Equilibria Between Different Phases (iii) Equilibria Involving Ions (c) Thermochemistry (i) Hess’s Law (ii) Bond Enthalpies (iii) Hess’s Law Applied to Ionic Substances (d) Reaction Feasibilty (i) Entropy (ii) Free Energy (e) Electrochemistry (f) 533571242 Kinetics Page 2 of 31 Advanced Higher Chemistry Student Learning Outcomes UNIT 3 Organic Chemistry (a) Permeating Aspects of Organic Chemistry (i) Reaction Types (ii) Reaction Mechanisms (iii) Physical Properties (b) Systematic Organic Chemistry (i) Hydrocarbons and Halogenoalkanes (ii) Alcohols and Ethers (iii) Aldehydes, Ketones and Carboxylic Acids (iv) Amines (v) Aromatics (c) Stereoisomerism (i) Geometric Isomerism (ii) Optical Isomerism (d) Structural Analysis (i) Elemental Microanalysis and Mass Spectrometry (ii) Infra – red and Nuclear Magnetic Resonance Spectrometry and X – ray Crystallography (e) Medicines 533571242 (i) Historical Development (ii) How a Medicine Functions Page 3 of 31 Advanced Higher Chemistry Student Learning Outcomes ADVANCED HIGHER CHEMISTRY STUDENT LEARNING OUTCOMES UNIT 1 - ELECTRONIC STRUCTURE AND THE PERIODIC TABLE (a) ELECTRONIC STRUCTURE ( i) Electromagnetic Spectrum and Associated Calculations LEARNING OUTCOME SCHOLAR LTS NOTES CHEM in CONTEXT 1. Electromagnetic radiation may be described in terms of waves. 2 1 2. Electromagnetic radiation can be specified by its wavelength () and by its frequency (). 2 1 3. The electromagnetic spectrum is the range of frequencies or wavelengths of electromagnetic radiation. 2 3 4. The unit of measurement of wavelength is the metre or an appropriate sub-multiple. 3 1 5. The unit of measurement of frequency is the reciprocal of time in seconds (s -1) and is called the Hertz (Hz). 3 1 6. The velocity of electromagnetic radiation is constant and has a value of approximately 3 x 108 ms-1. 2 1 7. Velocity, frequency and wavelength are related in the expression: c = . 3 2 8. Under certain circumstances electromagnetic radiation may be regarded as a stream of particles, rather than as waves. These particles are known as photons. 12 4 9. The energy (E) of radiation, and the energy associated with photons, is related to frequency by Planck’s constant (h) in the expressions: E = h for one photon E = Lh for one mole of photons where L is Avogadro’s Constant. 12 – 13 4 65 SCHOLAR LTS NOTES CHEM in CONTEXT ( ii) Electronic Configuration and the Periodic Table LEARNING OUTCOME 1. The emission spectrum of hydrogen provides evidence of energy levels. 19 5–6 65 2. Quantum theory states that matter can only emit or absorb energy in small fixed amounts (called quanta). 19 4 65 3. The energy of a bound electron in an atom is quantised. 19 6 4. An atom can be considered as emitting a photon of light energy when an electron moves from a higher energy level to a lower energy level. 20 6 5. Each line of the emission spectrum represents radiation of a specific wavelength or frequency from which the difference in energy between the levels can be calculated. 20 7 6. Emission spectra of elements with more than one electron provide evidence of sublevels within each principal energy level above the first. 21 10 7. The principal energy levels correspond to the principal shells. The second and subsequent principal shells contain sub-shells that correspond to the sub-levels. 22 10 533571242 Page 4 of 31 70 Advanced Higher Chemistry ( ii) Student Learning Outcomes Electronic Configuration and the Periodic Table SCHOLAR LTS NOTES CHEM in CONTEXT 22 12 71 Heisenberg’s uncertainty principle states that it is impossible to define with absolute precision, simultaneously, both the position and the momentum of an electron. 23 11 10. Electrons, like photons, display the properties of particles and waves. 23 11 11. Treating bound electrons in atoms as waves leads to regions of high probability of finding the electrons. These regions are called atomic orbitals. 23 11 72 12. There are four types of orbitals, namely s, p, d and f, each with a characteristic shape or set of shapes. Diagrams of the shapes of s and p orbitals can be drawn and recognised. Diagrams of d orbitals can be recognised. 23 – 25 12 – 13 72 13. An orbital holds a maximum of two electrons, as required by the Pauli exclusion principle. 28 14 72 14. The number of orbitals in each sub-shell is as follows: 23 – 25 13 71 - 72 LEARNING OUTCOME 8. 9. Sub-shells can be labelled s, p, d and f. The types of sub-shells within each principal shell are as follows: Principal shell Sub-shell(s) present 1 s 2 s and p 3 s, p and d 4 s, p, d, and f Sub-shell Number of orbitals s one s orbital p three p orbitals d five d orbitals f seven f orbitals 15. In an isolated atom the orbitals within each sub-shell are degenerate. 24 12 16. The Aufbau principle states that orbitals are filled in order of increasing energy. 28 16 17. The relative energies corresponding to each orbital can be represented diagrammatically for the first four shells of a multi-electron atom. 29 16 – 17 18. Hund’s Rule states that when degenerate orbitals are available, electrons fill each singly, keeping their spins parallel before spin pairing starts. 28 17 19. Electronic configurations using spectroscopic notation and orbital box notation can be written for elements of atomic numbers 1 to 36. 28 – 30 16 20. The Periodic Table can be subdivided into four blocks (s, p, d and f) corresponding to the outer electronic configurations of the elements within these blocks. 30 – 31 18 21. The variation in first ionisation energy with increasing atomic number for the first 36 elements can be explained in terms of the relative stability of different electron configurations, and so provides evidence for these electronic configurations. 31 – 32 18 – 19 22. The relative values of first, second and subsequent ionisation energies can be explained in terms of the stabilities of the electronic configurations from which the electrons are being removed. 33 – 34 20 ( iii) Spectroscopy 533571242 Page 5 of 31 71 70 Advanced Higher Chemistry Student Learning Outcomes SCHOLAR LTS NOTES CHEM in CONTEXT Atomic emission spectroscopy and atomic absorption spectroscopy involve transitions between electronic energy levels in atoms. Generally, the energy differences correspond to the visible region of the electromagnetic spectrum, i.e., to the approximate wavelength range of 400-700 nm. Some applications use the ultra-violet region (wavelength range approximately 200-400 nm). 6–7 20 – 21 64 – 65 2. In emission spectroscopy the sample is energised by heat or electricity causing electrons to be promoted to higher energy levels. The wavelength of the radiation emitted as electrons fall back to lower energy levels is measured. 6–7 21 64 – 65 3. In absorption spectroscopy electromagnetic radiation is directed at the sample. Radiation is absorbed as electrons are promoted to higher energy levels. The wavelength of the absorbed radiation is measured. 6–7 21 4. Each element provides a characteristic spectrum which can be used to identify an element. 6–7 21 5. The amount of species can be determined quantitatively if the intensity of emitted or transmitted radiation is measured. 