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Revision help links OCR GCSE 21st Century Combined Science chemistry C1-C3
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Revision summary help OCR GCSE 21st Century Combined Science B chemistry exam papers - learning objectives for exam paper on chapters C1, C2 and C3 chemistry F/H and combined science F/H papers for 2020 exams onwards OCR Level 1/2 GCSE (Grade 9-1) in Combined Science B Chemistry (Twenty First Century Science) (J260) - OCR 21st Century GCSE Grade 9-1 Combined Science B chemistry Chapter C1 "Air and water", Chapter C2 "Chemical patterns", Chapter C3 "Chemicals of the natural environment" for FT Chemistry paper 02, HT Chemistry Paper 06, FT Combined Science Paper 04, HT Combined Science Paper 08 LINK OCR 21st Century Combined Science chemistry chapters C4-C6 LINK for OCR 21st Century 9-1 GCSE CHEMISTRY B chapters C1-C3 LINK for OCR 21st Century 9-1 GCSE CHEMISTRY B chapters C4-C7 This is a BIG website, you need to take time to explore it [SEARCH BOX] Use your mobile phone or ipad etc. in 'landscape' orientation See also OCR Gateway Sciences A Revision HELP Links email doc brown - query? or comment? For ALL other exam papers, use and bookmark the link below PLEASE READ CAREFULLY THE FOLLOWING POINTS before using my OCR GCSE 21st Century science B pages
In OCR 9-1 GCSE Twenty First Century Combined Science B chemistry courses, note the following! Combined Science Paper 04/Paper 08 assesses the contents of ALL the chapters of biology, chemistry and physics! Syllabus-specification CONTENT INDEX of revision summary notes What's assessed in this paper? (OCR 9-1 GCSE Twenty First Century Combined Science B Chemistry) SUMMARY Chapter C1: Air and water (this page)
SUMMARY Chapter C2: Chemical patterns (this page)
SUMMARY Chapter C3: Chemicals of the natural environment (this page)
SUMMARY Chapter C4: Material choices (separate page)
SUMMARY Chapter C5: Chemical analysis (separate page)
SUMMARY Chapter C6: Making useful chemicals (separate page)
SUMMARY Chapter BCP7: Ideas about Science (separate page)
Note: Combined Science Paper 04 assesses the contents of ALL the chapters of biology, chemistry and physics! Key ideas in chemistry (for all papers) Chemistry is the science of the composition, structure, properties and reactions of matter, understood in terms of atoms, atomic particles and the way they are arranged and link together. It is concerned with the synthesis, formulation, analysis and characteristic properties of substances and materials of all kinds. You should be helped to appreciate the achievements of chemistry in showing how the complex and diverse phenomena of both the natural and man-made worlds can be described in terms of a small number of key ideas which are of universal application, and which include:
A page of important ideas, concepts and definitions for chemistry students Chapter C1: Air and water (Revision for OCR GCSE 91 Twenty First Century Science Combined Science B chemistry 02, Topics for Chapter C1 "Air and water") Overview of Chapter C1 Air and Water The quality of our air and water is a major world concern. Chemists monitor our air and water, and work to minimise the impact of human activities on their quality. In Topic C1.1, the context of changes in the Earths atmosphere is used to explore the particle model and its limitations when explaining changes of state, and the principles of balancing equations for combustion reactions. As a development of ideas about burning fuels, Topic C1.2 considers bonding in small molecules and temperature changes in chemical reactions. Topic C1.3 explores the evidence for climate change, asking why it might be occurring and how serious a threat it is. You consider environmental and health consequences of some air pollutants and climate change, and learn how scientists are helping to provide options for improving air quality and combatting global warming. Finally, Topic C1.4 explores the need for increasing the amount of potable water worldwide, and techniques for obtaining potable water from ground, waste and salt water. Chapter C1 Air and water (Revision for OCR GCSE 91 Twenty First Century Science Combined Science B chemistry 02, Topics for Chapter C1 "Air and water") Quiz on selected aspects of OCR Twenty First Century GCSE 9-1 Combined Science Chapter C1 "Air and Water"
for HT students
for FT students
HT = higher tier (harder - usually more theory & depth), FT = foundation tier (easier) What you should have learned about air and water before GCSE (91) 21st Century Science Combined Science Chemistry From study at Key Stages 1 to 3 you should:
