Chemistry (Version 8.4)

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Understand how Chemistry works

Rationale/Aims

Chemistry is the study of materials and substances, and the transformations they undergo through interactions and the transfer of energy. Chemists can use an understanding of chemical structures and processes to adapt, control and manipulate systems to meet particular economic, environmental and social needs.

Structure of Chemistry

In Chemistry, students develop their understanding of chemical systems, and how models of matter and energy transfers and transformations can be used to describe, explain and predict chemical structures, properties and reactions.

Links to Foundation to Year 10

The Chemistry curriculum continues to develop student understanding and skills from across the three strands of the F-10 Australian Curriculum: Science. In the Science Understanding strand, the Chemistry curriculum draws on knowledge and understanding from across the four sub-strands of Biological, Physical, Chemical and Earth and Space Sciences.

Representation of Cross-curriculum priorities

While the significance of the cross-curriculum priorities for Chemistry varies, there are opportunities for teachers to select contexts that incorporate the key concepts from each priority.

Achievement standards

Unit 1: Chemical fundamentals: structure, properties and reactions

Unit 1: Chemical fundamentals: structure, properties and reactions Description

Chemists design and produce a vast range of materials for many purposes, including for fuels, cosmetics, building materials and pharmaceuticals. As the science of chemistry has developed over time, there has been an increasing realisation that the properties of a material depend on, and can be explained by, the material’s structure. A range of models at the atomic and molecular scale enable explanation and prediction of the structure of materials and how this structure influences properties and reactions. In this unit, students relate matter and energy in chemical reactions, as they consider the breaking and reforming of bonds as new substances are produced. Students can use materials that they encounter in their lives as a context for investigating the relationships between structure and properties.

Through the investigation of appropriate contexts, students explore how evidence from multiple disciplines and individuals and the development of ICT and other technologies have contributed to developing understanding of atomic structure and chemical bonding. They explore how scientific knowledge is used to offer reliable explanations and predictions, and the ways in which it interacts with social, economic, cultural and ethical factors.

Students use science inquiry skills to develop their understanding of patterns in the properties and composition of materials. They investigate the structure of materials by describing physical and chemical properties at the macroscopic scale, and use models of structure and primary bonding at the atomic and sub-atomic scale to explain these properties. They are introduced to the mole concept as a means of quantifying matter in chemical reactions.

Unit 1: Chemical fundamentals: structure, properties and reactions Learning Outcomes

By the end of this unit, students:

understand how the atomic model and models of bonding explain the structure and properties of elements and compounds
understand the concept of enthalpy, and apply this to qualitatively and quantitatively describe and explain energy changes in chemical reactions
understand how models and theories have developed based on evidence from a range of sources, and the uses and limitations of chemical knowledge in a range of contexts
use science inquiry skills to design, conduct, evaluate and communicate investigations into the properties of elements, compounds and mixtures and the energy changes involved in chemical reactions
evaluate, with reference to empirical evidence, claims about chemical properties, structures and reactions
communicate, predict and explain chemical phenomena using qualitative and quantitative representations in appropriate modes and genres.

Unit 1: Chemical fundamentals: structure, properties and reactions Content Descriptions

Science Inquiry Skills (Chemistry Unit 1)

Identify, research and refine questions for investigation; propose hypotheses; and predict possible outcomes (ACSCH001)

Design investigations, including the procedure/s to be followed, the materials required, and the type and amount of primary and/or secondary data to be collected; conduct risk assessments; and consider research ethics (ACSCH002)

Conduct investigations, including the use of devices to accurately measure temperature change and mass, safely, competently and methodically for the collection of valid and reliable data (ACSCH003)

Represent data in meaningful and useful ways, including using appropriate graphic representations and correct units and symbols; organise and process data to identify trends, patterns and relationships; identify sources of random and systematic error and estimate their effect on measurement results; and select, synthesise and use evidence to make and justify conclusions (ACSCH004)

Interpret a range of scientific and media texts, and evaluate processes, claims and conclusions by considering the quality of available evidence; and use reasoning to construct scientific arguments (ACSCH005)

Select, construct and use appropriate representations including chemical symbols and formulae, molecular structural formulae, physical and graphical models of structures, chemical equations and thermochemical equations, to communicate conceptual understanding, solve problems and make predictions (ACSCH006)

Select and use appropriate mathematical representations to solve problems and make predictions, including calculating percentage composition from relative atomic masses and using the mole concept to calculate the mass of reactants and products (ACSCH007)

Communicate to specific audiences and for specific purposes using appropriate language, nomenclature, genres and modes, including scientific report (ACSCH008)

Science as a Human Endeavour (Units 1 and 2)

Science is a global enterprise that relies on clear communication, international conventions, peer review and reproducibility (ACSCH009)

Development of complex models and/or theories often requires a wide range of evidence from multiple individuals and across disciplines (ACSCH010)

Advances in science understanding in one field can influence other areas of science, technology and engineering (ACSCH011)

The use of scientific knowledge is influenced by social, economic, cultural and ethical considerations (ACSCH012)

The use of scientific knowledge may have beneficial and/or harmful and/or unintended consequences (ACSCH013)

Scientific knowledge can enable scientists to offer valid explanations and make reliable predictions (ACSCH014)

Scientific knowledge can be used to develop and evaluate projected economic, social and environmental impacts and to design action for sustainability (ACSCH015)

Science Understanding

Properties and structure of atoms

Examples in context

Support materials only that illustrate some possible contexts for exploring Science as a Human Endeavour concepts in relation to Science Understanding content.