7–8 21 – 22 (b) CHEMICAL BONDING ( i) Covalent Bonding SCHOLAR LTS NOTES CHEM in CONTEXT 39 – 40 23 97 LEARNING OUTCOME 1. LEARNING OUTCOME 1. Non- polar covalent bonding and ionic bonding can be considered as being at opposite ends of a bonding continuum with polar covalent bonding lying between these two extremes 65 2. Different electron models can be used to explain the experimental evidence associated with covalent bonding. 38 23 – 26 91 3. Lewis electron dot diagrams represent bonding and non-bonding electron pairs in molecules and in polyatomic ions. 41 26 87 4. A dative covalent bond is one in which one atom of the bond provides both electrons of the bonding pair. 42 27 88 5. Species such as ozone, sulphur dioxide and the carbonate ion can be represented by equivalent electron dot diagrams known as resonance structures 42 – 43 27 – 28 93 – 94 533571242 Page 6 of 31 Advanced Higher Chemistry ( ii) Student Learning Outcomes Shapes of Molecules and Polyatomic ions LEARNING OUTCOME 1. The shapes of molecules or polyatomic ions can be predicted from the number of bonding electron pairs and the number of non-bonding electron pairs. 2. The arrangement of electron pairs is linear, trigonal, tetrahedral, trigonal bipyramidal and octahedral when the total number of electron pairs is 2, 3, 4, 5 and 6, respectively. 3. Electron pair repulsions decrease in strength in the order: non- bonding pair/ non-bonding pair > non-bonding pair/ bonding pair > bonding pair/ bonding pair. 4. These different strengths of electron pair repulsion account for slight deviations from expected bond angles in molecules such as NH3 and H2O. ( iii) Ionic Lattices, Superconductors and Semiconductors SCHOLAR LTS NOTES CHEM in CONTEXT 44 29 92 45 – 46 29 –- 33 92 44 – 45 29 92 44 30 – 31 92 SCHOLAR LTS NOTES CHEM in CONTEXT 50 34 – 35 125 – 126 50 34 – 35 124 – 126 SCHOLAR LTS NOTES CHEM in CONTEXT Io n ic L a t t ic e s LEARNING OUTCOME 1. 2. ( iii) The geometry of the crystalline structure adopted by an ionic compound depends on the relative sizes of the ions. This affects the number of ions which can pack round an ion of opposite charge. Examples of crystal lattice structures are: sodium chloride; caesium chloride. Ionic Lattices, Superconductors and Semiconductors Superconductors LEARNING OUTCOME 1. Superconductors are a special class of materials that have zero electrical resistance at temperatures near absolute zero 51 36 2. Achieving temperatures near absolute zero is difficult and costly so application of superconduction at these temperatures is impractical 51 36 3. Recently superconductors have been discovered which have zero resistance up to temperatures above the boiling point of liquid nitrogen-temperatures, which are less costly to attain 51 36 4. Superconductors may have future applications in power transmission and electrically powered forms of transport. 52 37 – 38 533571242 Page 7 of 31 Advanced Higher Chemistry ( iii) Student Learning Outcomes Ionic Lattices, Superconductors and Semiconductors Semiconductors SCHOLAR LTS NOTES A covalent element such as silicon or germanium which has a higher conductivity than that of a typical non-metal but a much lower conductivity than that of a metal is described as a semiconductor 53 38 + 40 2. Semiconductors are also referred to as metalloids and occur at the division between metals and non-metals in the Periodic Table 53 40 3. The electrical conductivity of semiconductors increases with increasing temperature 53 38 4. The electrical conductivity of semiconductors increases on exposure to light. This is known as the photovoltaic effect. 53 40 5. Elements such as silicon and germanium have similar structures to diamond but the covalent bonds are weaker. Thermal agitation of the lattice can result in some of the bonding electrons breaking free, leaving positive sites called ‘holes’. 53 40 6. When a voltage is applied to these elements, electrons and holes can migrate through the lattice. 53 40 7. Doping pure crystals of silicon or germanium with certain other elements produces n-type and p-type semiconductors. 54 41 – 42 8. The type of semiconduction depends on the specific dopant used. 54 42 9 In n-type and p-type semiconductors the main current carriers are surplus electrons and positive holes respectively. 54 42 10 Crystals of silicon or germanium can be prepared with bands of n-type or p-type semiconductors. The p-n junction which occurs between a layer of n-type and a layer of p-type semiconductor has specific electrical properties which form the basis of the electronics industry. 54 42 Solar cells use the photovoltaic effect to convert sunlight into electricity. 54 43 LEARNING OUTCOME 1. 11 533571242 Page 8 of 31 CHEM in CONTEXT Advanced Higher Chemistry Student Learning Outcomes (c) SOME CHEMISTRY OF THE PERIODIC TABLE ( i) The Second and Third Short Periods: Oxides, Chlorides and Hydrides LEARNING OUTCOME SCHOLAR LTS NOTES CHEM in CONTEXT 1. Melting points, boiling points and electrical conductivities of the oxides, chlorides and hydrides of the elements of the second and third periods can be explained in terms of their structure and type of bonding. 60 – 73 44 – 53 177 – 182 2. Metal oxides tend to be basic and non-metal oxides tend to be acidic but amphoteric oxides exhibit both acidic and basic properties. 63 – 64 44 – 45 181 – 182 3. Most ionic chlorides dissolve in water without reaction but some covalent chlorides are hydrolysed, producing fumes of hydrogen chloride. 66 48 179 4. Ionic hydrides possess the hydride ion, H─, which acts as a reducing agent. 69 51 5. In reaction between water and ionic hydrides the products are hydrogen gas and the hydroxide ion. 69 51 6. Electrolysis of molten ionic hydrides produces hydrogen gas at the positive electrode. 68 51 ( ii) Electronic Configuration and Oxidation States of Transition Metals SCHOLAR LTS NOTES CHEM in CONTEXT Electronic Configuration LEARNING OUTCOME 1. The d block transition metals are metals with an incomplete d sub-shell in at least one of their ions. 77 54 251 2. The filling of the d-orbitals follows the Aufbau principle, with the exception of chromium and copper atoms. These exceptions are due to a special stability associated with all the d-orbitals being half filled or completely filled. 78 54 – 55 250 3. When transition metals form ions it is the s electrons which are lost first rather than the d electrons. 79 55 251 ( ii) Electronic Configuration and Oxidation States of Transition Metals SCHOLAR LTS NOTES CHEM in CONTEXT Oxidation States LEARNING OUTCOME 1. An element is said to be in a particular oxidation state when it has a specific oxidation number. 80 55 29 2. The oxidation number is determined by following certain rules 81 55 – 56 29 – 30 3. Transition metals exhibit variable oxidation states of differing stability. 82 – 86 57 254 4. Compounds of the same transition metal but in different oxidation states may have different colours. 90 57 255 5. Oxidation can be considered as an increase in oxidation number and reduction can be considered as a decrease in oxidation number. 87 56 31 6. Compounds containing metals in high oxidation states tend to be oxidising agents whereas compounds with metals in low oxidation states are often reducing agents. 