Chapter C1.1 How has the Earths atmosphere changed over time, and why? (Revision for OCR GCSE 91 Twenty First Century Science Combined Science B chemistry 02, Topics for Chapter C1 "Air and water") The Earth, its atmosphere and its oceans are made up from elements and compounds in different states. The particle can be used to describe the states of these substances and what happens to the particles when they change state. The particle model can be represented in different ways, but these are limited because they do not accurately represent the scale or behaviour of actual particles, they assume that particles are inelastic spheres, and they do not fully take into account the different interactions between particles. The formation of our early atmosphere and oceans, and the state changes involved in the water cycle, can be described using the particle model. Explanations about how the atmosphere was formed and has changed over time are based on evidence, including the types and chemical composition of ancient rocks, and fossil evidence of early life. Explanations include ideas about early volcanic activity followed by cooling of the Earth resulting in formation of the oceans. The evolution of photosynthesising organisms, formation of sedimentary rocks, oil and gas, and the evolution of animals led to changes in the amounts of carbon dioxide and oxygen in the atmosphere. 1. Be able to recall and explain the main features of the particle model in terms of the states of matter and change of state, distinguishing between physical and chemical changes and recognise that the particles themselves do not have the same properties as the bulk substances.
2. (HT only) Be able to explain the limitations of the particle model in relation to changes of state when particles are represented by inelastic spheres. 3. Be able to use ideas about energy transfers and the relative strength of forces between particles to explain the different temperatures at which changes of state occur. 4. Be able to use data to predict states of substances under given conditions. States of Matter Notes on particle theory of gas, liquid & solid, limitations, explaining properties & state changes
Easy multiple choice quiz on "Particle models of gases, liquids and solids and solutions" 4 Easy word-fill quizzes on "The Particles Model of Gases, Liquids and Solids" 7Gwf1 * 7Gwf2 * 7Gwf3 * 7Gwf4 3 Linked easy quizzes on "The States of Matter" States1mp * States2mp * States3mp (very basic questions) 5. Be able to interpret evidence for how it is thought the atmosphere was originally formed. 6. Be able to describe how it is thought an oxygen-rich atmosphere developed over time.
Our modern lifestyle has created a high demand for energy. Combustion of fossil fuels for transport and energy generation leads to emissions of pollutants. Carbon monoxide, sulfur dioxide, nitrogen oxides and particulates directly harm human health. Some pollutants cause indirect problems to humans and the environment by the formation of acid rain and smog. Scientists monitor the concentration of these pollutants in the atmosphere and strive to develop approaches to maintaining air quality. The combustion reactions of fuels and the formation of pollutants can be represented using word and symbol equations. The formulae involved in these reactions can be represented by models, diagrams or written formulae. The equations should be balanced. When a substance chemically combines with oxygen it is an example of oxidation. Combustion reactions are therefore oxidation. Some gases involved in combustion reactions can be identified by their chemical reactions. 7. Be able to describe the major sources of carbon monoxide and particulates (incomplete combustion), sulfur dioxide (combustion of sulfur impurities in fuels), oxides of nitrogen (oxidation of nitrogen at high temperatures and further oxidation in the air)
8. Be able to explain the problems caused by increased amounts of these substances and describe approaches to decreasing the emissions of these substances into the atmosphere including the use of catalytic converters, low sulfur petrol and gas scrubbers to decrease emissions.
9. Be able to use chemical symbols to write the formulae of elements and simple covalent compounds.
10. Be able to use the names and symbols of common elements and compounds and the principle of conservation of mass to write formulae and balanced chemical equations.