Models of the atom

In the early nineteenth century, Dalton proposed some fundamental properties of atoms that would explain existing laws of chemistry. One century later, a range of experiments provided evidence that enabled scientists to develop models of the structure of the atom. These included using radiation in the form of X-rays and alpha particles, and the passing of particles through a magnetic field to determine their mass (ACSCH010). Evidence from French physicist Becquerel’s discovery of radioactivity suggested the presence of subatomic particles, and this was also a conclusion from gas discharge experiments. British physicist J.J. Thomson was able to detect electrons, and his results, combined with the later work of Millikan, an American experimental physicist, resulted in both the charge and mass of electrons being calculated (ACSCH009). The British chemist Rutherford proposed a model of the atom comprising a heavy nucleus surrounded by space in which electrons were found, and Danish physicist Bohr’s model further described how these electrons existed in distinct energy levels. The last of the main subatomic particles, the neutron, was discovered by the English physicist Chadwick in 1932, by bombarding samples of boron with alpha particles from radioactive polonium (ACSCH010).

Radioisotopes

Radioisotopes have a wide variety of uses, including Carbon-14 for carbon dating in geology and palaeobiology; radioactive tracers such as Iodine-131 in nuclear medicine; radioimmuno-assays for testing constituents of blood, serum, urine, hormones and antigens; and radiotherapy that destroys damaged cells (ACSCH011). Use of radioisotopes requires careful evaluation and monitoring because of the potential harmful effects to humans and/or the environment if their production, use and disposal are not managed effectively (ACSCH013). Risks include unwanted damage to cells in the body, especially during pregnancy, and ongoing radiation produced from radioactive sources with long half-lives.

Distribution of elements in the universe

Analysis of the distribution of elements in living things, Earth and the universe has informed a wide range of scientific understandings, including the role of calcium exclusion from bacteria in the evolution of shells and bones; the proliferation of carbon (rather than silicon, which has similar properties and is more abundant in Earth’s crust) in living things; the elemental composition of historical artefacts; and the origin of elements through nuclear fusion in stars (ACSCH011). Analysis of element distribution is informed by data from spectral analysis and other technologies. Evidence from these techniques enables scientists to draw conclusions about a range of phenomena, such as the chemical changes involved in natural processes in both biological and cosmological systems, and the geographic source of historical artefacts (ACSCH014).

Trends in the observable properties of elements are evident in periods and groups in the periodic table (ACSCH016)

The structure of the periodic table is based on the electron configuration of atoms, and shows trends, including in atomic radii and valencies (ACSCH017)

Atoms can be modelled as a nucleus surrounded by electrons in distinct energy levels, held together by electrostatic forces of attraction between the nucleus and electrons; atoms can be represented using electron shell diagrams (all electron shells or valence shell only) or electron charge clouds (ACSCH018)

Flame tests and atomic absorption spectroscopy are analytical techniques that can be used to identify elements; these methods rely on electron transfer between atomic energy levels (ACSCH019)

The properties of atoms, including their ability to form chemical bonds, are explained by the arrangement of electrons in the atom and in particular by the stability of the valence electron shell (ACSCH020)

Isotopes are atoms of an element with the same number of protons but different numbers of neutrons; different isotopes of elements are represented using atomic symbols (for example, \({}_6^{12}C\), \({}_6^{13}C\) (ACSCH021)

Isotopes of an element have the same electron configuration and possess similar chemical properties but have different physical properties, including variations in nuclear stability (ACSCH022)

Mass spectrometry involves the ionisation of substances and generates spectra which can be analysed to determine the isotopic composition of elements (ACSCH023)

The relative atomic mass of an element is the ratio of the weighted average mass per atom of the naturally occurring form of the element to \(\frac1{12}\) the mass of an atom of carbon-12; relative atomic masses reflect the isotopic composition of the element (ACSCH024)

Properties and structure of materials

Examples in context

Support materials only that illustrate some possible contexts for exploring Science as a Human Endeavour concepts in relation to Science Understanding content.

Nanomaterials

Development of organic and inorganic nanomaterials is increasingly important to meet a range of contemporary needs, including consumer products, health care, transportation, energy and agriculture (ACSCH013). Nanomaterials have special physical and chemical properties that make them useful for environmentally friendly products, such as more durable materials, dirt- and water-repellent coatings designed to help reduce cleaning efforts, and insulating materials that improve the energy efficiency of buildings (ACSCH015). Although there are many projected environmental benefits, there are also potential risks associated with the use of nanomaterials due to the size of the particles involved (for example, some are able to cross the human blood-brain or placental barrier) and the unknown effects of these particles on human health and the environment (ACSCH013).

The importance of purity

There is a large range of situations in chemistry where knowing and communicating the level of purity of substances is extremely important. Impurities can affect the physical and chemical properties of substances, resulting in inefficient or unwanted chemical reactions. Scientists use methods such as mass spectrometry to identify impurities and the level of contamination (ACSCH014). Separation methods which improve the purity of substances are used for food, fuels, cosmetics, medical products and metals used in microelectronic devices. Scientific conventions and international standards are used to represent the purity of materials to ensure consistent applications of standards (ACSCH009).

Carbon based life and astrobiology

Carbon is far more prevalent in living organisms than silicon, even though silicon is more abundant than carbon in Earth’s crust. This has caused some scientists to question why life on Earth has evolved to be carbon-based. Although carbon and silicon are found in the same group of the periodic table and share similar characteristics, carbon has a range of properties that mean there is more variety in its interactions and the molecules it can form, which is pivotal to biochemical molecules such as carbohydrates, proteins and DNA. These properties of carbon, in addition to analysis of elements found in meteorites, comets and interstellar clouds, cause many astrobiologists to theorise that if life exists elsewhere in the universe, it will be carbon-based as it is on Earth (ACSCH010). Astrobiology, which is concerned with the distribution of life in our own and other solar systems, is a highly interdisciplinary field that draws on the findings of a range of scientists from areas such as geology, molecular biology, astronomy and chemistry (ACSCH011).