89 57 533571242 Page 9 of 31 Advanced Higher Chemistry ( iii) Student Learning Outcomes Transition Metal Complexes LEARNING OUTCOME SCHOLAR LTS NOTES CHEM in CONTEXT 1. A complex consists of a central metal ion surrounded by ligands 91 59 202 2. Ligands are electron donors and may be negative ions or molecules with non-bonding pairs of electrons. Ligands can be classified as monodentate, bidentate, etc. 91 59 202 3. The number of bonds from the ligand to the central metal ion is known as the co-ordination number of the central ion. 92 60 257 4. Complexes are written and named according to I.U.P.A.C. rules. 93 60 – 61 202 5. In a complex of a transition metal the d orbitals are no longer degenerate. 100 62 260 6. The energy difference between subsets of d orbitals depends on the position of the ligand in the spectrochemical series. 105 63 203 7. Colours of many transition metal complexes can be explained in terms of d-d transitions. 99 – 100 62 – 64 259 – 260 PPA PPA 1: Preparation of Potassium Trioxalatoferrate(III). ( iii) Transition Metal Complexes SCHOLAR LTS NOTES CHEM in CONTEXT 100 64 384 100 – 101 65 385 100 65 101 65 385 SCHOLAR LTS NOTES CHEM in CONTEXT U.V. And Visible Spectroscopy LEARNING OUTCOME 1. The effects of d-d transitions can be studied using ultra-violet and visible absorption spectroscopy. 2. Ultra-violet and visible absorption spectroscopy involve transitions between electronic energy levels in atoms and molecules where the energy difference corresponds to the ultra- violet and visible regions of the electromagnetic spectrum. 3. PPA The wavelength ranges are approximately 200-400 nm for ultra-violet and 400-700 nm for visible. An ultra-violet / visible spectrometer measures the intensity of radiation transmitted through the sample and compares this with the intensity of incident radiation. PPA 2: Colorimetric Determination of Manganese in Steel. ( iii) Transition Metal Complexes 4. Catalysis LEARNING OUTCOME 1. Transition metals or their compounds act as catalysts in many chemical reactions 105 66 261 2. It is believed that the presence of unpaired d electrons or unfilled d-orbitals allows intermediate complexes to form, providing reaction pathways of lower energy compared to the uncatalysed reaction 106 67 262 3. The variability of oxidation states of transition metals is also an important factor. 106 68 533571242 Page 10 of 31 Advanced Higher Chemistry Student Learning Outcomes ADVANCED HIGHER CHEMISTRY STUDENT LEARNING OUTCOMES UNIT 2 – PRINCIPLES OF CHEMICAL REACTIONS (a) STOICHIOMETRY Stoichiometry LEARNING OUTCOME SCHOLAR LTS NOTES CHEM in CONTEXT 15 – 16 1. A quantitative reaction is one in which the substances react completely according to the mole ratios given by the balanced (stoichiometric) equation. 3–9 1 2. Volumetric analysis involves using a solution of accurately known concentration in a quantitative reaction to determine the concentration of another substance. 9 1 3. A solution of accurately known concentration is known as a standard solution. A standard solution can be prepared directly from a primary standard. 10 2 9 2 10 – 13 3 11 4. A primary standard must have, at least, the following characteristics: high state of purity; very stable; high solubility; reasonably high formula mass. 5. The volume of reactant solution required to just complete the reaction is determined by titration. 6. The equivalence point is the point at which the reaction is just complete. The ‘end point’ is the point at which a change is observed and is associated with the equivalence point. An indicator is a substance which changes colour at the endpoint. 10 2 331 7. Acid / base titrations are based on neutralisation reactions 9 3 11 - 12 8. Complexometric titrations are based on complex formation reactions. 14 3 11 – 13 4 15 – 16 7-8 E.D.T.A. is an important complexometric reagent and can be used to determine the concentration of metal ions such as nickel(II). PPA PPA 1: The Complexometric Determination of Nickel using EDTA. 9. Redox titrations are based on redox reactions. Substances such as potassium manganate(VII) which can act as their own indicators are very useful reactants in redox titrations In gravimetric analysis the mass of an element or compound present in a substance is determined by chemically changing that substance into some other substance of known chemical composition, which can be readily isolated, purified and weighed. PPA 2: The Gravimetric Determination of Water in Hydrated Barium Chloride. 10. PPA 533571242 Page 11 of 31 207 – 208 Advanced Higher Chemistry Student Learning Outcomes (b) CHEMICAL EQUILIBRIUM ( i) Reactions at Equilibrium LEARNING OUTCOME SCHOLAR LTS NOTES CHEM in CONTEXT 1. A chemical reaction is in equilibrium when the composition of the reactants and products remains constant indefinitely. 22 9 289 – 290 2. The equilibrium constant (K ) characterises the equilibrium composition of the reaction mixture. 24 10 299 3. The equilibrium constant can be measured in terms of concentrations or, for gaseous reactions, in terms of pressure. For the general reaction: 26 10 300 – 301 24 10 298 4. a A + b B cC+dD [C] c [D] d K= [A] a [B] b where [A], [B], [C] and [D] are the equilibrium concentrations of A, B, C and D, respectively, and a, b , c and d are the stoichiometric coefficients in a balanced reaction equation. 5. In a homogeneous equilibrium all the species are in the same phase. 27 10 303 6. In a heterogeneous equilibrium the species are in more than one phase. The concentrations of pure solids or pure liquids are constant and are given the value 1 in the equilibrium equation. 27 10 303 7. Equilibrium constants are independent of the particular concentrations or pressures of species in a given reaction. 26 10 299 8. Equilibrium constants depend on the reaction temperature. 34 13 299 9. Le Chatelier’s principle states that when a reaction at equilibrium is subject to change the composition alters in such a way as to minimise the effects of that change. 33 13 306 10. For endothermic reactions a rise in temperature causes an increase in K, i.e., the yield of the product is increased. 34 14 308 11. For exothermic reactions a rise in temperature causes a decrease in K, i.e., the yield of the product is decreased. 34 14 308 12. The effects of changes in concentration or pressure on the position of equilibrium can be explained quantitatively in terms of a fixed equilibrium constant. 32 – 33 11 + 15 13. The presence of a catalyst does not affect the equilibrium constant. 35 – 36 14 533571242 Page 12 of 31 308 Advanced Higher Chemistry ( ii) Student Learning Outcomes Equilibria Between Different Phases Partition Coefficient LEARNING OUTCOME SCHOLAR LTS NOTES CHEM in CONTEXT 1. When a solute is shaken in two immiscible liquids it partitions itself between the two liquids in a definite ratio called the partition coefficient. 40 17 294 2. The value of the partition coefficient depends on the immiscible liquids involved, the solute and the temperature. 41 17 295 – 296 PPA PPA 3: Determination of a Partition Coefficient. ( ii) Equilibria Between Different Phases SCHOLAR LTS NOTES CHEM in CONTEXT 42 17 296 43 17 296 SCHOLAR LTS NOTES CHEM in CONTEXT 47 20 47 – 50 20 47 – 48 20 – 22 49 22 – 23 Solvent Extraction LEARNING OUTCOME 1. 