11. Be able to use arithmetic computations and ratios when balancing equations.
12. Be able to describe tests to identify oxygen, hydrogen and carbon dioxide.
13. Be able to explain oxidation in terms of gain of oxygen.
Chapter C1.2 Why are there temperature changes in chemical reactions? (Revision for OCR GCSE 91 Twenty First Century Science Combined Science B chemistry 02, Topics for Chapter C1 "Air and water") When a fuel is burned in oxygen the surroundings are warmed; this is an example of an exothermic reaction. There are also chemical reactions that cool their surroundings; these are endothermic reactions. Energy has to be supplied before a fuel burns. For all reactions, there is a certain minimum energy needed to break bonds so that the reaction can begin. This is the activation energy. The activation energy, and the amount of energy associated with the reactants and products, can be represented using a reaction profile. Atoms are rearranged in chemical reactions. This means that bonds between the atoms must be broken and then reformed. Breaking bonds requires energy (the activation energy) whilst making bonds gives out energy. (HT only) Energy changes in a reaction can be calculated if we know the bond energies involved in the reaction. All help links for C1.2 sections 1. to 7. listed after 7. 1. Be able to distinguish between endothermic and exothermic reactions on the basis of the temperature change of the surroundings.
2. Be able to draw and label a reaction profile for an exothermic and an endothermic reaction, identifying activation energy. 3. Be able to explain activation energy as the energy needed for a reaction to occur. 4. Be able to interpret charts and graphs when dealing with reaction profiles. 5. (HT only) Be able to calculate energy changes in a chemical reaction by considering bond breaking and bond making energies 6. Be able to carry out arithmetic computations when calculating energy changes.
Chapter C1.3 What is the evidence for climate change, why is it occurring? (Revision for OCR GCSE 91 Twenty First Century Science Combined Science B chemistry 02, Topics for Chapter C1 "Air and water") Some electromagnetic radiation from the Sun passes through the atmosphere and is absorbed by the Earth warming it. The warm Earth emits infrared radiation which some gases, including carbon dioxide and methane, absorb and re-emit in all directions; this keeps the Earth warmer than it would otherwise be and is called the greenhouse effect. Without the greenhouse effect the Earth would be too cold to support life. The proportion of greenhouse gases in the Earths atmosphere has increased over the last 200 years as a result of human activities. There are correlations between changes in the composition of the atmosphere, consumption of fossil fuels and global temperatures over time. Although there are uncertainties in the data, most scientists now accept that recent climate change can be explained by increased greenhouse gas emissions. Patterns in the data have been used to propose models to predict future climate changes. As more data is collected, the uncertainties in the data decrease, and our confidence in models and their predictions increases. Scientists aim to reduce emissions of greenhouse gases, for example by reducing fossil fuel use and removing gases from the atmosphere by carbon capture and reforestation. These actions need to be supported by public regulation. Even so, it is difficult to mitigate the effect of emissions due to the very large scales involved. Each new measure may have unforeseen impacts on the environment, making it difficult to make reasoned judgments about benefits and risks. 1. Be able to describe the greenhouse effect in terms of the interaction of radiation with matter.
2. Be able to evaluate the evidence for additional anthropogenic causes of climate change, including the correlation between change in atmospheric carbon dioxide concentration and the consumption of fossil fuels, and describe the uncertainties in the evidence base 3. Be able to describe the potential effects of increased levels of carbon dioxide and methane on the Earths climate, including where crops can be grown, extreme weather patterns, melting of polar ice and flooding of low land 4. Be able to describe how the effects of increased levels of carbon dioxide and methane may be mitigated, including consideration of scale, risk and environmental implications 5. Be able to extract and interpret information from charts, graphs and tables. 6. Be able to use orders of magnitude to evaluate the significance of data
Greenhouse effect, global warming, climate change, carbon footprint from fossil fuel burning Notes for 1. to 6. Chapter C1.4 How can scientists help improve the supply of potable water? (Revision for OCR GCSE 91 Twenty First Century Science Combined Science B chemistry 02, Topics for Chapter C1 "Air and water") The increase in global population means there is a greater need for potable water. Obtaining potable water depends on the availability of waste, ground or salt water and treatment methods. Chlorine is used to kill microorganisms in water. The benefits of adding chlorine to water to stop the spread of waterborne diseases outweigh risks of toxicity. In some countries the chlorination of water is subject to public regulation, but other parts of the world are still without chlorinated water and this leads to a higher risk of disease. 1. Be able to describe the principal methods for increasing the availability of potable water, in terms of the separation techniques used, including the ease of treating waste, ground and salt water including filtration and membrane filtration; aeration, use of bacteria; chlorination and distillation (for salt water).
