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Skills The ways in which chemistry investigation skills are expressed are set out in the following table on intended student learning. Key Ideas Students should know and understand the following: Intended Student Learning Students should provide evidence that they are able to do the following: Purposes of Investigations Investigations and experiments have a clearly defined purpose. Investigations are based on existing information or issues. Before searching for information it is necessary to have a clear idea of the information required, the level of detail needed, and the appropriate facilities for extracting the information. Before undertaking an information search it is necessary to be familiar with search techniques, the way in which the information is structured, and the means of retrieving the information. State the purpose of the investigation or experiment. For a given topic, state the key ideas or issues relevant to the information required, and identify the type of resource that might provide the information. Identify key search words and phrases for a given topic. Use an information source (e.g. library catalogue, CDROM, or the Internet) to obtain information about a topic. Questions and Hypotheses Investigable questions guide investigations on chemistry issues. Formulate a question for an investigation based on a chemistry issue. Investigations are often designed to explore questions and to develop possible solutions to those questions. Suggest possible investigations to test the question. Experiments may be used to test hypotheses. State a testable hypothesis, where appropriate. Designing Investigations Design Scientific inquiry involves designing procedures, including investigations based on the scientific method or observations made in the field, to investigate questions. Designing an investigation involves identifying: what needs to be observed the measurements that need to be taken the techniques that need to be used the apparatus or measuring instruments needed. Design procedures to investigate posed questions or hypotheses. Every step in a practical or issues investigation serves a purpose. Describe the steps of an investigation. Design and carry out investigations to explore a chemistry issue. Design and carry out experiments, using the scientific method. Record and analyse observations. Draw or interpret diagrams of the apparatus used in an experiment. Variables Many practical investigations involve deliberately changing one quantity and determining the effect on another quantity. These quantities are referred to as ‘variables’. Identify the variables in a practical investigation. The quantity being deliberately changed is called the ‘independent variable’. The quantity that changes as a result, and is measured, is called the ‘dependent variable’. Classify appropriate variables in a practical investigation as independent or dependent. Other variables are held constant, if possible, throughout a practical investigation. Identify any variables that are deliberately held constant throughout a practical investigation. 26 Stage 2 Chemistry 2014 Key Ideas Students should know and understand the following: Intended Student Learning Students should provide evidence that they are able to do the following: Conducting Investigations Procedures Practical investigations require a particular set of actions to be carried out in a well-defined order. Follow instructions accurately and safely. Appropriate apparatus is selected to undertake: measurement of mass, volume, temperature, and pH volumetric analysis construction of electrochemical cells preparation of simple organic compounds. Select appropriate apparatus for the measurement of mass, volume, temperature, and pH. Prepare standard solutions, carry out dilutions, and undertake titrations. Construct galvanic and electrochemical cells. Prepare organic compounds, using distillation, reflux, and liquid–liquid extraction. Safety and Ethics Ethical practices must be followed when conducting investigations. Maintain confidentiality, report accurately, and acknowledge the work of other people. Safety must be considered when conducting investigations. Recognise hazards and work safely during a practical investigation. Many investigations involve the collaborative efforts of a team. Negotiate procedures with the other members of a team. Define the role of each member. Members of a team work together. Perform the role of a team member. Errors in Measurements Measurements are affected by random and/or systematic errors. Identify sources of errors and uncertainty that may occur in a practical investigation. Random errors are present when there is scatter in the measured values. Systematic errors are present when measured values differ consistently from the true value. Distinguish between random and systematic errors. Where applicable, increasing the number of samples minimises the effects of random errors and improves the reliability of the data. Explain the importance of increasing the number of samples in a practical investigation. Systematic errors can be identified and results verified by repeating an experiment using an alternative source of equipment and materials. Explain the importance of repeating a practical investigation where feasible. Precision, Reliability, and Accuracy The reliability/precision of data collection is related to the reproducibility of the measurements. Where possible, collect data using measurements that can be reproduced consistently. Measurements are more reliable/precise when there is less scatter in the results. Determine which of two or more measuring instruments or sets of measurements is most reliable/precise. Reliability/precision depends on the extent to which random errors are minimised. Use averages or graphing as a means of detecting or minimising the effects of random errors. The accuracy of an experimental value indicates how close the result is to the true value and depends on the extent to which systematic errors are minimised. State which result of two or more experiments is most accurate, given the true value. The resolution of a measuring instrument is the smallest increment measurable by the measuring instrument. Select an instrument of appropriate resolution for a measurement. The number of significant figures for a measurement is determined by the reproducibility of the measurement and the resolution of the measuring instrument. Record and use measurements to an appropriate number of significant figures. Stage 2 Chemistry 2014 27 Key Ideas Students should know and understand the following: Intended Student Learning Students should provide evidence that they are able to do the following: Information and Data Valid conclusions depend on gathering appropriate evidence. In investigations, make and record careful and honest observations and measurements. Practical investigations involve observations, which may be quantitative or qualitative. Distinguish between qualitative and quantitative evidence. Data can be more easily interpreted if presented in a wellstructured table. Present data in an appropriate tabular form. Include a title, column headings showing the quantities measured and the units used, and