2. Solvent extraction is an application of the partition of a solute between two liquids. Applications of solvent extraction include the purification of water-soluble organic acids using a suitable organic solvent. ( ii) Equilibria Between Different Phases Chromatography LEARNING OUTCOME 1. Chromatographic separations depend on the partition equilibrium between two phases, one stationary and the other mobile. 2. There are several types of chromatography. Examples are: paper chromatography; gas-liquid chromatography 3. In paper chromatography, the stationary phase is the water held on the paper and the mobile phase is another solvent. In gas-liquid chromatography the stationary phase is a liquid held on a solid support and the mobile phase is a gas. 4. 533571242 Page 13 of 31 Advanced Higher Chemistry ( iii) Student Learning Outcomes Equilibria Involving Ions Acid / Base Equilibria LEARNING OUTCOME SCHOLAR LTS NOTES CHEM in CONTEXT 1. The Bronsted - Lowry definitions of acid and base state that an acid is a proton donor and a base is a proton acceptor. 54 23 199 2. For every acid there is a conjugate base, formed by loss of a proton. 55 23 199 3. For every base there is a conjugate acid, formed by gain of a proton. The ionisation of water can be represented by: 55 23 199 59 24 199 56 24 470 59 24 326 4. H2O(l) + H2O(l) 5. 6. H3O+(aq) + OH─ (aq) Water is amphoteric. The dissociation constant for the ionisation of water is known as the ionic product and is represented by: Kw = [H3O+][OH─] 7. The value of the ionic product varies with temperature. 60 25 326 8. At 25 oC the value of Kw is approximately 1 x 10-14 mol 2 l –2. 61 25 326 9. A shorthand representation of H3O+ is H+. Stoichiometric equations and 58 25 198 61 25 325 64 26 329 64 26 329 55 26 199 equilibrium expressions can be written using H+ instead of H3O+ where the meaning is clear. 10. 11. 12. 13. 14. 15. 16. The relationship between pH and the hydrogen ion concentration is given by: pH = -log10 [H+] The acid dissociation constant of acid HA is given by: HA(aq) + H2O(l) H3O+ (aq) + A- (aq) The acid dissociation constant of acid HA is given by: [ H3O ][A ] Ka = [HA] The conjugate base of an acid of general formula HA is A─. The dissociation constant of an acid can be represented by pKa where pKa = - logK a The relationship of the pH of a weak acid to its dissociation constant is given by: pHa = ½ pKa - ½ log c The dissociation in aqueous solution of base of general formula B can be represented as: B( aq) + H2O(l) BH+ (aq) + OH─ (aq) 17. The conjugate acid of a base of general formula B is BH+. 18. The dissociation of the conjugate acid of the base can be represented as: BH+ (aq) + H2O(l) 533571242 B(aq) + H3O+ (aq) Page 14 of 31 65 66 27 68 28 66 28 67 28 330 Advanced Higher Chemistry ( iii) Student Learning Outcomes Equilibria Involving Ions Acid / Base Equilibria SCHOLAR LTS NOTES CHEM in CONTEXT 67 28 330 SCHOLAR LTS NOTES CHEM in CONTEXT 72 29 331 72 30 331 In aqueous solution the colour of the acid is distinctly different from that of its conjugate base. 72 30 331 23. The colour of the indicator is determined by the ratio of [HIn ] to [In─]. 72 30 331 24. The theoretical point at which colour changes occurs when [H+]= KIn. 75 30 332 25. 75 30 26. The colour change is assumed to be distinguishable when [HIn] and [In─] - differ by a factor of 10. The pH range over which a colour change occurs can be estimated by the expression: pH = pKIn ±1 75 30 ( iii) Equilibria Involving Ions LEARNING OUTCOME 19. ( iii) The dissociation constant for the conjugate acid is: [B][H 3O ] Ka = [BH ] Equilibria Involving Ions Indicators LEARNING OUTCOME 20. Indicators are weak acids for which the dissociation can be represented as: HIn(aq) + H2O(l) 21. 22. H3O + (aq) + In─ (aq) The acid dissociation constant is represented as K In and is given by the following expression: [H3O ][In ] KIn = [HIn] 533571242 Page 15 of 31 Advanced Higher Chemistry Student Learning Outcomes Buffer Solutions LEARNING OUTCOME SCHOLAR LTS NOTES CHEM in CONTEXT 27. A buffer solution is one in which the pH remains approximately constant when small amounts of acid or base are added. 79 33 334 28. An acid buffer consists of a solution of a weak acid and one of its salts. 79 33 334 29. In an acid buffer solution the weak acid can supply hydrogen ions when these are removed by the addition of a small amount of base. The salt of the weak acid provides the conjugate base, which can absorb excess hydrogen ions produced by the addition of a small amount of acid. 80 33 335 30. A basic buffer consists of a solution of a weak base and one of its salts. 79 33 334 31. In a basic buffer solution the weak base removes excess hydrogen ions and the conjugate acid provided by the salt supplies hydrogen ions when these are removed. 82 33 83 – 84 34 335 84 – 85 35 335 – 336 32. The pH of an acid buffer solution can be calculated from its composition and from the acid dissociation constant. [acid] [H3O+(aq)] = Ka × [salt] or pH = pKa – log 33. [acid] [salt] The required compositions of an acid buffer solution can be calculated from the desired pH and from the acid dissociation constant. 533571242 Page 16 of 31 Advanced Higher Chemistry (c) THERMOCHEMISTRY ( i) Hess’s Law Student Learning Outcomes LEARNING OUTCOME SCHOLAR LTS NOTES CHEM in CONTEXT 1. Thermochemistry concerns the study of changes in energy which occur during chemical reactions. 90 37 146 2. The First Law of Thermodynamics states that energy is conserved. 94 38 147 3. Hess’s law states that the overall reaction enthalpy is the sum of the reaction enthalpies of each step of the reaction. This is an application of the First Law of Thermodynamics. 93 – 94 38 151 4. A thermochemical cycle can be used to calculate an unknown enthalpy value. 94 38 152 – 153 The term ‘standard enthalpy change’ refers to an enthalpy change for a reaction in which the reactants and products are considered to be in their standard states at a specified temperature. 95 37 148 6. The standard state of a substance is the most stable state of the substance under standard conditions. 95 37 7. Standard conditions refer to a pressure of one atmosphere and a specified temperature, usually 298 K (25 °C). 95 37 148 8. The standard molar enthalpy of combustion refers to the enthalpy change which occurs when one mole of a substance is burned completely. 95 37 150 9. Calorimetry is the term used to describe the quantitative determination of the change in heat energy which occurs during a chemical reaction. A calorimeter is used to measure the quantity of heat energy given out or taken in during a chemical reaction. The standard molar enthalpy of formation refers to the enthalpy change which occurs when one mole of a substance is prepared from its elements in their standard states. The standard enthalpy of formation of a substance can be calculated from standard enthalpy changes which are experimentally determined. 98 40 150 99 37 150 95 37 148 95 – 96 38 – 39 151 97 39 153 SCHOLAR LTS NOTES CHEM in CONTEXT For a diatomic molecule, XY, the molar bond enthalpy is the energy required to break one mole of XY bonds, that is, for the process: X─Y(g) X(g) + Y(g) 91 41 2. Mean molar bond enthalpies are average values which are quoted for bonds which occur in different molecular environments. 93 41 3. Bond enthalpies may be calculated from data on enthalpy changes. 