2. Be able to describe a test to identify chlorine (using blue litmus paper).
Chapter C2: Chemical patterns (Revision for OCR GCSE 91 Twenty First Century Science Combined Science B chemistry 02, Topics for Chapter C2 "Chemical patterns") Overview of Chapter C2 Chemical patterns This chapter features a central theme of modern chemistry: it traces the development of ideas about the structure of the atom and the arrangement of elements in the modern Periodic Table. Both stories show how scientific theories develop as new evidence is made available that either supports or contradicts current ideas. Atomic structure is used to help explain the behaviour of the elements. Trends and patterns shown by the physical and chemical properties in groups and in the transition metals are studied. The first two topics of the
chapter give opportunities for learners to develop understanding of
ideas about science; how scientific knowledge develops, the
relationship between evidence and explanations, and Topic C2.1 looks at the development of ideas about the atom and introduces the modern model for atomic structure, including electron arrangements. Topic C2.2 considers the development of the modern Periodic Table and the patterns that exist within it, focusing on Groups 1 and 7, with some reference to Group 0. Topic C2.3 focuses on extending an understanding of atomic structure to explain the ionic bonding between ions in ionic compound. This leads on to Topic C2.4 which studies using equations and symbols to summarise reactions. Chapter C2 Chemical patterns (Revision for OCR GCSE 91 Twenty First Century Science Combined Science B chemistry 02, Topics for Chapter C2 "Chemical patterns") Quiz on selected aspects of OCR Twenty First Century GCSE 9-1 Combined Science Chapter C2 "Chemical patterns" Higher Tier/Foundation Tier (no ionic bonding questions here, see C4 quizzes)
for HT students
for FT students
HT = higher tier (harder - usually more theory & depth), FT = foundation tier (easier) 1st drafts 21st Century chemistry quizzes What you should have learned about Chemical Patterns before GCSE (91) 21st Century Combined Science Chapter 2 Chemical patterns From study at Key Stages 1 to 3 you should:
Chapter C2.1 How have our ideas about atoms developed over time? (Revision for OCR GCSE 91 Twenty First Century Science Combined Science B chemistry 02, Topics for Chapter C2 "Chemical patterns") The modern model of the atom developed over time. Stages in the development of the model included ideas by the ancient Greeks (4 element ideas), Dalton (first particle model), Thomson (plum pudding model), Rutherford (idea of atomic nucleus) and Bohr (shells of electrons). Models were rejected, modified and extended as new evidence became available. The development of the atomic model involved scientists suggesting explanations, making and checking predictions based on their explanations, and building on each others work. The Periodic Table can be used to find the atomic number and relative atomic mass of an atom of an element, and then work out the numbers of protons, neutrons and electrons. The number of electrons in each shell can be represented by simple conventions such as dots in circles or as a set of numbers (for example, sodium as 2.8.1). Atoms are small about 10-10 m across, and the nucleus is at the centre, about a hundred-thousandth of the diameter of the atom. Molecules are larger, containing from two to hundreds of atoms. Objects that can be seen with the naked eye contain millions of atoms. 1. Be able to describe how and why the atomic model has changed over time to include the main ideas of Dalton, Thomson, Rutherford and Bohr
2. Be able to describe the atom as a positively charged nucleus surrounded by negatively charged electrons, with the nuclear radius much smaller than that of the atom and with most of the mass in the nucleus. 3. Be able to recall relative charges and approximate relative masses of protons, neutrons and electrons. 4. Be able to estimate the size and scale of atoms relative to other particles. 5. Be able to recall the typical size (order of magnitude) of atoms and small molecules. 6. Be able to relate size and scale of atoms to objects in the physical world. 7. Be able to calculate numbers of protons, neutrons and electrons in atoms, given atomic number and mass number of isotopes or by extracting data from the Periodic Table.