the values observed or researched. Graphs are a useful way of displaying some forms of data. When a graph is plotted, the independent variable (or a quantity derived from it) is plotted horizontally and the dependent variable (or a quantity derived from it) is plotted vertically. Plot a graph of dependent variable versus independent variable. Include a title, labelled axes, and appropriate scales and units. A line of best fit can show relationships between variables in an experiment. Draw a line of best fit through a series of points on a graph such that the plotted points are scattered evenly above and below the line of best fit. Understanding of a topic, issue, or question is enhanced, using information from different sources. Obtain information from different sources. Evidence obtained should be critically examined for accuracy and its suitability for the purpose for which it was sought. Evaluate evidence for bias, credibility, accuracy, and suitability. The source of information must be recorded so that the information is accessible to others. List the sources of information, using an appropriate format. Limit investigations to a manageable size and identify available sources of relevant information. Interpretation and Evaluation Careful observation in a practical investigation is essential for analysis and for comparison with other experiments. Describe a pattern observed in the results of an experiment. The scatter of data points above and below the line of best fit is probably due to random errors. Using the scatter in the graphs of data from similar investigations, compare the random errors. Subsequent investigations can be improved by the critical evaluation of the procedure and results. Analyse and evaluate information from a series of observations or an investigation, and suggest improvements or indicate the additional information needed. A conclusion should be written at the end of each investigation. Write a conclusion that is based on the results of an investigation and related to the question posed and the purpose of, or the hypothesis for, the investigation. Alternative Views The evidence collected through investigations may be interpreted in a variety of ways. Describe a range of alternative interpretations or points of view based on evidence, and state reasons for the selection of the preferred interpretation. Arguments can be presented for and against an issue on the basis of information selected from different sources. Construct for-and-against arguments on an issue, based on information gathered from different credible sources. Personal views must be substantiated by the evidence collected through an investigation. Present a justification of, or evidence for, a personal view. Communication Stage 2 Chemistry 2014 28 Key Ideas Intended Student Learning Students should know and understand the following: Students should provide evidence that they are able to do the following: Communication in chemistry uses specific terminology, conventions, and symbols. Use chemistry terminology, conventions, and symbols that are appropriate for the purpose of the communication. Chemical reactions can often be described by means of a chemical equation. Write appropriate chemical equations. Communication for different audiences requires the use of a format suitable for the purpose. Select the appropriate format for a particular audience. All communication needs to be well structured, well organised, and clearly presented. Present communications (oral, written, and multimedia) clearly and logically, using chemistry concepts appropriate for the audience. Written reports should state what was done and why, the results, the analysis and interpretation of the results, and the conclusions drawn from the results. Sufficient information should be included to enable the procedure to be repeated by others. Write a report of an investigation that includes a description of its purpose and experimental procedure (if designed by the student), results, analysis, interpretation, and conclusions. Multimedia presentations use minimal language and a variety of graphics to present information. Use concise language and graphics to present information. Stage 2 Chemistry 2014 29 CONTENT Stage 2 Chemistry is a 20-credit subject in which the topics are prescribed. The subject is organised so that each intended student learning is related to a key idea or concept. Within the study of these chemical ideas and concepts, students develop their chemistry investigation skills through practical investigations and other learning activities. Topics and Subtopics Topic 1: Elemental and Environmental Chemistry 1.1 1.2 1.3 1.4 1.5 1.6 The Periodic Table Cycles in Nature The Greenhouse Effect Acid Rain Photochemical Smog Water Treatment Topic 2: Analytical Techniques 2.1 2.2 2.3 Volumetric Analysis Chromatography Atomic Spectroscopy Topic 3: Using and Controlling Reactions 3.1 3.2 3.3 3.4 3.5 3.6 3.7 Measuring Energy Changes Fuels Electrochemistry Rate of Reaction Chemical Equilibrium Chemical Industry Metal Production Topic 4: Organic and Biological Chemistry 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 4.10 4.11 Systematic Nomenclature Physical Properties Alcohols Aldehydes and Ketones Carboxylic Acids Amines Esters Amides Proteins Triglycerides Carbohydrates Stage 2 Chemistry 2014 33 Topic 5: Materials 5.1 5.2 5.3 Polymers Silicates Cleaning Agents Stage 2 Chemistry 2014 34 Topic 1: Elemental and Environmental Chemistry This topic deals with some of the underlying principles of chemistry (‘elemental chemistry’) and then considers the chemistry of the environment. The elemental chemistry component of the topic focuses on the periodic table and the concept of electronegativity; together these underlie most of the other topics in this subject outline. The environmental chemistry component focuses on a small number of inorganic molecular substances and their impacts on the environment. When the chemical elements are arranged in a periodic table, similarities and trends in properties become apparent. This topic examines the properties of compounds and elements; these properties can be explained in terms of the electronegativities of the elements and their positions in the periodic table. In the last hundred years, concern about the effects of humans on the environment has extended from the local to the global scale. Students are often exposed to environmental issues, sometimes in emotive ways. In this topic students are exposed to factual information and consider the causes of and solutions to environmental problems. 