92 42 4. The enthalpy of a reaction can be estimated from a thermochemical cycle involving bond formation and bond dissociation Enthalpies of reaction estimated from bond enthalpies may differ from experimentally determined values. 94 42 – 43 158 93 44 159 5. 10. 11. 12. 13. ( ii) (Ho) The standard enthalpy of a reaction can be calculated from tabulated standard molar enthalpies of formation using the relation: Ho = H of (products) - H of (reactants) Bond Enthalpies LEARNING OUTCOME 1. 5. 533571242 Page 17 of 31 158 Advanced Higher Chemistry ( iii) Student Learning Outcomes Hess’s Law Applied to Ionic Substances Born – Haber Cycle SCHOLAR LTS NOTES CHEM in CONTEXT 100 45 – 46 161 101 – 102 45 162 103 45 160 100 46 161 102 – 103 46 161 102 46 149 103 46 85 LEARNING OUTCOME SCHOLAR LTS NOTES CHEM in CONTEXT A thermochemical cycle can represent the relation between enthalpy of solution, enthalpy of lattice formation and enthalpy of hydration for the solution of an ionic compound. 105 – 106 47 – 48 163 105 47 163 LEARNING OUTCOME 1. 2. 3. 4. 5. 6. The Born – Haber cycle is a thermochemical cycle applied to the formation of an ionic crystal. The Born – Haber cycle can be used to calculate the enthalpy of lattice formation, which cannot be determined directly by experiment. The standard molar enthalpy change of lattice formation is the enthalpy change which occurs when one mole of an ionic crystal is formed from the ions in their gaseous states under standard conditions. The cycle is a closed path which includes as steps the different enthalpy changes involved in the formation of an ionic crystal. The different enthalpy changes include enthalpy of atomisation, ionisation energy, bond enthalpy, electron affinity, lattice enthalpy and enthalpy of formation. The standard molar enthalpy of atomisation of an element is the energy required to produce one mole of isolated gaseous atoms from the element in its standard state. e.g. 7. ½ I 2 (s) I(g) The electron affinity is usually defined as the enthalpy change for the process of adding one mole of electrons to one mole of isolated atoms in the gaseous state, ie, for the change represented by: E(g) + e - (iii) E - (g) Hess’s Law Applied to Ionic Substances Enthalpy of Solution 1. 2. The hydration enthalpy is the energy released when one mole of individual gaseous ions becomes hydrated, i.e., the changes represented by: E n+ (g) E n+ (aq) and 533571242 E n- (g) E n- (aq) Page 18 of 31 Advanced Higher Chemistry (d) ( i) Student Learning Outcomes REACTION FEASIBILITY Entropy LEARNING OUTCOME SCHOLAR LTS NOTES CHEM in CONTEXT 114 49 343 115 – 117 49 344 343 1. The entropy (S) of a system is the degree of disorder of the system. The greater the disorder, the greater the entropy. 2. Entropy increases as temperature increases. 3. Changes of state involve changes in entropy. Melting and evaporation are accompanied by increases in entropy. 115 49 – 50 4. One version of the Third Law of Thermodynamics states that the entropy of a perfect crystal at 0 K is zero. 115 50 5. The standard entropy of a substance is the entropy value for the standard state of the substance. The change in standard entropy for a reaction system can be calculated from the standard entropy values for the reactants and products. 117 51 343 117 – 118 51 344 SCHOLAR LTS NOTES CHEM in CONTEXT One version of the Second Law of Thermodynamics states that the total entropy of a reaction system and its surroundings always increases for a spontaneous process. 120 51 341 2. Heat energy released by the reaction system into the surroundings increases the entropy of the surroundings, whereas heat absorbed by the reaction system from the surroundings decreases the entropy of the surroundings. 119 51 344 3. The change in entropy of the surroundings that occurs as a result of a chemical reaction can be calculated from the temperature and from the enthalpy change for the reaction system. 120 51 345 The total entropy change is proportional to the change in free energy (G) of the reaction system. The direction of spontaneous change is in the direction of decreasing free energy. 122 52 346 122 52 346 346 6. ( ii) Free Energy LEARNING OUTCOME 1. 4. 5. The change in standard free energy for a reaction is related to the standard enthalpy and entropy changes by: G o = H o - TS o 6. The standard free energy change of a reaction can be calculated from the standard enthalpy and standard entropy changes for the reaction. 124 52 7. The standard free energy change of a reaction can be calculated from the standard free energies of formation of the reactants and products. 124 53 8. A reaction is feasible under standard conditions if the change in standard free energy between reactants and products is negative. This means that the equilibrium composition favours the products over the reactants. 125 54 – 56 9. Under non-standard conditions any reaction is feasible if G is negative. 123 52 10. At equilibrium G = 0. 128 53 11. A reaction will proceed spontaneously in the forward direction until the composition is reached where G = 0. 127 53 533571242 Page 19 of 31 Advanced Higher Chemistry ( ii) Student Learning Outcomes Free Energy Application of the Concept of Free Energy LEARNING OUTCOME SCHOLAR 12. The feasibility of a chemical reaction under standard conditions can be predicted from the calculated value of the change in standard free energy (G o). 13. The temperature at which the reaction becomes feasible can be calculated for a reaction for which both H o and S o have positive values. PPA PPA 4: Verification of a Thermodynamic Prediction. 14. LTS NOTES CHEM in CONTEXT 56 – 57 131 56 – 57 Ellingham diagrams are plots of variation of free energy change with temperature and can be used to predict the conditions under which a reaction can occur. 131 57 – 61 15. Ellingham diagrams can be used to predict the conditions required to extract a metal from its ores. 131 57 – 61 (e) ELECTROCHEMISTRY LEARNING OUTCOME SCHOLAR LTS NOTES CHEM in CONTEXT 1. A potential difference is set up when a metal is placed in contact with its ions in solution. 138 – 139 63 22 – 23 2. An electrochemical cell is composed of two half cells between which electrical contact is made by an electrolyte, often in the form of a salt bridge. 140 63 22 – 23 3. Cell and cell emf conventions should be employed according to I.U.P.A.C. recommendations. 141 – 144 64 188 148 65 194 141 – 142 66 188 144 64 191 144 – 145 65 191 Electrochemistry For example, a cell reaction between zinc and copper can be represented as: Zn(s) Zn2+ (aq) ║ Cu2+ (aq)Cu(s) The equation for this cell is written as: Zn(s) + Cu2+(aq) Zn2+(aq) + Cu(s) 4. A positive emf is obtained if the reaction takes place in the direction as written. 5. The emf of a cell (E) is the electric potential difference between the electrodes of the cell, i.e., E(right) - E(left) when no current is drawn. 6. Cell emf depends on the concentration, the temperature and the type of cell. 7. Cell emf values are usually considered at standard conditions. 8. Standard conditions for the measurement of electrode potentials refer to a situation in which all pressures are one atmosphere, concentrations of solutions are one mole per litre and in which temperature is specified normally at 298 K (25 °C). 