Chapter C2.2 What does the Periodic Table tell us about the elements? (Revision for OCR GCSE 91 Twenty First Century Science Combined Science B chemistry 02, Topics for Chapter C2 "Chemical patterns") Elements in the modern Periodic Table are arranged in periods and groups, based on their atomic numbers. Elements in the same group have the same number of electrons in their outer shells. The number of electron shells increases down a group but stays the same across a period. Mendeleev proposed the first arrangement of elements in the Periodic Table. Although he did not know about atomic structure, he reversed the order of some elements with respect to their masses, left gaps for undiscovered elements and predicted their properties. His ideas were accepted because when certain elements were discovered they fitted his gaps and the development of a model for atomic structure supported his arrangement. The later determination of the number of protons in atoms provided an explanation for the order he proposed. The Periodic Table shows repeating patterns in the properties of the elements. Metals and non-metals can be identified by their position in the Periodic Table and by comparing their properties (physical properties including electrical conductivity). Properties of elements within a group show trends. The reactivity of Group 1 metals elements increases down the group, shown by their reactivity with moist air, water and chlorine. The Group 7 halogens are non-metals and become less reactive down the group. This is shown in reactions such as their displacement reactions with compounds of other halogens in the group. 1. Be able to explain how the position of an element in the Periodic Table is related to the arrangement of electrons in its atoms and hence to its atomic number.
2. Be able to describe how Mendeleev organised the elements based on their properties and relative atomic masses. 3. Be able to describe how discovery of new elements and the ordering elements by atomic number supports Mendeleevs decisions to leave gaps and reorder some elements. 4. Be able to describe metals and non-metals and explain the differences between them on the basis of their characteristic physical and chemical properties, including melting point, boiling point, state and appearance, density, formulae of compounds and relative reactivity and electrical conductivity.
5. Be able to recall the simple properties of Group 1 elements including their reaction with moist air, water, and chlorine.
6. Be able to recall the simple properties of Group 7 elements including their states and colours at room temperature and pressure, their colours as gases, their reactions with Group 1 elements and their displacement reactions with other metal halides.
7. Be able to predict possible reactions and probable reactivity of elements from their positions in the Periodic Table.
8. Be able to describe experiments to identify the reactivity pattern of Group 7 elements including displacement reactions.
9. Be able to describe experiments to identify the reactivity pattern of Group 1 elements.
Chapter C2.3 How do metals and non-metals combine to form compounds? (Revision for OCR GCSE 91 Twenty First Century Science Combined Science B chemistry 02, Topics for Chapter C2 "Chemical patterns") Group 0 contains elements with a full outer shell of electrons. This arrangement is linked to their inert, unreactive properties. They exist as single atoms and hence are gases with low melting and boiling points. Group 1 elements combine with Group 7 elements by ionic bonding. This involves a transfer of electrons leading to charged ions. Atoms and ions can be represented using dot and cross diagrams as simple models. Metals, such as Group 1 metals, lose electrons from the outer shell of their atoms to form ions with complete outer shells and with a positive charge. Non-metals, such as Group 7, form ions with a negative charge by gaining electrons to fill their outer shell. The number of electrons lost or gained determines the charge on the ion. The properties of ionic compounds such as Group 1 halides can be explained in terms of the ionic bonding. Positive ions and negative ions are strongly attracted together and form giant lattices. Ionic compounds have high melting points in comparison to many other substances due to the strong attraction between ions which means a large amount of energy is needed to break the attraction between the ions. They dissolve in water because their charges allow them to interact with water molecules. They conduct electricity when molten or in solution because the charged ions can move, but not when solid because the ions are held in fixed positions. The arrangement of ions can be represented in both 2-D and 3-D. These representations are simple models which have limitations, for example they do not fully show the nature or movement of the electrons or ions, the interaction between the ions, their arrangement in space, their relative sizes or scale (IaS3).
1. Be able to recall the simple properties of Group 0 including their low melting and boiling points, their state at room temperature and pressure and their lack of chemical reactivity.
2. Be able to explain how observed simple properties of Groups 1, 7 and 0 depend on the outer shell of electrons of the atoms and predict properties from given trends down the groups.
3. Be able to explain how the reactions of elements are related to the arrangement of electrons in their atoms and hence to their atomic number. 4. Be able to explain how the atomic structure of metals and non-metals relates to their position in the Periodic Table.