Materials are either pure substances with distinct measurable properties (for example, melting and boiling point, reactivity, strength, density) or mixtures with properties dependent on the identity and relative amounts of the substances that make up the mixture (ACSCH025)

Differences in the properties of substances in a mixture, such as particle size, solubility, magnetism, density, electrostatic attraction, melting point and boiling point, can be used to separate them (ACSCH026)

The type of bonding within substances explains their physical properties, including melting and boiling point, conductivity of both electricity and heat, strength and hardness (ACSCH027)

Nanomaterials are substances that contain particles in the size range 1–100 nm and have specific properties relating to the size of these particles (ACSCH028)

Chemical bonds are caused by electrostatic attractions that arise because of the sharing or transfer of electrons between participating atoms; the valency is a measure of the number of bonds that an atom can form (ACSCH029)

Ions are atoms or groups of atoms that are electrically charged due to an imbalance in the number of electrons and protons; ions are represented by formulae which include the number of constituent atoms and the charge of the ion (for example, O²^–, SO₄^2–) (ACSCH030)

The properties of ionic compounds (for example, high melting point, brittleness, ability to conduct electricity when liquid or in solution) are explained by modelling ionic bonding as ions arranged in a crystalline lattice structure with forces of attraction between oppositely charged ions (ACSCH031)

The characteristic properties of metals (for example, malleability, thermal conductivity, electrical conductivity) are explained by modelling metallic bonding as a regular arrangement of positive ions (cations) made stable by electrostatic forces of attraction between these ions and the electrons that are free to move within the structure (ACSCH032)

Covalent substances are modelled as molecules or covalent networks that comprise atoms which share electrons, resulting in electrostatic forces of attraction between electrons and the nucleus of more than one atom (ACSCH033)

Elemental carbon exists as a range of allotropes, including graphite, diamond and fullerenes, with significantly different structures and physical properties (ACSCH034)

Carbon forms hydrocarbon compounds, including alkanes and alkenes, with different chemical properties that are influenced by the nature of the bonding within the molecules (ACSCH035)

Chemical reactions: reactants, products and energy change

Examples in context

Support materials only that illustrate some possible contexts for exploring Science as a Human Endeavour concepts in relation to Science Understanding content.

Minimising use of energy in industry

Industries are encouraged to reduce their energy requirements in order to save money and reduce greenhouse gas emissions. One of the roles of chemical engineers is to consider the environmental, safety and economic aspects of energy use in the production of chemicals and to design and monitor chemical processes (ACSCH015). Green chemistry principles can be applied to industrial processes to reduce energy requirements; examples of these include recycling heat energy in chemical processes to improve efficiency and reduce cost and environmental impact, and redesigning chemical manufacturing processes to use less energy (ACSCH013).

Energy in the body

Our bodies rely on the exothermic reaction of respiration to provide us with sufficient energy. Metabolism involves using the energy provided by carbohydrates, proteins and fats in our diet. Typically, food energy is determined based on heats of combustion in a bomb calorimeter, enabling foods to be compared based on the amount of energy they contain (ACSCH011). This information is provided as part of the requirements for processed food labelling in many countries to help consumers control their energy intake. In some instances this information is expressed as a proportion of daily average energy requirements, typically using a value ranging from 7500 to 8700 kJ (ACSCH012). However each individual’s body energy requirements varies depending on their gender, age, mode of activity and the environmental conditions they live in, so an average value may provide limited guidance.

Use of fuels in society

A significant majority of the energy used for production of electricity, transport and household heating is sourced through the combustion of fuels. Fuels, including fossil fuels and biofuels, can be compared in terms of efficiency and environmental impact, for example by calculating the amount of carbon emissions produced per tonne of fuel used (ACSCH015). Decisions about which fuels to use can reflect social, economic, cultural and political values associated with the source of the fuel. For example, cultural values might inform the use of wood for heating houses; economic and social values might inform the use of crops for biofuel production instead of food production; and economic, social and political values might inform the use of brown coal rather than black coal, despite its being considered a low grade fuel (ACSCH012).

All chemical reactions involve the creation of new substances and associated energy transformations, commonly observable as changes in the temperature of the surroundings and/or the emission of light (ACSCH036)

Endothermic and exothermic reactions can be explained in terms of the Law of Conservation of Energy and the breaking and reforming of bonds; heat energy released or absorbed can be represented in thermochemical equations (ACSCH037)

Fuels, including fossil fuels and biofuels, can be compared in terms of their energy output, suitability for purpose, and the nature of products of combustion (ACSCH038)

A mole is a precisely defined quantity of matter equal to Avogadro’s number of particles; the mole concept and the Law of Conservation of Mass can be used to calculate the mass of reactants and products in a chemical reaction (ACSCH039)

Unit 2: Molecular interactions and reactions

Unit 2: Molecular interactions and reactions Description

In this unit, students develop their understanding of the physical and chemical properties of materials including gases, water and aqueous solutions, acids and bases. Students explore the characteristic properties of water that make it essential for physical, chemical and biological processes on Earth, including the properties of aqueous solutions. They investigate and explain the solubility of substances in water, and compare and analyse a range of solutions. They learn how rates of reaction can be measured and altered to meet particular needs, and use models of energy transfer and the structure of matter to explain and predict changes to rates of reaction. Students gain an understanding of how to control the rates of chemical reactions, including through the use of a range of catalysts.