144 65 191 9. The absolute value of the electrode potential of a half cell cannot be determined experimentally. 145 64 190 10. The standard electrode potential of a half cell is the potential measured against the standard hydrogen electrode under standard conditions. 145 – 147 64 190 11. The standard hydrogen electrode potential is given an arbitrary value of 0·00V. 145 64 190 148 66 194 – 195 12. The emf of a cell under standard conditions can be calculated from the tabulated values of standard reduction potentials. 533571242 (Eo) Page 20 of 31 Advanced Higher Chemistry Student Learning Outcomes Electrochemistry LEARNING OUTCOME SCHOLAR LTS NOTES CHEM in CONTEXT 13. The relative strengths of reducing agents and oxidising agents under standard conditions can be estimated from standard reduction potentials. 148 – 150 65 192 – 193 14. For a standard cell operated under conditions of thermodynamic reversibility the standard free energy change for the cell reaction is related to cell emf by the expression: 151 70 349 154 – 155 71 -72 197 – 198 SCHOLAR LTS NOTES CHEM in CONTEXT 160 75 360 165 – 167 77 360 – 361 G o = -nFE o 15. (f) A fuel cell operates like an electrochemical cell, the only difference being that the fuel for the reaction is provided from external reserves of gas, e.g., the hydrogen / oxygen fuel cell. KINETICS Kinetics LEARNING OUTCOME 1. 2. The rate of a chemical reaction normally depends on the concentrations of the reactants. For a first order reaction the rate of reaction is proportional to the concentration of one reactant and the rate can be expressed as: rate = k [A] where k is the rate constant and [A] is the concentration of reactant A in mol l -1 . 3. The order of a reaction with respect to any one reactant is the power to which the concentration of that reactant is raised in the rate equation. 165 – 167 77 361 4. The overall order of a reaction is the sum of the powers to which the concentrations of the reactants are raised in the rate equation. 165 – 167 77 363 5. In general for a reaction of type: 165 – 167 77 363 166 – 167 78 362 170 80 373 171 – 172 80 374 172 80 – 81 nA + mB product where the rate equation is of the form: rate = k [A ]n[B]m the order of reaction is n with respect to A and m with respect to B and the overall order is n + m. 6. The rate constant can be determined from initial rate data for a series of reactions in which the initial concentrations of reactants are varied. 7. Reaction mechanisms usually occur by a series of steps. 8. The rate of reaction is dependent on the slowest step which is called the ‘rate determining step’. Experimentally determined rate equations can provide evidence for a proposed reaction mechanism but cannot provide proof, as other possible reaction mechanisms may also give the same rate equation. PPA 5: Kinetics of the Acid - Catalysed Propanone / Iodine Reaction. 9. PPA ADVANCED HIGHER CHEMISTRY STUDENT LEARNING OUTCOMES 533571242 Page 21 of 31 Advanced Higher Chemistry Student Learning Outcomes UNIT 3 – ORGANIC CHEMISTRY (a) PERMEATING ASPECTS OF ORGANIC CHEMISTRY ( i) Reaction Types LEARNING OUTCOME 1. ( ii) Equations can be written for the following reaction types and, given equations, these reaction types can be identified as: substitution; addition; elimination; condensation; hydrolysis; oxidation; reduction. ( iii) CHEM in CONTEXT 5 3 See index SCHOLAR LTS NOTES CHEM in CONTEXT 15 – 17 10 – 11 407 – 408 The following reaction mechanisms can be described in terms of electron shifts: (i) radical substitution of alkanes; (ii) electrophilic addition to alkenes carbocation mechanism cyclic ion intermediate mechanism 23 – 26 15 – 19 421 (iii) nucleophilic substitution SN1 and SN2 32 – 33 25 – 28 456 – 459 SCHOLAR LTS NOTES CHEM in CONTEXT 44 32 – 33 103 Physical Properties LEARNING OUTCOME 1. LTS NOTES Reaction Mechanisms LEARNING OUTCOME 1. SCHOLAR The following physical properties are explained in terms of the intermolecular forces involved: melting and boiling points; miscibility with water. 533571242 Page 22 of 31 Advanced Higher Chemistry Student Learning Outcomes (b) SYSTEMATIC ORGANIC CHEMISTRY ( i) Hydrocarbons and Halogenoalkanes LEARNING OUTCOME SCHOLAR LTS NOTES 12 – 13 8 CHEM in CONTEXT 1. Bonding in alkanes can be described in terms of sp3 hybridisation and sigma bonds. 2. Hybridisation is the process of mixing atomic orbitals in an atom to generate a set of new atomic orbitals called hybrid orbitals. 13 8 3. A sigma bond is a covalent bond formed by end-on overlap of two atomic orbitals lying along the axis of the bond. 13 10 419 4. Alkanes undergo substitution reactions with chlorine and bromine by a chain reaction mechanism. The chain reaction includes the following steps: 15 10 – 11 407 – 408 15 – 16 10 – 11 407 – 408 19 – 20 13-14 419 20 14 419 20 – 22 14 – 15 473 23 – 27 15 – 21 422 – 425 23 – 27 17,19 + 21 424 453 5. (i) initiation by homolytic fission to produce radicals; (ii) propagation; (iii) termination. 6. Bonding in ethene can be described in terms of sp2 hybridisation, sigma and pi () bonds. 7. A pi () bond is a covalent bond formed by the sideways overlap of two parallel atomic orbitals lying perpendicular to the axis of the bond. 8. Alkenes can be prepared in the laboratory by: (i) dehydration of alcohols using aluminium oxide, concentrated sulphuric acid or orthophosphoric acid; (ii) base-induced elimination of hydrogen halides from monohalogenoalkanes. PPA PPA 1: Preparation of Cyclohexene. 9. Alkenes undergo: 10. (i) catalytic addition with hydrogen to form alkanes; (ii) addition with halogens to form dihalogenoalkanes; (iii) addition with hydrogen halides according to Markovnikov’s rule to form monohalogenoalkanes; (iv) acid-catalysed addition with water according to Markovnikov’s rule to form alcohols. The mechanisms of the above reactions involve: (i) for halogenation cyclic ion intermediate (ii) for hydrohalogenation carbocation intermediate (iii) for acid catalysed hydration carbocation intermediate 11. Halogenoalkanes are named according to I.U.P.A.C. rules. 28 23 12. Monohalogenoalkanes can be classified as primary, secondary or tertiary. 29 24 – 25 13. Monohalogenoalkanes undergo nucleophilic substitution reactions. React monohalogenoalkanes with alkali and test for halide ion using aqueous ethanolic silver nitrate solution. 32 – 34 25 – 26 533571242 Page 23 of 31 456 Advanced Higher Chemistry ( i) Student Learning Outcomes Hydrocarbons and Halogenoalkanes LEARNING OUTCOME 14. Monohalogenoalkanes undergo elimination reactions to form alkenes. 15. Monohalogenoalkanes react with: ( ii) (i) alkalis to form alcohols; (ii) alcoholic alkoxides to form ethers; (iii) ethanolic cyanide to form nitriles which can be hydrolysed to carboxylic acids (chain length increased by one carbon atom); (iv) ammonia to form amines via alkyl ammonium salts. LTS NOTES CHEM in CONTEXT 30 – 31 30 – 31 462 34 – 36 28 – 29 460 – 462 SCHOLAR LTS NOTES CHEM in CONTEXT 44 – 45 32 – 33 468 47 33 469 48 – 49 34 456, 424 – 425 50 – 51 34 424 – 425 Alcohols and Ethers LEARNING OUTCOME 1. Alcohols exhibit hydrogen bonding and as a result have higher boiling points than other organic compounds of comparable relative formula mass and shape. 