5. Be able to describe the nature and arrangement of chemical bonds in ionic compounds.
6. Be able to explain ionic bonding in terms of electrostatic forces and transfer of electrons
7. Be able to calculate numbers of protons, neutrons and electrons in atoms and ions, given atomic number and mass number or by using the Periodic Table.
8. Be able to construct dot and cross diagrams for simple ionic substances 9. Be able to explain how the bulk properties of ionic materials are related to the type of bonds they contain.
10. Be able to use ideas about energy transfers and the relative strength of attraction between ions to explain the melting points of ionic compounds compared to substances with other types of bonding.
11. Be able to describe the limitations of particular representations and models of ions and ionically bonded compounds, including dot and cross diagrams, and 3-D representations 12. Be able to translate information between diagrammatic and numerical forms and represent three dimensional shapes in two dimensions and vice versa when looking at chemical structures for ionic compounds.
Chapter C2.4 How are equations used to represent chemical reactions? (Revision for OCR GCSE 91 Twenty First Century Science Combined Science B chemistry 02, Topics for Chapter C2 "Chemical patterns") The reactions of Group 1 and Group 7 elements can be represented using word equations and balanced symbol equations with state symbols. The formulae of ionic compounds, including Group 1 and Group 7 compounds can be worked out from the charges on their ions. Balanced equations for reactions can be constructed using the formulae of the substances involved, including hydrogen, water, halogens (chlorine, bromine and iodine) and the hydroxides, chlorides, bromides and iodides (halides) of Group 1 metals. 1. Be able to use chemical symbols to write the formulae of elements and simple covalent and ionic compounds. 2. Be able to use the formulae of common ions to deduce the formula of Group 1 and Group 7 compounds. 3. Be able to use the names and symbols of the first 20 elements, Groups 1, 7 and 0 and other common elements from a supplied Periodic Table to write formulae and balanced chemical equations where appropriate. 4. Be able to describe the physical states of products and reactants using state symbols (s, l, g and aq).
Chapter C3: Chemicals of the natural environment (Revision for OCR GCSE 91 Twenty First Century Science Combined Science B chemistry 02, Topics for Chapter C3 "Chemicals of the natural environment") Overview of Chapter C3 Chemicals of the natural environment (GCSE 21st Century Combined Science) Our way of life depends on a wide range of products made from natural resources. The Earths crust provides us with metal ores and crude oil and our use of these impacts on the natural environment. Chemistry is fundamental to an understanding of the scale and significance of this human activity. In Topic C3.1 the properties of metals are related to their structure and bonding. In Topic C3.2 you discover why the reactivity of a metal determines how it is extracted from its ores and how new technologies enable us to extract metals from poor quality ores. Electrolysis is explained in Topic C3.3, and you learn about the wide variety of products made by electrolysis. Finally, Topic C3.4 covers the separation of crude oil into fractions and the use of these fractions to make other chemicals and polymers. Within this context you study the properties of simple molecules in relation to covalent bonding and intermolecular forces. Learning about chemicals of the natural environment before GCSE (91) From study at Key Stages 1 to 3 you should:
Chapter C3 Chemicals of the natural environment (Revision for OCR GCSE 91 Twenty First Century Science Combined Science B chemistry 02, Topics for Chapter C3 "Chemicals of the natural environment") Quiz on selected aspects of OCR Twenty First Century GCSE 9-1 Combined Science chemistry Chapter C3 "Chemicals of the natural environment" Higher Tier/Foundation Tier (no metallic bonding questions here - see C4 quizzes, but does include some polymer questions based on aspects of C4)
for HT
for FT
HT = higher tier (harder - usually more theory & depth), FT = foundation tier (easier) Chapter C3.1 How are the atoms held together in a metal? (Revision for OCR GCSE 91 Twenty First Century Science Combined Science B chemistry 02, Topics for Chapter C3 "Chemicals of the natural environment") Chemists use a model of metal structure to explain the properties of metals (IaS3). In the model, metal atoms are arranged closely together in a giant structure, held together by attraction between the positively charged atoms and a sea of negatively charged electrons. Metals are malleable and ductile because the ions can slide over each other but still be held together by the electrons; they conduct electricity and heat because their electrons are free to move; and they have high boiling points and melting points due to the strong electrostatic attraction between metal ions and the electrons. These properties of metals make them useful. 1. Be able to describe the nature and arrangement of chemical bonds in metals.