Through the investigation of appropriate contexts, students explore how evidence from multiple disciplines and individuals and the development of ICT and other technologies have contributed to developing understanding of intermolecular forces and chemical reactions. They explore how scientific knowledge is used to offer reliable explanations and predictions, and the ways in which it interacts with social, economic, cultural and ethical factors.

Students use a range of practical and research inquiry skills to investigate chemical reactions, including the prediction and identification of products and the measurement of the rate of reaction. They investigate the behaviour of gases, and use the kinetic theory to predict the effects of changing temperature, volume and pressure in gaseous systems.

Unit 2: Molecular interactions and reactions Learning Outcomes

By the end of this unit, students:

understand how models of the shape and structure of molecules and intermolecular forces can be used to explain the properties of substances, including the solubility of substances in water
understand how kinetic theory can be used to explain the behaviour of gaseous systems, and how collision theory can be used to explain and predict the effect of varying conditions on the rate of reaction
understand how models and theories have developed based on evidence from multiple disciplines, and the uses and limitations of chemical knowledge in a range of contexts
use science inquiry skills to design, conduct, evaluate and communicate investigations into the properties and behaviour of gases, water, aqueous solutions and acids and the factors that affect the rate of chemical reactions
evaluate, with reference to empirical evidence, claims about chemical properties, structures and reactions
communicate, predict and explain chemical phenomena using qualitative and quantitative representations in appropriate modes and genres.

Unit 2: Molecular interactions and reactions Content Descriptions

Science Inquiry Skills (Chemistry Unit 2)

Identify, research, construct and refine questions for investigation; propose hypotheses; and predict possible outcomes (ACSCH040)

Conduct investigations, including measuring pH and the rate of formation of products, identifying the products of reactions, and testing solubilities, safely, competently and methodically for the collection of valid and reliable data (ACSCH042)

Represent data in meaningful and useful ways, including using appropriate graphic representations and correct units and symbols; organise and process data to identify trends, patterns and relationships; identify sources of random and systematic error; identify anomalous data; estimate the effect of error on measured results; and select, synthesise and use evidence to make and justify conclusions (ACSCH043)

Select, construct and use appropriate representations, including physical and graphical models of molecules, energy profile diagrams, electron dot diagrams, ionic formulae, chemical formulae, chemical equations and phase descriptors for chemical species to communicate conceptual understanding, solve problems and make predictions (ACSCH045)

Select and use appropriate mathematical representations to solve problems and make predictions, including using the mole concept to calculate the mass of chemicals and/or volume of a gas (at standard temperature and pressure) involved in a chemical reaction, and using the relationship between the number of moles of solute, concentration and volume of a solution to calculate unknown values (ACSCH046)

Communicate to specific audiences and for specific purposes using appropriate language, nomenclature, genres and modes, including scientific reports (ACSCH047)

Science as a Human Endeavour (Units 1 and 2)

Science is a global enterprise that relies on clear communication, international conventions, peer review, and reproducibility (ACSCH048)

Development of complex models and/or theories often requires a wide range of evidence from multiple individuals and across disciplines (ACSCH049)

Advances in science understanding in one field can influence other areas of science, technology and engineering (ACSCH050)

The use of scientific knowledge is influenced by social, economic, cultural and ethical considerations (ACSCH051)

The use of scientific knowledge may have beneficial and/or harmful and/or unintended consequences (ACSCH052)

Scientific knowledge can enable scientists to offer valid explanations and make reliable predictions (ACSCH053)

Scientific knowledge can be used to develop and evaluate projected economic, social and environmental impacts and to design action for sustainability (ACSCH054)

Science Understanding

Intermolecular forces and gases

Examples in context

Support materials only that illustrate some possible contexts for exploring Science as a Human Endeavour concepts in relation to Science Understanding content.

Analysing the structure of materials – forensic chemistry

Forensic science often relies on chemical processes to analyse materials in order to determine the identity, nature or source of the material (ACSCH052). This requires detailed knowledge of both chemical and physical properties of a range of substances as well as the structure of the materials. Analysis techniques include different forms of chromatography to determine the components of a mixture, for example analysis of urine samples to identify drugs or drug byproducts, identification of traces of explosives, or the presence of an unusual substance at a crime scene. Evidence from forensic analysis can be used to explain the nature and source of samples and predict events based on the combination of evidence from a range of sources (ACSCH053). Calculations of quantities, including the concentrations of solutions, are an essential part of forensic chemistry, as is consideration of the reliability of evidence and the accuracy of forensic tests.

Scuba diving and the behaviour of gases

Safe scuba diving requires knowledge of the behaviour of gases with reference to volume, pressure and temperature. In particular, divers should understand how the volume of a gas varies with the surrounding pressure, in order to prevent damage to their respiratory, circulatory and nervous system. Diving equipment is designed to reduce the risk of dealing with gases at high pressure, including both the choice of materials used and the design of systems to improve efficiency and safety (ACSCH052). Guidelines and regulations based on understanding of gas compression and expansion due to changes in water pressure enable divers to avoid conditions such as pulmonary barotrauma and decompression sickness (ACSCH053).