1.1 The Periodic Table Key Ideas Intended Student Learning The arrangement of electrons in any atom can be described in terms of shells and subshells. Write, using subshell notation, the electron configuration of an atom or monatomic ion of any of the first thirty-eight elements in the periodic table. The position of an element in the periodic table reflects its electron configuration. Identify the s, p, d, and f block elements in the periodic table. The periodic table is the unifying framework for the study of the chemical elements and their compounds. Elements within each group of the periodic table have similar chemical properties that can be explained in terms of their similar outer-shell electron configurations. Predict the following properties of the s and p block elements of any of the first thirty-eight elements in the periodic table: metal, metalloid, or non-metal nature of the element charge of the monatomic ions likely oxidation number(s) of the element in its compounds (including octet expansion for phosphorus, sulfur, and chlorine). The electronegativities of non-metallic atoms are higher than those of metals; non-metallic atoms tend to gain electrons in chemical reactions. Find regions in the periodic table with elements of high, intermediate, and low electronegativity. The trend from metallic to non-metallic behaviour across a period is related to the increase in electronegativity. These trends are reflected in changes in the acidic/basic character of the oxides. Predict the acidic/basic character of the oxides of an element from the position of the element in the periodic table. The oxides of non-metals are acidic. Their acidic character can be displayed by reaction with hydroxide ions to produce an oxyanion and, in most cases, by reaction with water to produce an oxyacid. Write equations for the reactions of oxides of nonmetals such as SiO2, CO2, SO2, SO3, and P4O10 with hydroxide ions and with water, where a reaction occurs. The oxides of metals are basic. Their basic character can be displayed by reaction with an acid to produce a cation and, in some cases, by reaction with water to produce OH in solution. Write equations for the reactions of oxides of metals such as MgO, Na2O, CuO, and Fe2O3 with acids and with water, where a reaction occurs. Metalloids form amphoteric oxides. Amphoteric oxides can display basic character by reaction with hydrogen ions and acidic character by reaction with hydroxide ions. Write equations for the reactions of amphoteric oxides such as Al2O3 and ZnO with hydrogen ions or hydroxide ions. Small molecules are formed from elements in a small section of the periodic table. Small molecules are those either of nonmetallic elements or of compounds of non-metallic elements. Predict whether or not a compound or element is likely to be molecular, given its properties, name, elemental composition, or formula. Atoms in a molecule are bound strongly to each other by covalent bonds. Molecules interact weakly with each other. Compare the strengths of covalent bonds with the strengths of secondary interactions. Stage 2 Chemistry 2014 35 Key Ideas 1.2 The strengths of secondary interactions between non-polar molecules depend on their molar mass. Explain the higher melting points and boiling points of substances of large molar mass. The shape of molecules can be explained and predicted by repulsion between pairs of bonding and non-bonding electrons. Draw diagrams showing covalent bonds, non-bonding pairs, and shapes for three-element molecules and two-element ions containing no more than five atoms. Examples that involve valence shell octet expansion are limited to PO43 tetrahedra, SO2 , and SO3. The polarity of a molecule results from the polar character of the bonds and their spatial arrangement. Predict whether or not a molecule is polar, given its spatial arrangement. The strengths of secondary interactions between molecules of similar molar mass depend on the polarity of the molecules. Explain the higher melting points and boiling points of polar substances compared with those of non-polar substances of similar molar mass. Molecules containing N–H or O–H groups can form hydrogen bonds to N or O atoms in other molecules. Describe, with the aid of diagrams, hydrogen bonding between molecules. Cycles in Nature Key Ideas 1.3 Intended Student Learning The presence (aerobic conditions) or absence (anaerobic conditions) of oxygen affects the products of the decomposition of the organic compounds derived from living organisms. State, for aerobic and anaerobic conditions, the products of the decomposition of organic matter containing carbon, nitrogen, phosphorus, or sulfur. Photosynthesis and respiration are important processes in the cycles of carbon and oxygen. Describe and write equations for the processes of photosynthesis and aerobic respiration involving glucose. Nitrogen may be converted into compounds by biological processes such as fixation or by reaction with oxygen during lightning discharges and at high temperatures such as those which occur in engines and furnaces. Describe and write equations for the formation of oxides of nitrogen by the reaction of nitrogen and oxygen at high temperatures. Nitrogen compounds are important in the chemistry of life processes. Describe how the nitrogen cycle operates by natural processes (e.g. lightning, nitrogen-fixing bacteria, and decay) and industrial processes (e.g. fertiliser manufacture and combustion engines). Plants require substantial amounts of nitrogen and phosphorus, which they obtain from the soil. Explain why fertilisers need to contain nutrients in soluble form. The Greenhouse Effect Key Ideas 1.4 Intended Student Learning Intended Student Learning Some gases in the atmosphere, called ‘greenhouse gases’, serve as insulation to maintain the temperature of the Earth’s atmosphere. This is known as the ‘natural greenhouse effect’. Describe the action of the common greenhouse gases, carbon dioxide and methane, that serve to maintain a steady temperature in the Earth’s atmosphere. Human activity that affects the concentration of greenhouse gases has the potential to disrupt the thermal balance of the atmosphere. This is known as the ‘enhanced greenhouse effect’. Explain the enhanced greenhouse effect and its potential consequences for the environment. Acid Rain Stage 2 Chemistry 2014 36 Key Ideas 1.5 Intended Student Learning pH is a measure of the concentration of hydrogen ions: i.e. pH log [H+]. Calculate the concentration of H+ and OH of solutions, given their pH, and vice versa. Rain containing dissolved carbon dioxide is acidic. Write equations to show how carbon dioxide produces acidic rain. Rainfall with a pH of less than 5.6, known as ‘acid rain’, is formed when oxides of nitrogen and sulfur dissolve in water in the atmosphere. Describe and write equations for the formation of acid rain. Acid rain has harmful environmental effects. Describe the environmental effects of acid rain, including its action on metals and carbonates (with equations) and on the mobilisation of toxic cations such as aluminium. The low pH of acid rain is due to the presence of sulfuric and nitric acids. Calculate the pH of solutions of strong bases and strong monoprotic acids. Photochemical Smog Key Ideas 1.6 Intended Student Learning Nitrogen oxides are formed in high-temperature engines and furnaces. Write equations for the formation of nitrogen oxides NO and NO2. Nitrogen oxides lead to the formation of ozone in the troposphere. Describe and write equations showing the role of nitrogen oxides in the formation of ozone in the troposphere. Nitrogen oxides and ozone in the troposphere are pollutants. Explain the terms ‘primary pollutants’ and ‘secondary pollutants’ with reference to the harmful effects of nitrogen oxides and ozone in the troposphere. It is possible to reduce the quantities of nitrogen oxides generated by cars. Describe how catalytic