Oxford AQA International GCSE Chemistry

Full syllabus for OxfordAQA IGCSE Chemistry specification 9202

CHEMISTRY (Oxford AQA International GCSE Chemistry)

ATOMIC STRUCTURE AND THE PERIODIC TABLE (Oxford AQA International GCSE Chemistry)

Atoms are the building blocks of all materials and knowledge of atomic structure and the periodic table are fundamental to the learning associated with all the following sections.

Solids liquids and gases (Oxford AQA International GCSE Chemistry)

a. Matter can be classified in terms of the three states of matter.
Students should be familiar with states of matter and be able to name each inter-conversion process. They should be able to describe and explain their inter-conversion in terms of how the particles are arranged and their movement. They should understand the energy changes that accompany changes of state.
b. Evidence for the existence of particles can be obtained from simple experiments.
Students should be familiar with simple diffusion experiments such as Br₂/air, NH₃/HCl, KMnO₄/water

A simple model of the atom (Oxford AQA International GCSE Chemistry)

a. All substances are made of atoms. A substance that is made of only one sort of atom is called an element. There are about 100 different elements. Elements are shown in the periodic table.
b. Atoms of each element are represented by a chemical symbol, eg O represents an atom of oxygen. Knowledge of the chemical symbols for elements other than those named in the specification is not required.
c. Atoms have a small central nucleus, made up of protons and neutrons, and around which there are electrons.
Students should be aware that the atomic model has changed over time.
d. The relative electrical charges and name of particle:  Proton +1.  Neutron 0,  Electron –1
e. In an atom, the number of electrons is equal to the number of protons in the nucleus. Atoms have no overall electrical charge.
f. The number of protons in an atom of an element is its atomic number. The sum of the protons and neutrons in an atom is its mass number.
Students will be expected to calculate the numbers of each sub-atomic particle in an atom from its atomic number and mass number.

g. Atoms of the same element can have different numbers of neutrons; these atoms are called isotopes of that element.

h. Atoms can be represented as shown in this example: mass number of 23, atomic number 11 for sodium
i. Electrons occupy particular energy levels. Each electron in an atom is at a particular energy level (in a particular shell). The electrons in an atom occupy the lowest available energy levels (innermost available shells).
Students may answer questions in terms of either energy levels or shells e.g. diagram on the right.
Students should be able to represent the electronic structure of the first twenty elements of the periodic table in the following forms

j. The relative masses of protons, neutrons and electrons are:

k. The relative atomic mass of an element (Ar) compares the mass of atoms of the element with the ¹²C isotope (carbon-12). It is an average value for the isotopes of the element.
Students will not be expected to calculate relative atomic masses from isotopic abundances.

THE PERIODIC TABLE (Oxford AQA International GCSE Chemistry)

a. The periodic table is arranged in order of atomic (proton) number. Elements with similar properties are in columns, known as groups. The table is called a periodic table because similar properties occur at regular intervals.
Students should know that the current periodic table is based on the work of Mendeleev.
b. Elements in the same group in the periodic table have the same number of electrons in their highest energy level (outer electrons) and this gives them similar chemical properties.
Students should know that basing the periodic table on groups of elements with similar properties has allowed for the prediction of elements which were still to be discovered.
c. The elements in Group 0 of the periodic table are called the noble gases. They are unreactive because their atoms have stable arrangements of electrons.
Students should know that the noble gases have eight electrons in their outer energy level, except for helium, which has only two electrons.

STRUCTURE, BONDING AND THE PROPERTIES OF MATTER (Oxford AQA International GCSE Chemistry)

This section examines how atoms interact to form chemical bonds and how these bonds determine the properties and uses of materials.

Chemical bonds: ionic, covalent and metallic (Oxford AQA International GCSE Chemistry)

a. Compounds are substances in which atoms of two or more elements are chemically combined.
b. Chemical bonding involves either transferring or sharing electrons in the highest occupied energy levels (outer shells) of atoms in order to achieve the electron arrangement of a noble gas.
c. When atoms form chemical bonds by transferring electrons, they form ions. Atoms that lose electrons become positively charged ions. Atoms that gain electrons become negatively charged ions. Ions have the electron arrangement of a noble gas (Group 0). Compounds formed from metals and non-metals consist of ions.
Students should know that metals form positive ions, whereas non-metals form negative ions.
Students should be able to represent the electron arrangement of ions in the following form:

e.g. for the ionic compound sodium chloride, made up of the sodium ion (Na⁺) and chloride ion (Cl^-) combination.