Development of VSEPR theory

Valence Shell Electron Pair Repulsion (VSEPR) theory is based on an understanding of subatomic and molecular structure and is an extremely powerful tool in the prediction of the shapes of molecules. In 1940 Sidgwick and Powell proposed that the shapes of molecules are dependent on the number of valence electrons in atoms within molecules. This idea was developed further by Australian scientist Sydney Nyholm and Canadian Ronald Gillespie in 1957 to describe how electrostatic repulsion between bonding and/or non-bonding pairs of electrons can be used to reliably predict the shapes of molecules (ACSCH049). They were able to demonstrate a relationship between the internal electronic structure of molecules, as predicted by knowledge of chemical bonding, and the overall shape of the molecules, as revealed by methods such as and X-ray crystallography (ACSCH048). Two- and three-dimensional graphical models have been developed and adopted by chemists to represent and communicate the shapes of molecules (ACSCH048).

Observable properties, including vapour pressure, melting point, boiling point and solubility, can be explained by considering the nature and strength of intermolecular forces within a substance (ACSCH055)

The shapes of molecules can be explained and predicted using three-dimensional representations of electrons as charge clouds and using valence shell electron pair repulsion (VSEPR) theory (ACSCH056)

The polarity of molecules can be explained and predicted using knowledge of molecular shape, understanding of symmetry, and comparison of the electronegativity of elements (ACSCH057)

The shape and polarity of molecules can be used to explain and predict the nature and strength of intermolecular forces, including dispersion forces, dipole-dipole forces and hydrogen bonding (ACSCH058)

Data from chromatography techniques (for example, thin layer, gas and high-performance liquid chromatography) can be used to determine the composition and purity of substances; the separation of the components is caused by the variation of strength of the interactions between atoms, molecules or ions in the mobile and stationary phases (ACSCH059)

The behaviour of gases, including the qualitative relationships between pressure, temperature and volume, can be explained using kinetic theory (ACSCH060)

Aqueous solutions and acidity

Examples in context

Support materials only that illustrate some possible contexts for exploring Science as a Human Endeavour concepts in relation to Science Understanding content.

Acid rain

Rain water is naturally acidic as a result of carbon dioxide dissolved in water and from volcanic emission of sulphur. However scientists have observed an ongoing increase in the acidity of rain and the reduction of the pH of the oceans, which has been explained by an increased release of acidic gases including carbon dioxide, nitrogen oxides and sulphur dioxide into the atmosphere (ACSCH053). Most sulphur dioxide released to the atmosphere comes from burning coal or oil in electric power stations. Scientists have used trends in data to predict that continued increases in acidic emissions will have adverse effects on aquatic systems, forests, soils, buildings, cultural objects and human health (ACSCH053). Concern over acid rain has led to the design of technical solutions such as flue-gas desulphurisation (FGD) to remove sulphur-containing gases from coal-fired power station stacks, and emissions controls such as exhaust gas recirculation to reduce nitrogen oxide emissions from vehicles (ACSCH054). A number of international treaties and emissions trading schemes also seek to lower acidic emissions.

Blood chemistry

Blood plasma is an aqueous solution containing a range of ionic and molecular substances. Maintenance of normal blood solute concentrations and pH levels is vital for our health. Changes in blood chemistry can be indicative of a range of conditions such as diabetes, which is indicated by changed sugar levels. Pathologists compare sample blood plasma concentrations to reference ranges that reflect the normal values found in the population and analyse variations to infer presence of disease (ACSCH050). Knowledge of blood solute concentration is used to design intravenous fluids at appropriate concentrations, and to design plasma expanders such as solutions of salts for treatment of severe blood loss (ACSCH052).

Water quality

The issue of security of drinking water supplies is extremely important in Australia and many parts of the Asia region. Scientists have developed regulations for safe levels of solutes in drinking water and chemists use a range of methods to monitor water supplies to ensure that these levels are adhered to. Water from different sources has differing ionic concentrations, for example, bore water has a high iron content. Knowledge of the composition of water from different sources informs decisions about how that water is treated and used (ACSCH052). Desalination plants have been built around Australia to meet the supply needs of drinking water. These have high energy requirements and can have unwanted environmental impacts where the water is extracted from the oceans. Scientific knowledge and experimental evidence informs international action aimed at addressing current and future issues around the supply of potable water (ACSCH054).

Water is a key substance in a range of chemical systems because of its unique properties, including its boiling point, density in solid and liquid phases, surface tension, and ability to act as a solvent (ACSCH061)

The unique properties of water can be explained by its molecular shape and hydrogen bonding between molecules (ACSCH062)

The concentration of a solution is defined as the amount of solute divided by the amount of solution; this can be represented in a variety of ways including by the number of moles of the solute per litre of solution (mol L^-1) and the mass of the solute per litre of solution (g L^-1) (ACSCH063)

The presence of specific ions in solutions can be identified using analytical techniques based on chemical reactions, including precipitation and acid-base reactions (ACSCH064)

The solubility of substances in water, including ionic and molecular substances, can be explained by the intermolecular forces between species in the substances and water molecules, and is affected by changes in temperature (ACSCH065)

The pH scale is used to compare the levels of acidity or alkalinity of aqueous solutions; the pH is dependent on the concentration of hydrogen ions in the solution (ACSCH066)

Patterns of the reactions of acids and bases (for example, reactions of acids with bases, metals and carbonates) allow products to be predicted from known reactants (ACSCH067)

Rates of chemical reactions

Examples in context

Support materials only that illustrate some possible contexts for exploring Science as a Human Endeavour concepts in relation to Science Understanding content.