converters reduce the quantities of nitrogen oxides generated by cars. Water Treatment Key Ideas Intended Student Learning Suspended matter is removed from water by flocculation followed by sedimentation or filtration. Describe the use of aluminium ions in the removal of suspended matter from water. Hypochlorous acid, chlorine, and hypochlorites are used for water purification. State that hypochlorous acid, chlorine, and hypochlorites kill bacteria by their oxidising action. Chlorine is used for water purification. Explain the effect of pH on the equilibrium between chlorine, water, and hydrochloric acid and hypochlorous acid. Stage 2 Chemistry 2014 37 Topic 2: Analytical Techniques Chemists perform a wide variety of monitoring roles, including analysing for drug residues and measuring the concentrations of pollutants such as pesticides in the environment. Chemists are also employed to analyse materials used in or produced by many branches of industry, including pharmaceuticals, polymers, metal production, and food preparation. In this topic students consider some of the more common means of analysis and undertake practical activities in measurement. 2.1 Volumetric Analysis Key Ideas Intended Student Learning Concentrations of solutes in solutions can be described by using a number of standard conventions. Convert concentrations from one unit to another (e.g. mol L1, g L1, %w/v, ppm, and ppb). Knowledge of the mole ratios of reactants can be used in quantitative calculations. Perform stoichiometric calculations when given the reaction equation and the necessary data. A titration can be used to determine the reacting volumes of two solutions. Describe the correct use of a volumetric flask, a pipette, and a burette. Analysis of a variety of chemicals depends on an understanding of quantitative aspects of chemical reactions, including acid–base and redox reactions. Describe and explain the procedure involved in carrying out a titration, particularly rinsing glassware and determining the end-point. A titration can be used to determine the concentration of a solution of a reactant in a chemical reaction. Determine the concentration of a solution of a reactant in a chemical reaction by using the results of a titration. 2.2 Chromatography Key Ideas Intended Student Learning Adsorption chromatography involves the use of a stationary phase and a mobile phase to separate the components of a mixture. Identify the stationary and mobile phases in an adsorption chromatography process. The strength of attraction between two substances depends on their relative polarities. Predict the relative strengths of attraction of components for the stationary phase and the mobile phase on the basis of their polarities. The rate of movement of any component along a stationary phase is determined by the structure or relative polarity of the component and the relative polarities of the stationary phase and the mobile phase. Predict the relative rates of movement of components along a stationary phase, given the structural formulae or relative polarities of the components and the two phases. The rate of movement of a component along a stationary phase is compared with a known standard in order to identify the component. Describe and apply RF values and retention times in the identification of components in a mixture. 2.3 Atomic Spectroscopy Key Ideas Intended Student Learning Electrons move to a higher or lower energy level when atoms or ions absorb or emit radiation. State the effect of the absorption or emission of radiation on the energy levels of electrons in atoms or ions. The wavelengths of radiation emitted and absorbed by an element are unique to that element. State that the wavelengths of radiation emitted and absorbed by an element are unique to that element. The wavelengths of radiation absorbed by an element can be used to identify its presence in a sample. Explain the principles of atomic absorption spectroscopy in identifying elements in a sample. Atomic absorption spectroscopy is used for quantitative analysis. Describe the construction and use of calibration graphs in determining the concentration of an element in a sample. Stage 2 Chemistry 2014 38 Topic 3: Using and Controlling Reactions The use and control of chemical reactions are important tasks undertaken by chemists. This topic looks at the energy changes that accompany chemical reactions and their rates and extents. It also examines the ways in which chemical reactions are controlled and used to make materials and generate the energy needed by a modern industrial society. The increased use of energy from chemical reactions has been a major factor in the development of the industrialised world. In this topic students consider the ways in which this energy is produced and begin quantitative consideration of the energy changes that accompany chemical reactions. The production of chemicals is the main function of the chemical industry. These chemicals allow naturally occurring materials to be modified or replaced, and previously unknown materials to be developed. The industrialised world depends on the chemical industry for the manufacture of a diverse range of materials. In this topic students look at how chemicals are produced and how the production can be performed most efficiently. Knowledge of chemistry can be applied to manipulate the reaction conditions of industrial processes in order to determine the quantity or quality of the product. 3.1 Measuring Energy Changes Key Ideas Intended Student Learning Almost all chemical reactions occur with either an absorption or a release of heat or light energy. Other forms of energy, such as electrical energy, can also be released. Identify combustion and respiration as reactions that release energy and photosynthesis as a reaction that absorbs energy. Exothermic reactions release energy to the surroundings, whereas endothermic reactions absorb energy from the surroundings. Deduce whether a reaction is exothermic or endothermic from information provided. The measurement of the heat change in chemical reactions is called ‘calorimetry’; the insulated apparatus used for the measurement is a calorimeter. Calculate the heat released or absorbed for a reaction from experimental data, given the specific heat capacity of water (4.18 J g1 K1). The heat released or absorbed in a reaction at constant pressure is called the ‘enthalpy change for the reaction’; it is represented by the symbol H. Determine enthalpy changes from experimental data for reactions, including: the combustion of alcohols the neutralisation of acids with bases solution processes. Exothermic reactions have negative H values. Endothermic reactions have positive H values. Identify a reaction as exothermic or endothermic, given a thermochemical equation or the value of its enthalpy change. Thermochemical equations express a quantitative relationship between the quantities of reactants and the enthalpy change. Write thermochemical equations that correspond to given molar enthalpies of combustion, neutralisation, and solution. The magnitude of the heat absorbed or evolved for a reaction is directly proportional to the quantities of reactants involved. Calculate the theoretical temperature change of a specified mass of water or solution heated or cooled by a reaction, given molar enthalpies and quantities of reactants. 