Students should be able to relate the charge on simple ions to the group number of the element in the periodic table

d. The elements in Group 1 of the periodic table, the alkali metals, all react with non-metal elements to form ionic compounds in which the metal ion has a single positive charge.
Knowledge of the chemical properties of alkali metals is limited to their reactions with non-metal elements and water.
e. The elements in Group 7 of the periodic table, the halogens, all react with metals to form ionic compounds in which the halide ions have a single negative charge.
Knowledge of the chemical properties of the halogens is limited to reactions with metals and displacement of less reactive halogens.
f. An ionic compound is a giant structure of ions. Ionic compounds are held together by strong electrostatic forces of attraction between oppositely charged ions. These forces act in all directions in the lattice and this is called ionic bonding.
Students should be familiar with the structure of sodium chloride but do not need to know the structures of other ionic compounds.
Students given appropriate information, should be able to draw or complete diagrams to show how elements form ions and ionic compounds.

g. When atoms share pairs of electrons, they form covalent bonds. These bonds between atoms are strong.
Some covalently bonded substances, such as H₂, Cl₂ , O₂, N₂, HCl, H₂O, NH₃ and CH₄, consist of simple molecules. Others, such as diamond and silicon dioxide, have giant covalent structures (macromolecules).
Students should be able to represent the covalent bonds in molecules such as water, ammonia, hydrogen, hydrogen chloride, methane and oxygen in the following forms:
e.g. for ammonia (NH₃) be familiar with these different styles
   
Students, given appropriate information, should be able to draw or complete diagrams to show how elements form covalent compounds by sharing electrons.
Students should be able to recognise other simple molecules and giant structures from diagrams that show their bonding

h. Compounds formed from non-metals consist of molecules. In molecules, the atoms are held together by covalent bonds.
i. Metals consist of giant structures of atoms arranged in a regular pattern.
j. The electrons in the highest occupied energy levels (outer shell) of metal atoms are delocalised and so free to move through the whole structure. This corresponds to a structure of positive ions with electrons between the ions holding them together by strong electrostatic attractions. The bonding in metals is represented in the following form:

Showing the original neutral atoms and the actual ions and delocalised electrons in the real metallic lattice of a metal crystal.

How bonding and structure are related to the properties of substances

a. Ionic compounds have regular structures (giant ionic lattices) in which there are strong electrostatic forces of attraction in all directions between oppositely charged ions.
These compounds have high melting points and high boiling points because of the large amounts of energy needed to break the many strong bonds.
b. When melted or dissolved in water, ionic compounds conduct electricity because the ions are free to move and carry the current.
Knowledge of the structures of specific ionic compounds other than sodium chloride is not required.
c. Substances that consist of simple molecules are gases, liquids or solids that have relatively low melting points and boiling points.
d. Substances that consist of simple molecules have only weak forces between the molecules (intermolecular forces). It is these intermolecular forces that are overcome, not the covalent bonds, when the substance melts or boils.
Students need to understand that intermolecular forces are weak compared with covalent bonds.
e. Substances that consist of simple molecules do not conduct electricity because the molecules do not have an overall electric charge.
f. Atoms that share electrons can also form giant structures or macromolecules. Diamond and graphite (forms of carbon) and silicon dioxide (silica) are examples of giant covalent structures (lattices) of atoms. All the atoms in these structures are linked to other atoms by strong covalent bonds and so they have very high melting points.
Students should be able to recognise other giant structures or macromolecules from diagrams showing their bonding.
g. Metals conduct heat and electricity because of the delocalised electrons in their structures.
Students should know that conduction depends on the ability of electrons to move through the metal.