The importance of enzymes

Enzymes are specific to particular reactions and act as important catalysts in many biological reactions, including those involved in digestion and respiration. Evidence for the existence and action of enzymes initially arose from Louis Pasteur’s study of fermentation of sugar to form alcohol in the nineteenth century. Further work, involving a wide range of scientists, proposed that enzyme action was associated with protein molecules (ACSCH049). Catalysts work in a variety of ways, and knowledge of the structure of enzyme molecules helps scientists to explain and predict how they are able to lower the activation energy for reactions (ACSCH053). This work often relies on evidence from laboratory experiments as well as analytical methods used to determine the structure of molecules (ACSCH049). For example, Australian John Cornforth was awarded the Nobel Prize for chemistry for his study of the molecular geometry of enzymes and how they are able to catalyse essential biochemical reactions.

Cost of corrosion

Corrosion of metals can have significant negative economic, environmental and safety consequences. For example, corrosion of steel pipes led to the 2008 gas plant explosion on Varunus Island, Western Australia, cutting the state’s gas supply by 30%. Many heritage structures, particularly bridges, have significant corrosion issues that compromise user safety, such as corrosion of main cables on suspension bridges. Addressing these issues can be complex and costly, and decisions about maintenance or replacement often involve consideration of factors such as cost, aesthetic or cultural value, and safety (ACSCH052). Most contemporary methods of corrosion prevention rely on knowledge of chemical and electrochemical redox processes, including the use of graphene within varnish coatings of iron or steel. The extension of a metal’s useful life will achieve cost savings and improve environmental impacts for many Australian industries, where a significant amount of industry is located on the coast and/or relies on shipping for imports and exports (ACSCH054).

Development of collision theory

Collision theory enables chemists to explain and predict the rates of a vast range of chemical reactions in many different contexts (ACSCH053). German chemist Max Trautz published research about aspects of collision theory, in particular the significance of activation energy, in 1916. William Lewis, working independently in England at the same time, proposed complimentary work on collision theory in 1918 (ACSCH048). The First World War prevented not only the two chemists working together, but even being aware of each other’s work. Further work on collision theory enabled a quantitative approach to be taken which allowed for the prediction and control of chemical reaction rates; these understandings are now used by chemical engineers to design efficient, safe and economically viable industrial processes (ACSCH052).

Varying the conditions present during chemical reactions can affect the rate of the reaction and in some cases the identity of the products (ACSCH068)

The rate of chemical reactions can be quantified by measuring the rate of formation of products or the depletion of reactants (ACSCH069)

Collision theory can be used to explain and predict the effect of concentration, temperature, pressure and surface area on the rate of chemical reactions by considering the structure of the reactants and the energy of particles (ACSCH070)

The activation energy is the minimum energy required for a chemical reaction to occur and is related to the strength of the existing chemical bonds; the magnitude of the activation energy influences the rate of a chemical reaction (ACSCH071)

Energy profile diagrams can be used to represent the enthalpy changes and activation energy associated with a chemical reaction (ACSCH072)

Catalysts, including enzymes and metal nanoparticles, affect the rate of certain reactions by providing an alternative reaction pathway with a reduced activation energy, hence increasing the proportion of collisions that lead to a chemical change (ACSCH073)

Unit 3: Equilibrium, acids and redox reactions

Unit 3: Equilibrium, acids and redox reactions Description

The idea of reversibility of reaction is vital in a variety of chemical systems at different scales, ranging from the processes that release carbon dioxide into our atmosphere to the reactions of ions within individual cells in our bodies. Processes that are reversible will respond to a range of factors and can achieve a state of dynamic equilibrium. In this unit, students investigate acid-base equilibrium systems and their applications. They use contemporary models to explain the nature of acids and bases, and their properties and uses. This understanding enables further exploration of the varying strengths of acids and bases. Students investigate the principles of oxidation and reduction reactions and the production of electricity from electrochemical cells.

Through the investigation of appropriate contexts, students explore the ways in which models and theories related to acid-base and redox reactions, and their applications, have developed over time and through interactions with social, economic, cultural and ethical considerations. They explore the ways in which chemistry contributes to contemporary debate in industrial and environmental contexts, including the use of energy, evaluation of risk and action for sustainability, and they recognise the limitations of science in providing definitive answers in different contexts.

Students use science inquiry skills to investigate the principles of dynamic chemical equilibrium and how these can be applied to chemical processes and systems. They investigate a range of electrochemical cells, including the choice of materials used and the voltage produced by these cells. Students use the pH scale to assist in making judgements and predictions about the extent of dissociation of acids and bases and about the concentrations of ions in an aqueous solution.

Unit 3: Equilibrium, acids and redox reactions Learning Outcomes

By the end of this unit, students:

understand the characteristics of equilibrium systems, and explain and predict how they are affected by changes to temperature, concentration and pressure
understand the difference between the strength and concentration of acids, and relate this to the principles of chemical equilibrium
understand how redox reactions, galvanic and electrolytic cells are modelled in terms of electron transfer
understand how models and theories have developed over time and the ways in which chemical knowledge interacts with social, economic, cultural and political considerations in a range of contexts
use science inquiry skills to design, conduct, evaluate and communicate investigations into the properties of acids and bases, redox reactions and electrochemical cells, including volumetric analysis
evaluate, with reference to empirical evidence, claims about equilibrium systems and justify evaluations
communicate, predict and explain chemical phenomena using qualitative and quantitative representations in appropriate modes and genres.