3.2 Fuels Key Ideas Intended Student Learning Carbon-based fuels provide energy and are feedstock for the chemical industry. Describe the advantages and disadvantages of the use of carbon-based fuels as sources of heat energy, compared with their use as feedstock. Carbon dioxide and water are produced by the complete combustion of compounds containing carbon and hydrogen. Write balanced equations for the complete combustion of fuels in which the only products are carbon dioxide and water. Stage 2 Chemistry 2014 39 Key Ideas Intended Student Learning The products of the incomplete combustion of carbon-based fuels include carbon (soot) and carbon monoxide. Soot and carbon monoxide are harmful to the environment. Describe the undesirable consequences of incomplete combustion. Fuels can be compared on the basis of the quantity of heat released. Calculate the quantities of heat evolved per mole, per gram, and per litre (for liquids) for the complete combustion of fuels. 3.3 Electrochemistry Key Ideas Intended Student Learning Electrochemical cells are conveniently divided into galvanic cells, which produce electrical energy from spontaneous redox reactions, and electrolytic cells, which use electrical energy from an external source to cause a non-spontaneous chemical reaction. Identify a cell as galvanic or electrolytic, given sufficient information. Redox reactions can be considered as two half-reactions, one involving oxidation and the other reduction. Write half-equations for half-reactions, including those in acidic solution, given information about the reactants and the products. Galvanic and electrolytic cells involve oxidation at the anode and reduction at the cathode, with electrons being transferred from one electrode to the other through an external circuit. Identify the anode and cathode in a galvanic cell or an electrolytic cell, given information about the reactants and the products. Galvanic cells are commonly used as portable sources of electric currents. Identify the: charge on the electrodes direction of electron flow movement of ions in the salt bridge or electrolyte given a sketch for a galvanic cell and information about electrode reactions. Fuel cells are galvanic cells in which the electrode reactants are available in continuous supply. State the advantages and disadvantages of fuel cells compared with other galvanic cells. Some galvanic cells can be recharged by using an external electrical supply to reverse the electrode reactions. Describe the complementary nature of the charging and discharging of rechargeable galvanic cells. Electrolytic cells are used in the production of active metals. Describe, with the aid of equations, the electrolytic production of active metals. 3.4 Rate of Reaction Key Ideas Intended Student Learning The time taken for a reaction to reach a specified point is an indication of the rate of the reaction. Determine the effect of varying conditions on the rate of a given reaction, using experimental data. The rates of a reaction at different times can be compared by considering the slope of a graph of quantity (or molar concentration) of reactant or product against time. Draw and interpret graphs representing changes in quantities or concentration of reactants or products against time. The rates of a reaction are affected by changes in the: concentration of reactants temperature of the reaction mixture pressure of the reaction mixture (for systems involving gases) state of subdivision of reactants presence of catalysts (including enzymes) intensity of light (for photochemical reactions). Predict and explain the effect that changes in condition have on the rates of reactions in terms of the: frequency of collisions between reactant particles orientation of colliding particles energy of colliding particles activation energy. Stage 2 Chemistry 2014 40 Key Ideas Intended Student Learning The energy changes in a reaction can be represented by an energy profile diagram. 3.5 Draw and interpret energy profile diagrams that show the relative enthalpies of reactants and products, the activation energy, and the enthalpy change for the reaction. Chemical Equilibrium Key Ideas Intended Student Learning All chemical reactions carried out in a closed system at a fixed temperature eventually reach a state of dynamic equilibrium in which the concentrations of all the reactants and products cease to change with time. The total mass of reactants and products in a closed system remains constant. Describe the dynamic nature of a chemical system at equilibrium. The position of equilibrium in a chemical system at a given temperature can be indicated by a constant, Kc, related to the concentrations of reactants and products. Write Kc expressions that correspond to given reaction The changes in concentrations of reactants and products as a system reaches equilibrium can be represented graphically. Draw and interpret graphs representing changes in concentration of reactants and products against time. The final equilibrium concentrations for a given reaction depend on the: initial concentrations of the reactants and products temperature Calculate the initial and/or equilibrium concentrations or quantities of reactants and products, given sufficient information about a particular system initially and/or at equilibrium. equations, and perform calculations involving Kc and equilibrium concentrations in which all reacting species are included in the expression. value of Kc pressure (for systems involving gases). If a change is made to a system at equilibrium so that it is no longer at equilibrium, a net reaction will occur (if possible) in the direction that counteracts the change. This is a statement of Le Châtelier’s principle. Predict, using Le Châtelier’s principle, the effect on the equilibrium position of a system of a change in the: concentration of a reactant or product overall pressure of a gaseous mixture temperature of an equilibrium mixture for which the H value for the forward or back reaction is specified. 3.6 Chemical Industry Key Ideas Intended Student Learning In any industrial chemical process it is necessary to select conditions that will give maximum yield in a short time. This will often involve compromises between conditions that produce the maximum rate, conditions that produce the maximum yield, and costs. Explain the reaction conditions that will maximise yield. The steps in industrial chemical processes can be conveniently displayed in flow charts. Interpret flow charts and use them for such purposes as identifying: raw materials; chemicals present at different steps in the process; waste products; and by-products. 