Structure and bonding in carbon (Oxford AQA International GCSE Chemistry)

a. The element carbon can form four covalent bonds.
b. In diamond, each carbon atom forms four covalent bonds with other carbon atoms in a giant covalent structure, so diamond is very hard.
c. In graphite, each carbon atom bonds to three others, forming layers. The layers are free to slide over each other because there are no covalent bonds between the layers and so graphite is soft and slippery.
Extension Tier students should be able to explain the properties of graphite in terms of weak forces between the layers.
d. In graphite, one electron from each carbon atom is delocalised. These delocalised electrons allow graphite to conduct heat and electricity.
Students should realise that graphite is similar to metals in that it has delocalised electrons.

e. Carbon can also form fullerenes with different numbers of carbon atoms. Fullerenes can be used for drug delivery into the body, in lubricants, as catalysts, and in nanotubes for reinforcing materials, eg in tennis racquets.
Students are only required to know that the structure of fullerenes is based on hexagonal rings of carbon atoms

NANOPARTICLES (Oxford AQA International GCSE Chemistry)
Nanoscience refers to structures that are 1–100 nm in size, of the order of a few hundred atoms. Nanoparticles show properties different from those for the same materials in bulk and have a high surface area to volume ratio, which may lead to the development of new computers, new catalysts, new coatings, highly selective sensors, stronger and lighter construction materials, and new cosmetics such as suntan creams and deodorants.
Students should know what is meant by nanoscience and nanoparticles and should consider some of the applications of these materials, but do not need to know specific examples or properties.
Questions may be set on information that is provided about these materials and relating their use to their structure

CHEMICAL CHANGES (Oxford AQA International GCSE Chemistry)

The group of materials known as metals are explored in more detail including how atoms are rearranged to form new substances in chemical reactions.

Metals (Oxford AQA International GCSE Chemistry)

a. Metals are useful materials because they are good conductors of heat and electricity. They can be bent or hammered into shape because the layers of atoms in metals are able to slide over each other.
b. An alloy is a mixture of at least two elements, at least one of which is a metal. Alloys often have properties that are different to the metals they contain. This makes them more useful than the pure metals alone.
Steels are a mixture of iron with carbon and sometimes other metals.
Students may be given information on the composition of specific alloys so that they can evaluate their uses.
c. Copper is useful for electrical wiring and plumbing because it has the following properties:
• it is a good conductor of heat and electricity
• it can be bent but is hard enough to be used to make pipes or tanks
• it does not react with water.

The reactivity series of metals (Oxford AQA International GCSE Chemistry)

a. Metals can be arranged in an order of their reactivity from their reactions with water and dilute acids.
Students should be able to recall and describe the reactions, if any, of potassium, sodium, lithium, calcium, magnesium, zinc, iron and copper with water or dilute acids. Students should be able, where appropriate, to place them in order of reactivity.
b. Displacement reactions involving metals and their compounds in aqueous solution establish positions within the reactivity series.
Students should be able to describe displacement reactions in terms of oxidation and reduction, and to write the ionic equations.
c. Unreactive metals such as gold are found in the Earth as the metal itself but most metals are found as compounds that require chemical reactions to extract the metal.
d. Metals that are less reactive than carbon can be extracted from their oxides by reduction with carbon: for example, iron oxide is reduced in the blast furnace to make iron.
Knowledge and understanding are limited to the reduction of oxides using carbon.
Knowledge of reduction is limited to the removal of oxygen.
Students should understand that oxidation can be described as the gain of oxygen by a substance.
Details of the blast furnace are not required, but students should know the raw materials used and explain the simple chemistry involved, including the use of equations.
Knowledge of the details of the extraction of other metals is not required. Examination questions may provide further information about specific processes for students to interpret or evaluate.
e. Metals that are more reactive than carbon, such as aluminium, are extracted by electrolysis of molten compounds. The use of large amounts of energy in the extraction of these metals makes them expensive.
Knowledge of the details of industrial methods of electrolysis is not required, other than the detail required for aluminium.
f. New ways of extracting copper from low-grade ores are being researched to limit the environmental impact of traditional mining.
Copper can be extracted by phytomining, or by bioleaching.
Students should know and understand that:
• phytomining uses plants to absorb metal compounds and that the plants are burned to produce ash that contains the metal compounds
• bioleaching uses bacteria to produce leachate solutions that contain metal compounds.
Further specific details of these processes are not required.
g. Copper can be obtained from solutions of copper salts by electrolysis.
Students should know the electrode material and be able to write the ionic half equations for the reactions occurring at both electrodes.
h. Copper can be obtained from solutions of copper salts by displacement using scrap iron.
Students should be able to describe this in terms of oxidation and reduction, and to write the ionic equation.
i. We should recycle metals because extracting them uses limited resources, and is expensive in terms of energy and in terms of effects on the environment.
Students are not required to know details of specific examples of recycling, but should understand the benefits of recycling in the general terms specified here

Metal carbonates (Oxford AQA International GCSE Chemistry)

a. The carbonates of magnesium, copper, zinc, calcium and lithium decompose on heating (thermal decomposition) in a similar way.
Students should be aware that not all carbonates of metals in Group 1 of the periodic table decompose at the temperatures reached by a Bunsen burner.
b. Metal carbonates react with acids to produce carbon dioxide, a salt and water.