2. The lower alcohols are miscible with water but as their chain length increases their solubility in water decreases. Alcohols can be prepared from: (i) alkenes by hydration; 3. SCHOLAR (ii) halogenoalkanes by substitution. 4. In industry, alcohols (except methanol) can be manufactured by the acid-catalysed hydration of alkenes. 5. Alcohols react with some reactive metals to form alkoxides. 51 29 + 34 471 6. Alcohols can be dehydrated to alkenes. 52 35 473 – 474 7. Alcohols undergo condensation reactions slowly with carboxylic acids and more vigorously with acid chlorides to form esters. 53 36 472 8. Ethers have the general formula R'-O-R ''where R 'and R ''are alkyl groups. 43 37 478 9. Ethers are named according to I.U.P.A.C. rules. 43 37 10. Due to the lack of hydrogen bonding, ethers have lower boiling points than the corresponding isomeric alcohols. 46 37 11. Ether molecules can hydrogen-bond with water molecules thus explaining the solubility in water of some ethers of low relative formula mass. 47 38 12. Ethers are highly flammable and on exposure to air may form explosive peroxides. 55 38 478 13. Ethers can be prepared by the reaction of halogenoalkanes with alkoxides. Ethers are used as solvents since they are relatively inert chemically and will dissolve many organic compounds. 54 29 461 55 38 478 14. 533571242 Page 24 of 31 478 Advanced Higher Chemistry ( iii) Student Learning Outcomes Aldehydes, Ketones and Carboxylic Acids LEARNING OUTCOME 1. LTS NOTES CHEM in CONTEXT 60 – 62 41 – 42 483 – 484 65 – 66 42 489 67 43 486 68 – 70 43 484 – 485, 487 69 46 487 The following physical properties of aldehydes and ketones can be explained in terms of dipole-dipole attractions and / or hydrogen bonding: (i) higher boiling points than corresponding alkanes; (ii) lower boiling points than corresponding alcohols; (iii) miscibility of lower members with water. 2. Tollens’ reagent or Fehling’s solution can be used to distinguish between aldehydes and ketones. Aldehydes reduce the complexed silver(I) ion and the complexed copper(II) ion to silver and copper(I) oxide, respectively. 3. Aldehydes and ketones can be reduced to primary and secondary alcohols, respectively, by reaction with lithium aluminium hydride in ether. Aldehydes and ketones undergo: 4. SCHOLAR (i) (ii) nucleophilic addition with HCN to form cyanohydrins which can be hydrolysed to hydroxy carboxylic acids. nucleophilic addition-elimination with hydrazine, 2, 4-dinitrophenylhydrazine to form hydrazones and 2,4-dinitrophenylhydrazones respectively. 5. These nucleophilic addition-elimination reactions are also described as condensation since water is formed in the process. PPA PPA 2: Identification by Derivative Formation. 6. The melting points of the resulting 2, 4-dinitrophenylhydrazones are used to identify unknown aldehydes and ketones. 71 46 – 47 487 7. Aldehydes are generally more reactive than ketones because the presence of two alkyl groups in ketones hinders nucleophilic attack and reduces the partial positive charge on the carbonyl carbon atom. 71 42 484 8. In pure carboxylic acids hydrogen bonding produces dimers thus explaining the relatively high boiling points. Dimerisation does not occur in aqueous solution. 63 48 499 9. Carboxylic acid molecules also form hydrogen bonds with water molecules thus explaining the appreciable solubility of the lower carboxylic acids in water. As the chain length increases water solubility decreases. 62 49 10. Carboxylic acids are weak acids. Their slight dissociation in water can be explained by the stability of the carboxylate ion caused by electron delocalisation. 63 – 64 49 500 11 Carboxylic acids can be prepared by: 72 50 499 (i) oxidising primary alcohols and aldehydes; (ii) hydrolysing nitriles, esters or amides. 533571242 Page 25 of 31 Advanced Higher Chemistry ( iii) Student Learning Outcomes Aldehydes, Ketones and Carboxylic Acids LEARNING OUTCOME 12. SCHOLAR LTS NOTES CHEM in CONTEXT 73 – 76 51 – 52 501, 504 – 505 SCHOLAR LTS NOTES CHEM in CONTEXT 82 – 83 53 84 53 516 Reactions of carboxylic acids include: (i) formation of salts by reactions with metals, carbonates and alkalis; (ii) condensation reactions with alcohols to form esters; (iii) reaction with ammonia or amines and subsequent heating of the ammonium salt to form amides; (iv) reduction with lithium aluminium hydride to form primary alcohols. PPA PPA 3: Preparation of Benzoic Acid by Hydrolysis of Ethyl Benzoate. ( iv ) Amines LEARNING OUTCOME 1. Amines are named according to I.U.P.A.C. rules. 2. Amines are organic derivatives of ammonia and can be classified as primary, secondary or tertiary. 3. Primary and secondary amines, but not tertiary amines, associate by hydrogen bonding and as a result have higher boiling points than isomeric tertiary amines and alkanes with comparable relative formula masses. 87 – 88 55 516 4. Amine molecules can hydrogen- bond with water molecules thus explaining the appreciable solubility of the lower amines in water. 89 55 517 5. The nitrogen atom in amines has a lone pair of electrons, which can accept a proton from water, producing hydroxide ions. Amines are weak bases. 90 55 519 6. Amines react with aqueous mineral or carboxylic acids to form salts. 91 – 92 55 – 56 519 533571242 Page 26 of 31 Advanced Higher Chemistry ( v) Student Learning Outcomes Aromatics LEARNING OUTCOME SCHOLAR LTS NOTES CHEM in CONTEXT 1. Bonding in benzene can be described in terms of sp2 pi () bonds, and electron delocalisation. 100 59 438 2. Benzene is the simplest aromatic hydrocarbon and its unexpected stability can be attributed to the presence of delocalised electrons. 102 59 437 – 438 3. Most reactions of benzene involve attack of an electrophile on the cloud of delocalised electrons, that is electrophilic substitution. 102 60 441 4. Benzene resists addition reactions but undergoes electrophilic substitution reactions. These include: 103 – 107 60 – 63 442 – 445 109 – 112 63 – 65 471 5. (i) chlorination and bromination to produce chlorobenzene and bromobenzene; (ii) nitration to produce nitrobenzene; (iii) sulphonation to produce benzene sulphonic acid; (iv) alkylation to produce alkylbenzenes. The presence of delocalised electrons in the phenyl group can be used to explain: (i) the stronger acidic nature of phenol compared to aliphatic alcohols; (ii) the weaker basic nature of the aromatic amine, aminobenzene (aniline),compared with aliphatic amines. 533571242 Page 27 of 31 Advanced Higher Chemistry (c) Student Learning Outcomes STEREOISOMERISM Stereoisomers have identical molecular formulae and the atoms are bonded together in the same order but the arrangement of the atoms in space is different, making them non – superimposable. ( i) Geometric Isomerism LEARNING OUTCOME SCHOLAR LTS NOTES CHEM in CONTEXT 1. Geometric isomerism is one type of stereoisomerism and can arise due to the lack of free rotation around a bond, frequently a carbon – carbon double bond. 118 68 420 2. Geometric isomers are labelled cis and trans according to whether the substituent groups are on the same side or on different sides of the carbon – carbon double bond. 119 68 420 3. Geometric isomers display differences in some physical properties. 