Unit 3: Equilibrium, acids and redox reactions Content Descriptions

Science Inquiry Skills (Chemistry Unit 3)

Identify, research, construct and refine questions for investigation; propose hypotheses; and predict possible outcomes (ACSCH074)

Conduct investigations, including using volumetric analysis techniques and constructing electrochemical cells, safely, competently and methodically for the collection of valid and reliable data (ACSCH076)

Represent data in meaningful and useful ways, including using appropriate graphic representations and correct units and symbols; organise and process data to identify trends, patterns and relationships; identify and distinguish between random and systematic errors, and estimate their effect on measured results; discuss how the nature of the procedure and the sample size may influence uncertainty and limitations in data; and select, synthesise and use evidence to make and justify conclusions (ACSCH077)

Interpret a range of scientific texts, and evaluate processes, claims and conclusions by considering the quality of available evidence, including confidence intervals in secondary data; and use reasoning to construct scientific arguments (ACSCH078)

Select, construct and use appropriate representations, including half-equations, balanced chemical equations, equilibrium constants and expressions, pH, oxidation numbers, standard electrode potentials and cell diagrams, to communicate conceptual understanding, solve problems and make predictions (ACSCH079)

Select and use appropriate mathematical representations to solve problems and make predictions, including calculating cell potentials under standard conditions, using the mole concept to calculate moles, mass, volume and concentrations from volumetric analysis data, determining the yield of incomplete reactions, and calculating the pH of solutions of strong acids and bases (ACSCH080)

Communicate to specific audiences and for specific purposes using appropriate language, nomenclature, genres and modes, including scientific reports (ACSCH081)

Science as a Human Endeavour (Units 3 & 4)

ICT and other technologies have dramatically increased the size, accuracy and geographic and temporal scope of data sets with which scientists work (ACSCH082)

Models and theories are contested and refined or replaced when new evidence challenges them, or when a new model or theory has greater explanatory power (ACSCH083)

The acceptance of scientific knowledge can be influenced by the social, economic, and cultural context in which it is considered (ACSCH084)

People can use scientific knowledge to inform the monitoring, assessment and evaluation of risk (ACSCH085)

Science can be limited in its ability to provide definitive answers to public debate; there may be insufficient reliable data available, or interpretation of the data may be open to question (ACSCH086)

International collaboration is often required when investing in large-scale science projects or addressing issues for the Asia-Pacific region (ACSCH087)

Scientific knowledge can be used to develop and evaluate projected economic, social and environmental impacts and to design action for sustainability (ACSCH088)

Science Understanding

Chemical equilibrium systems

Examples in context

Support materials only that illustrate some possible contexts for exploring Science as a Human Endeavour concepts in relation to Science Understanding content.

Chemical balance in wine

The production of wine, along with that of many other food products, relies on the successful control of a range of reversible reactions in order to maintain the required chemical balance within the product. For wine, this balance includes the acidity, alcohol concentration, sugar levels and the colour of the wine. Techniques such as auto titration, gas chromatography and infrared spectroscopy are used to measure the chemical composition of wine. Data from these methods, including the analysis of multivariate data, has enabled scientists to identify how the concentrations of the various chemicals in the wine are related, both to each other and the observable properties of wine such as taste and aroma (ACSCH082). Sulphur dioxide is used to maintain chemical balance in wine, as it binds with acetaldehyde. ‘Sulphite calculators’ are available so that wine makers can predict the amount of sulphur dioxide required. However decisions as to how the sulphur dioxide is added to the wine, including how much to use, will depend on preferences of the winemaker, especially for those producers who market wine as ‘organic’ or ‘preservative free’ (ACSCH084).

Carbon dioxide in the atmosphere and hydrosphere

The levels of carbon dioxide in the atmosphere have a significant influence on global systems, including surface temperatures. The oceans contribute to the maintenance of steady concentrations of atmospheric carbon dioxide because the gas can dissolve in seawater through a range of reversible processes. The uptake of anthropogenic carbon dioxide by the oceans is driven by the difference in gas pressure in the atmosphere and in the oceans, and by the air/sea transfer velocity. Because carbon dioxide is increasing in the atmosphere, more of it moves into the ocean to balance the oceanic and atmospheric gas pressures, causing a change in the equilibrium point. Dissolved carbon dioxide increases ocean acidity, which is predicted to have a range of negative consequences for ecosystems, including direct impacts on oceanic calcifying organisms such as corals, crustaceans and molluscs because structures made of calcium carbonate are vulnerable to dissolution under at lower pH levels (ACSCH088). The United Nations Kyoto Protocol and the establishment of the Intergovernmental Panel on Climate Change aim to secure global commitment to a significant reduction in greenhouse gas emissions over the next decades (ACSCH087).

Development of acid/base models

Lavoisier, often referred to as the father of modern chemistry, believed that all acids contained oxygen. In 1810, Davy proposed that it was hydrogen, rather than oxygen, that was common to all acids (ACSCH083). Arrhenius linked the behaviour of acids to their ability to produce hydrogen ions in aqueous solution, however this theory only related to aqueous solutions and relied on all bases producing hydroxide ions. In 1923 Brønsted (and at about the same time, Lowry) refined the earlier theories by describing acids as proton donators (ACSCH083). This theory allowed for the description of conjugate acid-bases, and for the explanation of the varying strength of acids based on the stability of the ions produced when acids ionise to form the hydrogen ions. This concept has been applied to contemporary research into ‘superacids’, such as carborane acids, which have been found to be a million times stronger than sulphuric acid when the position of equilibrium in aqueous solution is considered.