3.7 Metal Production Key Ideas Stage 2 Chemistry 2014 Intended Student Learning 41 Key Ideas Intended Student Learning The likelihood that an uncombined metal will occur naturally increases with lack of reactivity. Predict whether a metal is likely to occur in nature uncombined or combined with other elements, given the relative position of the metal in a table of metal reactivities. The stages in the production of metals from their ores include concentration of the mineral; conversion of the mineral into a compound suitable for reduction; reduction; and refinement of the metal. Identify the stages in the production of a metal from its ore and explain why not all stages are necessary in the production of some metals. The stages in the electrolytic production of zinc from its ore are concentration of the zinc mineral; conversion of the zinc mineral into a form suitable for reduction; and electrolytic reduction. Describe, with the aid of equations, the production of zinc from its ore. Electrolysis of molten electrolyte is used in the reduction stage for the production of more reactive metals. Explain why the production of aluminium requires a molten nonaqueous electrolyte. Reduction of the oxide using carbon can be used for the production of less active metals. Explain why zinc and iron can be obtained by reduction using carbon whereas this is not possible for aluminium. The method used in the reduction stage in the production of a metal is related to the reactivity of the metal. Predict the likely method of reduction of a metal compound to the metal, given the position of the metal in the activity series of metals. Energy cost is a factor taken into account in the production of all metals. Explain why reduction using electrolysis of an aqueous solution is preferable to electrolysis of a melt. Stage 2 Chemistry 2014 42 Topic 4: Organic and Biological Chemistry Most chemicals are compounds of carbon with other elements, mainly hydrogen, oxygen, and nitrogen, with many more being synthesised each year. The variety and importance of carbon compounds are so great that there is a specific branch of chemistry known as ‘organic chemistry’. In this topic students are introduced to the chemistry of the more common organic compounds. Biological chemistry is a growing area of research; it includes medical technology, genetic engineering, and the development of pharmaceuticals. In this topic students are introduced to the major groups of compounds of biological significance. The reactions of the larger macromolecules can often be explained by referring to the reactions and properties of smaller molecules with the same functional groups. 4.1 Systematic Nomenclature Key Ideas Intended Student Learning The presence or absence of functional groups in an organic compound determines its physical and chemical properties. Identify the functional groups in the structural formulae of alcohols, aldehydes, ketones, carboxylic acids, amines, esters, and amides. Organic compounds are named systematically to provide unambiguous identification. State, given its structural formula, the systematic name of an organic compound containing: up to eight carbon atoms arranged as either a straight chain or a branched chain one or more of the same functional groups (with these limited to hydroxyl, aldehyde, ketone, carboxyl, or primary amino groups). The structural formula of an organic compound can be deduced from its systematic name. Given its systematic name, draw the structural formula of an organic compound containing: up to eight carbon atoms arranged as either a straight chain or a branched chain one or more of the same functional groups (with these limited to hydroxyl, aldehyde, ketone, carboxyl, or primary amino groups). Esters are named as derivatives of a carboxylic acid. State the systematic names of methyl and ethyl esters of straight-chain acids containing up to eight carbon atoms. The structural formula of an ester can be deduced from its systematic name. Given its systematic name, draw the structural formula of an organic methyl or ethyl ester of a straight-chain acid containing up to eight carbon atoms. 4.2 Physical Properties Key Ideas Intended Student Learning The melting points and boiling points of organic compounds that contain the same functional group increase with the length of carbon chain. Predict and explain the melting points and boiling points of an organic compound in comparison with those of other compounds that contain the same functional group. The boiling points of organic compounds that display hydrogen bonding between molecules are higher than those of compounds of similar molar mass that do not display hydrogen bonding. Predict and explain the boiling points of alcohols in comparison with those of aldehydes and ketones of similar molar mass. The boiling points of esters are lower than those of isomeric acids because of the absence of hydrogen bonding between molecules of the ester. Predict and explain the boiling points of esters in comparison with those of isomeric acids. Organic compounds are generally insoluble in water. Explain the insolubility in water of most organic compounds. Stage 2 Chemistry 2014 43 Key Ideas Intended Student Learning Hydrogen bonding between functional groups and water can explain the solubility in water of some smaller organic compounds. Predict and explain the solubility in water of the smaller amino acids, carboxylic acids, alcohols, aldehydes, and ketones. The solubility in water of an organic compound depends on its molar mass and the functional groups present. Predict and explain the relative solubilities in water of two organic compounds, given their structural formulae. 4.3 Alcohols Key Ideas 4.4 Ethanol is produced by the fermentation of glucose, which can be derived by the hydrolysis of complex carbohydrates. Describe the conditions, and write equations, for the hydrolysis of polysaccharides and disaccharides, and the production of ethanol by the fermentation of glucose. Alcohols are classified as primary, secondary, or tertiary. Identify a hydroxyl group in an alcohol as primary, secondary, or tertiary, given the structural formula. Primary and secondary alcohols can be distinguished from tertiary alcohols by their reaction with acidified dichromate solution. Describe how primary and secondary alcohols can be distinguished from tertiary alcohols by their reaction with acidified dichromate solution. The type of product obtained by oxidising an alcohol depends on whether the alcohol is primary or secondary. Predict the structural formula(e) of the product(s) of dichromate oxidation of a primary or secondary alcohol, given its structural formula. Aldehydes and Ketones Key Ideas 4.5 Intended Student Learning Intended Student Learning Aldehydes and ketones are produced by the oxidation of the corresponding primary and secondary alcohols respectively. Aldehydes are readily oxidised and so must be distilled off from the reaction mixture as they are formed. Given the structural formula of the aldehyde or ketone, draw the structural formula of the alcohol from which it could be produced by oxidation, and describe the necessary reaction conditions. Aldehydes can be oxidised to form carboxylic acids or, in alkaline solutions, carboxylate ions. Draw the structural formula of the oxidation product of a given aldehyde in either acidic or alkaline conditions. Ketones cannot readily be oxidised. This difference in properties between aldehydes and ketones can be used to distinguish one from the other. Describe how acidified dichromate solution and Tollens’ reagent (ammoniacal silver nitrate solution) can be used to distinguish between aldehydes and ketones. Carboxylic Acids Key Ideas Intended Student Learning Carboxylic acids can be produced by the oxidation of aldehydes or primary alcohols. Identify the aldehyde or primary alcohol from which a carboxylic acid could be produced by oxidation, given its structural formula. Carboxylic acids are weak acids and, to a small extent, ionise in water. Write an equation for the ionisation of a carboxylic acid in water. Carboxylic acids react with bases to form ionic carboxylate salts. Write equations for the reactions of carboxylic acids with hydroxides, carbonates, and hydrogencarbonates, and describe changes that accompany these reactions. Stage 2 Chemistry 2014 44 Key Ideas Intended Student Learning The salts of sodium and potassium carboxylates are soluble in water because of the ion–dipole attraction between the ions and water. 