120 69 420 4. Geometric isomerism can also influence chemical properties, for example cis -but-2- enedioic acid is more readily dehydrated than trans -but- 2- enedioic acid. 121 – 122 69 – 70 SCHOLAR LTS NOTES CHEM in CONTEXT 127 71 – 72 392 128 – 129 71 392 – 393 ( ii) Optical Isomerism LEARNING OUTCOME 1. Optical isomers are non-superimposable mirror images of each other and are said to be chiral. 2. Optical isomerism can occur in substances in which four different groups are arranged around a carbon atom. 3. Optical isomers have identical physical and chemical properties, except when they are in a chiral environment, but they have an opposite effect on plane polarised light and are said to be optically active. 132 72 392 – 393 4. Mixtures containing equal amounts of both optical isomers are optically inactive. 134 72 – 73 393 5. In biological systems only one optical isomer of each organic compound is usually present. 129 73 393 (d) STRUCTURAL ANALYSIS ( i) Elemental Microanalysis and Mass Spectroscopy SCHOLAR LTS NOTES CHEM in CONTEXT Elemental Microanalysis LEARNING OUTCOME 1. Elemental microanalysis (combustion analysis) can be used to determine the masses of C, H, S and N in a sample of an organic compound in order to find the empirical formula. 140 75 2. Other elements in the organic compound have to be determined by other methods. 140 75 533571242 Page 28 of 31 Advanced Higher Chemistry ( i) Student Learning Outcomes Elemental Microanalysis and Mass Spectroscopy Mass Spectroscopy LEARNING OUTCOME 1. Mass spectrometry can be used to determine the accurate molecular mass and structural features of an organic compound. 2. A conventional mass spectrometer functions in the following manner: The sample is firstly vaporised and then ionised by being bombarded with electrons. Fragmentation can occur when the energy available is greater than the molecular ionisation energy. The parent ion and ion fragments are accelerated by an electric field and then deflected by a magnetic field. The strength of the magnetic field is varied to enable the ions of all the different mass/ charge ratios to be detected in turn. A mass spectrum is obtained. SCHOLAR LTS NOTES CHEM in CONTEXT 142 76 2–4 142 – 143 77 2–4 144 – 148 78 383 SCHOLAR LTS NOTES CHEM in CONTEXT 166 80 385 3. Organic compounds can be identified from the very accurate determination of the relative molecular masses of the parent ion and the ion fragments. (ii) Infra – red and Nuclear Magnetic Resonance Spectroscopy and X – ray Crystallography Infra – red Spectroscopy LEARNING OUTCOME 1. Infra – red spectroscopy can be used to identify certain functional groups in an organic compound. 2. Infra-red radiation causes parts of a molecule to vibrate. The wavelengths which are absorbed and cause the vibrations will depend on the type of chemical bond and the groups or atoms at the ends of these bonds. 161 – 162 80 385 3. Infra- red radiation is passed through a sample of the organic compound and then to a detector which measures the intensity of the transmitted radiation at different wavelengths. 163 81 - 82 385 4. Infra-red spectra are expressed in terms of wavenumber. 159 80 – 81 385 5. The unit of measurement of wavenumber which is the reciprocal of wavelength is cm-1. 160 81 385 533571242 Page 29 of 31 Advanced Higher Chemistry ( ii) Student Learning Outcomes Infra – red and Nuclear Magnetic Resonance Spectroscopy and X – ray Crystallography Nuclear Magnetic Resonance Spectroscopy LEARNING OUTCOME 1. SCHOLAR LTS NOTES CHEM in CONTEXT 172 – 173 88 388 Nuclear magnetic resonance spectroscopy (nmr) can give information about: (i) the different environments of hydrogen atoms in an organic molecule; (ii) how many hydrogen atoms there are in each of these environments. 2. Hydrogen nuclei behave like tiny magnets and in a strong magnetic field some are aligned with the field (lower energy) while the rest are aligned against it (higher energy). 170 84 – 85 387 3. Absorption of radiation in the radiofrequency region of the electromagnetic spectrum will cause the hydrogen nuclei to ‘flip’ from the lower energy alignment to the higher one. As they fall back from the higher to the lower level the emitted radiation is detected. 170 – 171 85 387 4. In the nmr spectrum the peak position (chemical shift) is related to the environment of the proton. 173 86 388 5. The area under the peak is related to the number of protons in that environment. 173 88 388 – 389 6. The standard reference substance used in nmr spectroscopy is tetramethylsilane (TMS) which is assigned a chemical shift equal to zero. 172 86 388 (ii) Infra - red and Nuclear Magnetic Resonance Spectroscopy and X - Ray Crystallography SCHOLAR LTS NOTES CHEM in CONTEXT X – ray Crystallography LEARNING OUTCOME 1. X - ray crystallography can be used to determine the precise three-dimensional structure of organic compounds. 177 90 116 2. A crystal of an organic compound acts as a diffraction grating when it is exposed to X - rays of a single wavelength the atoms of the crystal act as a diffraction grating. 177 90 116 – 117 3. Electron-density maps are produced from the positions and intensities of the ‘spots’ in the diffraction pattern. 177 – 178 91 118 4. From the electron- density map the precise location of each atom in the molecule can be determined, and since heavier atoms have more electrons than lighter ones each atom in the molecule can be identified. 178 91 118 5. Since a hydrogen atom has a low electron density X-rays do not easily detect it 180 92 533571242 Page 30 of 31 Advanced Higher Chemistry (e) Student Learning Outcomes MEDICINES Drugs are substances, which alter the biochemical processes in the body, and those, which have a beneficial effect, are called medicines. ( i) Historical Development LEARNING OUTCOME SCHOLAR LTS NOTES 1. The first medicines were plant brews. 184 93 2. Pharmacologically active compounds in plant extracts were identified. 184 93 3. These compounds and derivatives of them were synthesised where practicable. 184 93 4. Aspirin is an example of a medicine developed in this way. 184 94 PPA PPA 4: Preparation of Aspirin. PPA PPA 5: Aspirin Determination. ( ii) How a Medicine Functions LEARNING OUTCOME SCHOLAR LTS NOTES Most medicines work by binding to receptors. Receptors are usually protein molecules that are either on the surface of cells where they interact with small biologically active molecules or are enzymes that catalyse chemical reactions (catalytic receptors). 186 – 188 95 1. 2. That structural fragment of the molecule which confers pharmacological activity on it is called the pharmacophore. 189 98 3. The shape of the pharmacophore complements that of the receptor site, allowing it to fit into the receptor. The functional groups on both are correctly positioned to interact and bind the medicine to the receptor. 189 98 4. By comparing the structures of medicines with similar pharmacological activity, the pharmacophore can be identified. 189 98 5. Many medicines can be classified as agonists or as antagonists according to whether they enhance or block the body’s natural responses. 187 97 6. An agonist will produce a response like the body’s natural active compound. 187 97 7. An antagonist produces no response but prevents the action of the body’s natural active compound. 188 97 533571242 Page 31 of 31 CHEM in CONTEXT CHEM in CONTEXT