2. Be able to explain how the bulk properties of metals are related to the type of bonds they contain.
Chapter C3.2 How are metals with different reactivities extracted? (Revision for OCR GCSE 91 Twenty First Century Science Combined Science B chemistry 02, Topics for Chapter C3 "Chemicals of the natural environment") Metals can be placed in an order of reactivity by looking at their reactions with water, dilute acid and compounds of other metals. The relative reactivity of metals enables us to make predictions about which metals react fastest or which metal will displace another. When metals react they form ionic compounds. The metal atoms gain one or more electrons to become positive ions. The more easily this happens the more reactive the metal. These reactions can be represented by word and symbol equations including state symbols. (HT only) Ionic equations show only the ions that change in the reaction and show the gain or loss of electrons. They are useful for representing displacement reactions because they show what happens to the metal ions during the reaction. The way a metal is extracted depends on its reactivity. Some metals are extracted by reacting the metal compound in their ores with carbon. Carbon is a non-metal but can be placed in the reactivity series of the metals between aluminium and zinc. Metals below carbon in the reactivity series are extracted from their ores by displacement by carbon. The metal in the ore is reduced and carbon is oxidised. Highly reactive metals above carbon in the reactivity series are extracted by electrolysis. Scientists are developing methods of extracting the more unreactive metals from their ores using bacteria or plants. These methods can extract metals from waste material, reduce the need to extract new ores, reduce energy costs, and reduce the amount of toxic metals in landfill. However, these methods do not produce large quantities of metals quickly. 1. Be able to deduce an order of reactivity of metals based on experimental results including reactions with water, dilute acid and displacement reactions with other metals.
2. Be able to explain how the reactivity of metals with water or dilute acids is related to the tendency of the metal to form its positive ion to include potassium, sodium, calcium, aluminium, magnesium, zinc, iron, lead, [hydrogen], copper, silver.
3. Be able to use the names and symbols of common elements and compounds and the principle of conservation of mass to write formulae and balanced chemical equations and (HT only) ionic equations. 4. Be able to explain, using the position of carbon in the reactivity series, the principles of industrial processes used to extract metals, including the extraction of zinc.
5. Be able to explain why electrolysis is used to extract some metals from their ores.
6. (HT only) Be able to evaluate alternative biological methods of metal extraction (bacterial and phytoextraction).
Chapter C3.3 What are electrolytes and what happens during electrolysis? (Revision for OCR GCSE 91 Twenty First Century Science Combined Science B chemistry 02, Topics for Chapter C3 "Chemicals of the natural environment") Electrolysis is used to extract reactive metals from their ores. Electrolysis is the decomposition of an electrolyte by an electric current. Electrolytes include molten and dissolved ionic compounds. In both cases the ions are free to move. During electrolysis non-metal ions lose electrons to the anode to become neutral atoms. Metal (or hydrogen) ions gain electrons at the cathode to become neutral atoms. The addition or removal of electrons can be used to identify which species are reduced and which are oxidised. These changes can be summarised using half equations. Electrolysis is used to extract reactive metals from their molten compounds. During the electrolysis of aluminium, aluminium oxide is heated to a very high temperature. Positively charged aluminium ions gain electrons from the cathode to form atoms. Oxygen ions lose electrons at the anode and form oxygen molecules which react with carbon electrodes to form carbon dioxide. The process uses a large amount of energy for both the high temperature and the electricity involved in electrolysis. Some extraction methods, such as the recovery of metals from waste heaps, give a dilute aqueous solution of metals ions. When an electric current is passed through an aqueous solution the water is electrolysed as well as the ionic compound. Less reactive metals such as silver or copper form on the negative electrode. If the solution contains ions of more reactive metals, hydrogen gas forms from the hydrogen ions from the water. Similarly, oxygen usually forms at the positive electrode from hydroxide ions from the water. A concentrated solution of chloride ions forms chlorine at the positive electrode.