Chemical systems may be open or closed and include physical changes and chemical reactions which can result in observable changes to the system (ACSCH089)

All physical changes are reversible, whereas only some chemical reactions are reversible (ACSCH090)

Over time, physical changes and reversible chemical reactions reach a state of dynamic equilibrium in a closed system, with the relative concentrations of products and reactants defining the position of equilibrium (ACSCH091)

The reversibility of chemical reactions can be explained by considering the activation energies of the forward and reverse reactions (ACSCH092)

The effect of changes of temperature on chemical systems at equilibrium can be explained by considering the enthalpy changes for the forward and reverse reactions (ACSCH093)

The effect of changes of concentration and pressure on chemical systems at equilibrium can be explained and predicted by applying collision theory to the forward and reverse reactions (ACSCH094)

The effects of changes of temperature, concentration of chemicals and pressure on equilibrium systems can be predicted using Le Chatelier’s Principle (ACSCH095)

Equilibrium position can be predicted qualitatively using equilibrium constants (ACSCH096)

Acids are substances that can act as proton (hydrogen ion) donors and can be classified as monoprotic or polyprotic depending on the number of protons donated by each molecule of the acid (ACSCH097)

The strength of acids is explained by the degree of ionisation at equilibrium in aqueous solution, which can be represented with chemical equations and equilibrium constants (Ka) (ACSCH098)

The relationship between acids and bases in equilibrium systems can be explained using the Brønsted-Lowry model and represented using chemical equations that illustrate the transfer of hydrogen ions (ACSCH099)

The pH scale is a logarithmic scale and the pH of a solution can be calculated from the concentration of hydrogen ions; K_w can be used to calculate the concentration of hydrogen ions from the concentration of hydroxide ions in a solution (ACSCH100)

Acid-base indicators are weak acids or bases where the acidic form is of a different colour to the basic form (ACSCH101)

Volumetric analysis methods involving acid-base reactions rely on the identification of an equivalence point by measuring the associated change in pH, using chemical indicators or pH meters, to reveal an observable end point (ACSCH102)

Oxidation and reduction

Examples in context

Support materials only that illustrate some possible contexts for exploring Science as a Human Endeavour concepts in relation to Science Understanding content.

Breathalysers and measurement of blood alcohol levels

The level of alcohol in the body can be measured by testing breath or blood alcohol concentrations (ACSCH085). These analysis techniques rely on redox reactions. Police first used breath testing for alcohol in the 1940s. Currently, a range of other detection methods are available to police, and commercially to drivers who are now able to test themselves before driving. Some meters use infrared spectroscopy to determine the amount of alcohol present, which can be converted to blood alcohol concentration (BAC). Electrochemical cells form the basis of ‘alcosensors’ which can also be used to measure BAC. These cells work by recording the electrical potential produced by the oxidation of the ethanol at platinum electrodes. Although science can provide information about the effect of alcohol on our bodies in relation to the ability to drive, decisions about ‘safe’ levels of BAC for driving (including those used to write legislation) take into account other factors, such as the experience of the driver, and can vary from country to country (ACSCH086).

Fuel cells and their uses

Redox reactions that occur spontaneously can be used as a source of electrical energy. These include wet cells (such as car batteries), dry cells, and alkaline batteries. Fuel cells are electrochemical cells that use up a ‘fuel’, such as hydrogen. Fuel cells were first demonstrated in the 1840s, but were not commercially available until the late twentieth century. Currently, small fuel cells are designed for laptop computers and other portable electronic devices; larger fuel cells are used to provide backup power for hospitals; and wastewater treatment plants and landfills make use of fuel cells to capture and convert the methane gas they produce into methane (ACSCH088). Fuel cells are a potential lower-emission alternative to the internal combustion engine and are already being used to power buses, boats, trains and cars (ACSCH088). International organisations such as the International Partnership for Hydrogen and Fuel Cells in the Economy (IPHE) have been created to foster international cooperation on research and development, common codes and standards, and information sharing on infrastructure development (ACSCH087).

Electrochemistry for clean water

Electrochemistry has a wide range of uses, ranging from industrial scale metal extraction to personal cosmetic treatments. A new application has been in the treatment of mineral rich bore water. New Zealand scientists have trialled a system that uses electrochemistry to remove the iron and manganese ions present in bore water, which currently make the water undrinkable. An electric current converts chloride ions to chlorine, which then oxidises and precipitates out the metal contaminants, as well as disinfecting the water. The electric current passing through the water also dramatically increased the effectiveness of the chlorine in killing organisms in the water. The process requires minimal current and can be provided by a 12-volt car battery, which makes it a cheap and relatively ‘low tech’ solution suitable for use in rural areas of developing countries (ACSCH087).

A range of reactions, including displacement reactions of metals, combustion, corrosion, and electrochemical processes, can be modelled as redox reactions involving oxidation of one substance and reduction of another substance (ACSCH103)

Oxidation can be modelled as the loss of electrons from a chemical species, and reduction can be modelled as the gain of electrons by a chemical species; these processes can be represented using half-equations (ACSCH104)

The ability of an atom to gain or lose electrons can be explained with reference to valence electrons, consideration of energy, and the overall stability of the atom, and can be predicted from the atom’s position in the periodic table (ACSCH105)

The relative strength of oxidising and reducing agents can be determined by comparing standard electrode potentials (ACSCH106)

Electrochemical cells, including galvanic and electrolytic cells, consist of oxidation and reduction half-reactions connected via an external circuit that allows electrons to move from the anode (oxidation reaction) to the cathode (reduction reaction) (ACSCH107)

Galvanic cells, including fuel cells, generate an electrical potential difference from a spontaneous redox reaction; they can be represented as cell diagrams including anode and cathode half-equations (ACSCH108)

Fuel cells can use metal nanoparticles as catalysts to improve the efficiency of energy production (ACSCH109)

Cell potentials at standard conditions can be calculated from standard electrode potentials; these values can be used to compare cells constructed from different materials (ACSCH110)

Electrolytic cells use an external electrical potential difference to provide the energy to allow a non-spontaneous redox reaction to occur, and can be used in small-scale and industrial situations (ACSCH111)