Electrolysis (Oxford AQA International GCSE Chemistry)

a. When an ionic substance is melted or dissolved in water, the ions are free to move about within the liquid or solution.
b. Passing an electric current through ionic substances that are molten, eg lead bromide, or in solution breaks them down into elements. This process is called electrolysis and the substance broken down is called the electrolyte.
c. During electrolysis, positively charged ions move to the negative electrode (the cathode), and negatively charged ions move to the positive electrode (the anode).

Required practical:
Investigate the products at the anode and cathode in the electrolysis of copper sulfate solution.

d. Oxidation and reduction can be defined as the loss and gain of electrons respectively.
e. At the cathode, positively charged ions gain electrons; at the anode, negatively charged ions lose electrons.
f. Reactions at electrodes can be represented by half equations, for example:
2Cl ^– → Cl₂ + 2e^– or  2Cl^– – 2e^– → Cl₂
Students should be able to write half equations for the reactions occurring at the electrodes during electrolysis, and may be required to complete and balance supplied half equations.
g. If there is a mixture of ions:
• at the cathode, the products formed depend on the reactivity of the elements involved
• at the anode, the products formed also depend on the relative concentrations of the ions present.
h. Electrolysis is used to electroplate objects. This may be for reasons such as appearance, durability and prevention of corrosion. It includes copper plating and silver plating.
i. Aluminium is manufactured by the electrolysis of a molten mixture of aluminium oxide and cryolite.
Aluminium forms at the negative electrode and oxygen at the positive electrode. The positive electrode is made of carbon, which reacts with the oxygen to produce carbon dioxide.
Students should understand why cryolite is used in this process.
Students should be aware that large amounts of energy are needed in the extraction process.
j. The electrolysis of sodium chloride solution produces hydrogen and chlorine. Sodium hydroxide solution is also produced. These are important reagents for the chemical industry, eg sodium hydroxide for the production of soap and chlorine for the production of bleach and plastics.
Students should be able to explain, using ideas related to reactivity, why each of these products is produced

CHEMICAL ANALYSIS (Oxford AQA International GCSE Chemistry)

This section focuses on developing practical skills in chemistry which identify substances and reinforces the idea of a pure substance as consisting of one substance only.

Purity and chromatography (Oxford AQA International GCSE Chemistry)

a. A pure element or compound contains only one substance, with no other substances mixed in. Students should be able to identify substances and assess their purity from melting point and boiling point information.
b. Measures of purity are important in everyday substances such as foodstuffs and drugs.
c. A mixture consists of two or more elements or compounds not chemically combined together. The chemical properties of each substance in the mixture are unchanged. It is possible to separate the substances in a mixture by physical methods, including distillation, filtration and crystallisation.
d. Paper chromatography can be used to analyse substances present in a solution, eg food colourings and inks/dyes.
Students should be able to describe how to carry out paper chromatography separations and Extension Tier students should be able to describe how the components of a mixture can be identified using Rf
values. They have to be aware that solvents other than water can be used.
e. Chromatography involves a stationary and a mobile phase and separation depends on the relative solubilities of the components.
Students should be able to suggest chromatographic methods for distinguishing pure from impure substances.