1. Be able to describe electrolysis in terms of the ions present and reactions at the electrodes.
2. Be able to predict the products of electrolysis of binary ionic compounds in the molten state.
3. Be able to recall that metals (or hydrogen) are formed at the cathode and non-metals are formed at the anode in electrolysis using inert electrodes.
4. (HT only) Be able to use the names and symbols of common elements and compounds and the principle of conservation of mass to write half equations. 5. (HT only) Be able to explain reduction and oxidation in terms of gain or loss of electrons, identifying which species are oxidised and which are reduced.
6. Be able to explain how electrolysis is used to extract some metals from their ores including the extraction of aluminium.
7. Be able to describe competing reactions in the electrolysis of aqueous solutions of ionic compounds in terms of the different species present, including the formation of oxygen, chlorine and the discharge of metals or hydrogen linked to their relative reactivity.
8. Be able to describe the technique of electrolysis of an aqueous solution of a salt.
Chapter C3.4 Why is crude oil important as a source of new materials? (Revision for OCR GCSE 91 Twenty First Century Science Combined Science B chemistry 02, Topics for Chapter C3 "Chemicals of the natural environment") Crude oil is mixture of hydrocarbons. It is used as a source of fuels and as a feedstock for making chemicals (including polymers) for a very wide range of consumer products. Almost all of the consumer products we use involve the use of crude oil in their manufacture or transport. Crude oil is finite. If we continue to burn it at our present rate it will run out in the near future. Crude oil makes a significant positive difference to our lives, but our current use of crude oil is not sustainable. Decisions about the use of crude oil must balance short-term benefits with the need to conserve this resource for the future. Crude oil is a mixture. It needs to be separated into groups of molecules of similar size called fractions. This is done by fractional distillation. Fractional distillation depends on the different boiling points of the hydrocarbons, which in turn is related to the size of the molecules and the intermolecular forces between them. The fractions are mixtures, mainly of alkanes, with a narrow range of boiling points. The first four alkanes show typical properties of a homologous series: each subsequent member increases in size by CH2, they have a general formula and show trends in their physical and chemical properties. 1. Be able to recall that crude oil is a main source of hydrocarbons and is a feedstock for the petrochemical industry.
2. Be able to explain how modern life is crucially dependent upon hydrocarbons and recognise that crude oil is a finite resource. 3. Be able to describe and explain the separation of crude oil by fractional distillation.
4. Be able to describe the fractions of crude oil as largely a mixture of compounds of formula CnH2n+2 which are members of the alkane homologous series of hydrocarbons.
5. Be able to use ideas about energy transfers and the relative strength of chemical bonds and intermolecular forces to explain the different temperatures at which changes of state occur.
6. Be able to deduce the empirical formula of a compound from the relative numbers of atoms present or from a model or diagram and vice versa.
7. Be able to use arithmetic computation and ratio when determining empirical formulae.
8. Be able to describe the arrangement of chemical bonds in simple molecules.
9. Be able to explain covalent bonding in terms of the sharing of electrons. 10. Be able to construct dot and cross diagrams for simple covalent substances.
11. Be able to represent three dimensional shapes in two dimensions and vice versa when looking at chemical structures for simple molecules. 12. Be able to describe the limitations of dot and cross diagrams, ball and stick models and two and three dimensional representations when used to represent simple molecules. 13. Be able to translate information between diagrammatic and numerical forms. 14. Be able to explain how the bulk properties of simple molecules are related to the covalent bonds they contain and their bond strengths in relation to intermolecular forces.
15. Be able to describe the production of materials that are more useful by cracking.
ALL OCR GCSE (Grade 9-1) Level 1/Level 2 TWENTY FIRST CENTURY SCIENCE B specifications and syllabus revision summary links Be aware that both Paper 1 and Paper 2 for biology, chemistry or physics assess content from ALL 6 chapters 1-6 !!! Paper 1 is called "Breadth in biology/chemistry/physics" and Paper 2 is called "Depth in biology/chemistry/physics" Watch out for HT Only sections AND make sure you know exactly which GCSE science course you are doing! See also OCR Gateway Sciences A Revision Links
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INDEX
for all links
Chapter C1 "Air and Water" QUIZ (OCR 21st GCSE 9-1
Chemistry-Combined Science B)