4.6 Explain why some drugs with carboxyl groups are usually taken in the form of their salts. Amines Key Ideas Intended Student Learning Owing to the presence of an unbonded electron pair, amines are able to act as bases and accept H+ ions. Draw the structural formula of the protonated form of an amine, given the structural formula of its molecular form, and vice versa. Amines are classified as primary, secondary, or tertiary. Identify an amino group in an amine as primary, secondary, or tertiary, given the structural formula. The salts of amines are soluble in water because of the ion–dipole attraction between the ions and water. Explain why some drugs with amine groups are usually taken in the form of their salts. 4.7 Esters Key Ideas Intended Student Learning An ester can be produced by a condensation reaction between an alcohol and a carboxylic acid. Draw the structural formula of the ester that could be produced by the condensation reaction between an alcohol and a carboxylic acid, given their structural formulae, and write an equation for the reaction. The production of an ester from the reaction of an alcohol and a carboxylic acid is slow at 25°C. Explain the use of heating under reflux and the presence of a trace of concentrated sulfuric acid in the laboratory production of esters. Esters may be hydrolysed under acidic or alkaline conditions. Identify the products of hydrolysis of an ester, given its structural formula. 4.8 Amides Key Ideas Intended Student Learning An amide can be produced by a condensation reaction between an amine and a carboxylic acid. Draw the structural formula of the amide that could be produced by the condensation reaction between an amine and a carboxylic acid, given their structural formulae. Amides may be hydrolysed under acidic or alkaline conditions. Identify the products of hydrolysis of an amide, given its structural formula. 4.9 Proteins Key Ideas Intended Student Learning Amino acids contain a carboxyl group and an amino group. Determine whether or not a compound is an amino acid, given its structural formula. Amino acids can self-ionise to produce an ion. Draw the structural formula of the product formed when an amino acid self-ionises. Proteins are large molecules in which amide groups link monomer units. In proteins the amide group is called a ‘peptide link’ or a ‘peptide bond’. Identify the amide group and deduce the structural formula(e) of the monomer(s), given the structural formula of a section of a protein. Stage 2 Chemistry 2014 45 Key Ideas Intended Student Learning Proteins are polyamides consisting of covalently bonded long chains of amino acid units. Write the general formula of amino acids and recognise their structural formulae. Proteins have sites that allow hydrogen bonding between sections of chains and between the chain and water. Identify where hydrogen bonding can occur between protein chains or between the chain and water, given the structural formula of a section of the chain. The biological function of a protein is a consequence of its unique spatial arrangement. Explain why the biological function of a protein (e.g. an enzyme) is altered if its spatial arrangement is altered. Changes in pH and temperature disrupt the secondary interactions, and hence the spatial arrangements, of a protein chain. Explain why proteins are sensitive to changes in pH and temperature. 4.10 Triglycerides Key Ideas Intended Student Learning Edible oils and fats are esters of propane-1,2,3-trio (glycerol) and various carboxylic acids. The carboxylic acids are unbranched and usually contain an even number of carbon atoms between twelve and twenty. Draw the structural formula of an edible oil or fat, given the structural formula(e) of the carboxylic acid(s) from which it is derived. Triglycerides can be hydrolysed to produce propane-1,2,3triol and various carboxylic acids. Identify the alcohol and acid(s) from which a triglyceride is derived, given its structural formula. Edible oils are liquids at 25°C and are commonly obtained from plants and fish. Edible fats are solids at 25°C and are commonly obtained from land animals. Identify the most likely source of a triglyceride, given its state at 25°C. Most liquid triglycerides contain a larger proportion of unsaturated carbon chains than solid triglycerides contain. Describe and explain the use of a solution of bromine or iodine to determine the degree of unsaturation of a compound. Draw the structural formula of the reaction product. Liquid triglycerides can be converted into triglycerides of higher melting point by a process that involves the addition of hydrogen under pressure and at increased temperature, in the presence of a catalyst. Explain the role of pressure, temperature, and a catalyst in the hydrogenation of liquid triglycerides. 4.11 Carbohydrates Key Ideas Intended Student Learning Carbohydrates are naturally occurring sugars and their polymers. They usually have the general formula CxH2yOy. They are defined more precisely as either polyhydroxy aldehydes or polyhydroxy ketones, or their polymers. Given its structural formula, determine the molecular formula of an organic compound, and whether or not it is a carbohydrate. Carbohydrates can be classified as monosaccharides, disaccharides, or polysaccharides. Write molecular formulae for glucose, and for disaccharides and polysaccharides based on glucose monomers. Polysaccharides are produced by the condensation of many monosaccharide units linked in chains by covalent bonds. Identify the repeating unit and draw the structural formula of the monomer, given the structural formula of a section of a polysaccharide derived from one monomer. Glucose molecules can occur in either a chain form or a ring form. There is equilibrium between the two structures. In the chain form an aldehyde group is present. Explain the ability of glucose to react as an aldehyde when in chain form but not when in ring form. Stage 2 Chemistry 2014 46 Key Ideas Many simple carbohydrates are soluble in water, whereas polysaccharides are insoluble in water. Stage 2 Chemistry 2014 Intended Student Learning Explain the differences in solubility in water of simple carbohydrates and polysaccharides in terms of the size of the molecules and the number of hydroxyl groups. 