IDENTIFICATION OF COMMON GASES (Oxford AQA International GCSE Chemistry)
a. A pop is heard when a lighted splint is placed near hydrogen gas.
b. A glowing splint relights in a test tube of oxygen gas.
c. Carbon dioxide turns limewater (calcium hydroxide solution) cloudy white.
d. Ammonia has a characteristic sharp, choking smell. It also makes damp red litmus paper turn blue. Ammonia forms a white smoke of ammonium chloride when hydrogen chloride gas, from concentrated hydrochloric acid, is held near it.
e. Chlorine has a characteristic sharp, choking smell. It also makes damp blue litmus paper turn red, and then bleaches it white

Identification of ions (Oxford AQA International GCSE Chemistry)

a. Flame tests can be used to identify metal ions. Lithium, sodium, potassium, calcium and barium compounds produce distinctive colours in flame tests:
• lithium compounds result in a crimson flame
• sodium compounds result in a yellow flame
• potassium compounds result in a lilac flame
• calcium compounds result in a red flame
• barium compounds result in a green flame.
Required practical:
Identify the metal ion in an unknown compound using flame testing techniques.
b. Aluminium, calcium and magnesium ions form white precipitates with sodium hydroxide solution but only the aluminium hydroxide precipitate dissolves in excess sodium hydroxide solution.
c. Copper(II), iron(II) and iron(III) ions form coloured precipitates with sodium hydroxide solution. Copper(II) forms a blue precipitate, iron(II) a green precipitate and iron(III) a brown precipitate.
d. Carbonates react with dilute acids to form carbon dioxide. Carbon dioxide produces a white precipitate with limewater, which turns limewater cloudy white.

e. Halide ions in solution produce precipitates with silver nitrate solution in the presence of dilute nitric acid. Silver chloride is white, silver bromide is cream and silver iodide is yellow.
f. Sulfate ions in solution produce a white precipitate with barium chloride solution in the presence of dilute hydrochloric acid.

ACIDS, BASES AND SALTS (Oxford AQA International GCSE Chemistry)

This section looks in greater detail at the properties and applications of acids and bases.

The properties of acids and bases (Oxford AQA International GCSE Chemistry)

a. Metal oxides and hydroxides are bases. Soluble hydroxides are called alkalis.
b. Acids react with bases to form salts. These reactions are called neutralisation reactions.
c. The particular salt produced in any reaction between an acid and a base or alkali depends on:
• the acid used (hydrochloric acid produces chlorides, nitric acid produces nitrates, sulfuric acid produces sulfates)
• the metal in the base or alkali.
d. Ammonia dissolves in water to produce an alkaline solution. It is used to produce ammonium salts.
e. A solution of calcium hydroxide in water (limewater) reacts with carbon dioxide to produce calcium carbonate.
f. Hydrogen ions, H + (aq), make solutions acidic and hydroxide ions, OH– (aq), make solutions alkaline. The pH scale is a measure of the acidity or alkalinity of a solution.
Students should be familiar with the pH scale from 0 to 14, and know that pH 7 is a neutral solution.
Students should be able to describe the use of universal indicator to measure the approximate pH of a solution.
g. In neutralisation reactions, hydrogen ions react with hydroxide ions to produce water. This reaction can be represented by the equation:
H⁺(aq) + OH^–(aq) → H₂O(l)

Preparation of salts (Oxford AQA International GCSE Chemistry)

a. Soluble salts can be made from acids by reacting them with:
• metals – not all metals are suitable; some are too reactive and others are not reactive enough
• insoluble bases – the base is added to the acid until no more will react and the excess solid is filtered off
• alkalis – an indicator can be used to show when the acid and alkali have completely reacted to produce a salt solution.
Students should be able to suggest methods to make a named soluble salt.
b. Salt solutions can be crystallised to produce solid salts.
c. Insoluble salts can be made by mixing appropriate solutions of ions so that a precipitate is formed.
Precipitation can be used to remove unwanted ions from solutions: for example, in treating water for drinking or in treating effluent.
Students should be able to name the substances needed to make a named insoluble salt.

QUANTITATIVE CHEMISTRY (Oxford AQA International GCSE Chemistry)

Conservation of mass is a key concept in chemistry and this is developed during this section. This is then used to develop a quantitative approach to chemical reactions, leading to many opportunities to develop experimental skills through practical work and mathematical skills

Conservation of mass including the quantitative interpretation of chemical equations

a. Chemical reactions can be represented by word equations or by symbol equations.
Students should be able to write word and balanced symbol equations for reactions in the specification.
b. Information about the states of reactants and products can be included in chemical equations.
Students should be able to use the state symbols (g), (l), (s) and (aq) in equations where appropriate.
c. No atoms are lost or made during a chemical reaction so the mass of the products equals the mass of the reactants.
d. The masses of reactants and products can be calculated from balanced symbol equations.
Students should be able to calculate the mass of a reactant or product from information about the masses of the other reactants and products in the reaction and the balanced symbol equation.
e. Even though no atoms are gained or lost in a chemical reaction, it is not always possible to obtain the calculated amount of a product because:
• the reaction may not go to completion because it is reversible
• some of the product may be lost when it is separated from the reaction mixture
• some of the reactants may react in ways different from the expected reaction.

Use of amount of substance in relation to masses of pure substances

a. The relative formula mass (M_r) of a compound is the sum of the relative atomic masses of the atoms in the numbers shown in the formula.
Students are expected to use relative atomic masses in the calculations specified in the subject content.
Students should be able to calculate the relative formula mass (Mr) of a compound from its formula.
b. The percentage by mass of an element in a compound can be calculated from the relative atomic mass of the element in the formula and the relative formula mass of the compound.
c. The empirical formula of a compound can be calculated from the masses or percentages of the elements in a compound.
Students should be able to calculate empirical formulae and molecular formulae.

The mole concept (Oxford AQA International GCSE Chemistry)

a. The relative formula mass of a substance, in grams, is known as one mole of that substance.
Students should be able to use the relative formula mass of a substance to calculate the number of moles in a given mass of that substance and vice versa.
b. One mole contains 6.02 × 10²³ atoms or molecules. This number is known as Avogadro’s constant.

Using molar concentrations of solutions (Oxford AQA International GCSE Chemistry)

a. The concentration of a solution is related to the mass of the solute (in terms of number of moles) and the
volume of the solution. The concentration of a solution is calculated as follows:
Concentration (mol/dm³) = number of moles/volume of solution (in dm³).
b. The volumes of acid and alkali solutions that react with each other can be measured by titration using a suitable indicator.
Students should be able to carry out titrations using strong acids and strong alkalis only (sulfuric, hydrochloric and nitric acids only).
Required practical:
Establish the concentration of an unknown strong acid through titration with a strong base.
c. If the concentration of one of the reactants is known, the results of a titration can be used to find the concentration of the other reactant.
Students should know how to carry out a titration and be able to calculate the chemical quantities in titrations involving concentrations in mol/dm³ and in g/dm³.

d. The molar gas volume at room temperature and pressure is assumed to be 24 dm³
Students are expected to be able to calculate the number of moles or the volume of gas in a reaction
 

TRENDS WITHIN THE PERIODIC TABLE (Oxford AQA International GCSE Chemistry)

This section looks to both describe and explain trends within the periodic table along with more detailed knowledge and understanding of identified groups.

Group properties (Oxford AQA International GCSE Chemistry)

a. The elements in Group 1 of the periodic table (known as the alkali metals):
• are metals with low density (the first three elements in the group are less dense than water)
• react with non-metals to form ionic compounds in which the metal ion carries a charge of +1. The compounds are white solids that dissolve in water to form colourless solutions
• react with water, releasing hydrogen
• form hydroxides that dissolve in water to give alkaline solutions.
b. In Group 1, the further down the group an element is, the more reactive the element.
c. The elements in Group 7 of the periodic table (known as the halogens) react with metals to form ionic compounds in which the halide ion carries a charge of –1.
d. In Group 7, the further down the group an element is:
• the less reactive the element
• the higher its melting point and boiling point.
e. A more reactive halogen can displace a less reactive halogen from an aqueous solution of its salt.
f. The trends in reactivity within groups in the periodic table can be explained because the higher the energy level of the outer electrons:
• the more easily electrons are lost
• the less easily electrons are gained.
Students should be able to explain the relative reactivities of the elements in Group 1 and 7

TRANSITION METALS (Oxford AQA International GCSE Chemistry)
a. Transition metals are those in the centre of the periodic table between Groups 2 and 3. Many transition metals have ions with different charges, form coloured compounds and are useful as catalysts.
b. Compared with the elements in Group 1, transition metals:
• have higher melting points (except for mercury) and higher densities
• are stronger and harder
• are much less reactive and so do not react as vigorously with water or oxygen

THE RATE OF CHEMICAL CHANGE (Oxford AQA International GCSE Chemistry)