47 Topic 5: Materials In this topic students consider the chemical and physical properties of a range of materials and develop an understanding of the chemistry behind these properties. Polymers are important in nature and synthetic polymers represent one of the benefits of scientific advances. Silicates and aluminosilicates are the most common materials in the Earth’s crust. They form the basis of rocks and most minerals and are the major components of soils. The silicates of which they are composed determine the soils’ chemical properties. Healthy soils are essential for sustainable food production. Cleaning agents are familiar household chemicals that help in the maintenance of a healthy lifestyle. They function in a variety of ways that include dissolving, suspension, and oxidation. 5.1 Polymers Key Ideas Intended Student Learning The production of synthetic polymers allows the manufacture of materials with a diverse range of properties. Discuss the advantages and disadvantages of synthetic polymers. Polymers or macromolecules are very large molecules composed of small repeating structural units. Identify the repeating unit of a polymer, given the structural formula of a section of a chain. Polymers are produced from small molecules (monomers) by one of two main polymerisation reactions: addition or condensation. Identify a polymer as being the product of an addition polymerisation or a condensation polymerisation, given its structural formula. Addition polymerisation occurs when monomer molecules link without the loss of atoms. The monomer usually has at least one carbon–carbon double bond per molecule. Draw the structural formula of an addition polymer that could be produced from monomers containing one carbon–carbon double bond, given the structural formula(e) of the monomer(s), or vice versa. Polyesters and polyamides are large molecules in which monomer units are linked by ester and amide groups respectively. Identify the ester group in a polyester and the amide group in a polyamide. Condensation polymerisation occurs when one or more compounds (such as water) are produced as the monomer molecules link. Draw the structural formula(e) of the polyester or polyamide polymers that could be produced from monomers, given the structural formula(e) of the monomer(s), or vice versa. Organic polymers can have different properties, such as rigidity, depending on the monomers and the degree of crosslinking between chains. Describe the effect on rigidity of increasing the number of primary and secondary interactions between polymer chains. Heat affects thermoplastic and thermoset polymers differently. Describe the effects of heating on thermoplastic and thermoset polymers, and the consequent difference in the ease of recycling. 5.2 Silicates Key Ideas Intended Student Learning Silicon dioxide, silicates, and aluminosilicates are important components of rocks and soils. Write the formula of the anion in a silicate or aluminosilicate, given its formula. The structure of silicates is based on SiO4 tetrahedra. Identify the SiO4 structural unit in diagrams of silicate anions. In silicates, oxygen atoms can be shared between two SiO4 tetrahedra. Draw the repeating unit and write the formula of an extended silicate anion, given its structural formula. In silicates the oxidation state of silicon is 4 whereas that of oxygen is 2. State the charge on a silicate anion, given the Si:O ratio. The charge balance in silicate minerals is achieved by the presence of cations, most commonly Ca2+, Mg2+, K+, Na+, Fe2+, and Fe3+. Write the formula of a silicate mineral, given the structural formula of the silicate anion and the metal ions present. Stage 2 Chemistry 2014 48 Key Ideas Intended Student Learning In minerals known as ‘aluminosilicates’, aluminium atoms replace some of the silicon atoms. State the charge of an aluminosilicate ion, given its formula. Cations held on the surface of soil silicates are in equilibrium with the cations in soil water, which are available as sources of plant nutrients. Explain how cations held on the surface of soil silicates are made available to plants. Soil silicates are able to adsorb H+ in the soil water and release cations. Describe the effect of acid rain in releasing cations from soil silicates. The surface of fine silicate particles in clays is negatively charged and can be flocculated into larger particles by the addition of salts containing highly charged cations such as aluminium ions. Explain the use of aluminium ions in flocculating clay particles suspended in water. Silicates such as zeolites are able to soften water by the exchange of cations. Explain the use of silicates in water softeners. 5.3 Cleaning Agents Key Ideas Intended Student Learning Many stains can be removed by the use of an appropriate solvent. Describe the use of non-polar solvents to dissolve nonpolar materials and the use of polar solvents to dissolve polar materials. Soaps and synthetic sulfonate detergents consist of a nonpolar hydrocarbon chain, which is hydrophobic, and an ionic region, which is hydrophilic. Describe and explain how soaps and synthetic sulfonate detergents remove grease. Fats and oils can be hydrolysed by boiling with sodium hydroxide solution. The carboxylate salts formed are soaps. Write equations for the alkaline hydrolysis of triglycerides. Soaps form an insoluble material when used in hard water. Write an equation for the formation of magnesium or calcium precipitate from soap, given the structural formula of the soap anion. The effectiveness of soaps is significantly reduced when they are used in hard water, whereas the effectiveness of synthetic detergents is not greatly changed when they are used in hard water. Describe how the reaction of soap with hard water differs from that of synthetic detergents. The structure of phosphates is based on PO4 tetrahedra. Draw the structural formula of the PO43 ion. In tripolyphosphates, oxygen atoms can be shared between PO4 tetrahedra. Draw the structural formulae of linear and cyclic tripolyphosphate ions. Tripolyphosphates are added to many detergent formulations. Explain how tripolyphosphate ions keep: calcium and magnesium ions in solution; clay particles in suspension; and pH mildly alkaline. Tripolyphosphates improve the effectiveness of detergent formulations. Explain the importance of the actions of tripolyphosphate ions. Phosphates can cause eutrophication in water bodies. Describe the advantages and disadvantages of the use of phosphate fertilisers and polyphosphates in detergent formulations. Chlorine bleaches are most stable at a pH above 7. Explain the effect of lowering pH on the decomposition of hypochlorites to chlorine. Enzymes are added to some detergent formulations. Describe the use of enzymes in detergents and explain why they are sensitive to changes in pH and temperature. Stage 2 Chemistry 2014 49 Key Ideas Intended Student Learning Solid oxygen bleaches release hydrogen peroxide as an oxidising agent. Hydrogen peroxide decomposes to release oxygen. Use the change in oxidation number of oxygen to show hydrogen peroxide and oxygen acting as oxidising agents. Solid oxygen bleaches are added to some detergent formulations because they release hydrogen peroxide and hence oxygen in solution. Describe how solid oxygen bleaches release oxidising agents when dissolved in water. Stage 2 Chemistry 2014 Explain why the effectiveness of solid oxygen bleaches is affected by changes in temperature. 50