Rate of reaction (Oxford AQA International GCSE Chemistry)

a. The rate of a chemical reaction can be found by measuring the amount of a reactant used or the amount of product formed over time:
Rate of reaction = amount of reactant used / time
Rate of reaction = amount of product formed / time
Students need to be able to interpret graphs showing the amount of product formed (or reactant used up) with time, in terms of the rate of the reaction.
Knowledge of specific reactions other than those in the subject content is not required, but students will be expected to have studied examples of chemical reactions and processes in developing their skills during their study of this section.
b. Chemical reactions can occur only when reacting particles collide with each other and with sufficient energy. The minimum amount of energy that particles must have to react is called the activation energy.
c. Increasing the temperature increases the speed of the reacting particles so that they collide more frequently and more energetically. This increases the rate of reaction.
d. Increasing the pressure of reacting gases increases the frequency of collisions and so increases the rate of reaction.
e. Increasing the concentration of reactants in solutions increases the frequency of collisions and so increases the rate of reaction.
f. Increasing the surface area of solid reactants increases the frequency of collisions and so increases the rate of reaction.
Required practical:
Investigate factors affecting the rate of a reaction.
g. Catalysts change the rate of chemical reactions but are not used up during the reaction. Different reactions need different catalysts.
Knowledge of named catalysts other than those specified in the subject content is not required, but students should be aware of some examples of chemical reactions and processes that use catalysts.
h. Catalysts are important in increasing the rates of chemical reactions used in industrial processes to reduce costs

FACTORS AFFECTING EQUILIBRIUM (Oxford AQA International GCSE Chemistry)
a. When a reversible reaction occurs in a closed system, equilibrium is reached when the reactions occur at exactly the same rate in each direction.
b. The relative amounts of all the reacting substances at equilibrium depend on the conditions of the reaction.
c. If the temperature is raised:
• the yield from the endothermic reaction increases
• the yield from the exothermic reaction decreases.
If the temperature is lowered:
• the yield from the endothermic reaction decreases
• the yield from the exothermic reaction increases.
d. In gaseous reactions:
• an increase in pressure will favour the reaction that produces the least number of molecules as shown by the symbol equation for that reaction
• a decrease in pressure will favour the reaction that produces the greatest number of molecules as shown by the symbol equation for that reaction.
e. These factors, together with reaction rates, are important when determining the optimum conditions in industrial processes, including the Haber process.

PRODUCTION OF AMMONIA AND SULFURIC ACID (Oxford AQA International GCSE Chemistry)
a. The raw materials for the Haber process are nitrogen and hydrogen. Nitrogen is obtained from the air and hydrogen may be obtained from natural gas or other sources.
b. Ammonia is a raw material in the production of fertilizers.
Students should be able to explain the global need for fertilizers to maximise food yields.
c. The purified gases are passed over a catalyst of iron at a high temperature (about 450°C) and a high pressure (about 200 atmospheres). Some of the hydrogen and nitrogen react to form ammonia. The reaction is reversible so ammonia breaks down again into nitrogen and hydrogen:
nitrogen + hydrogen ? ammonia
On cooling, the ammonia liquefies and is removed. The remaining hydrogen and nitrogen are recycled.
d. Sulfuric acid is produced industrially using the contact process. It is a three–stage process, which incorporates a reversible process and the use of a catalyst.
Stage 1: Sulfur is burned in air to produce sulfur dioxide
S(s) + O₂(g) → SO₂(g)
Stage 2: Sulfur dioxide reacts with more oxygen to make sulfur trioxide
2SO₂(g) + O₂(g)  2SO₃(g)
This exothermic reaction is reversible and it requires a catalyst of Vanadium(V) oxide, V₂O₅, a temperature
of around 450 °C and atmospheric pressure

Stage 3: Sulfur trioxide reacts with water to make sulfuric acid
H₂O(l) + SO₃(g) → H₂SO₄(l or aq)
Students should be able to describe the stages in the contact process and also to explain why a catalyst, a high temperature and atmospheric pressure are used in Stage 2

REDOX REACTIONS (Oxford AQA International GCSE Chemistry)
a. Oxidation can be described as the gain of oxygen by a substance and reduction as the loss of oxygen from a substance.
b. Oxidation can also be described as the loss of electrons and reduction as gain of electrons.
Students should be able to describe chemical reactions within this specification in terms of oxidation and reduction using the definitions above.
c. When oxidation and reduction are happening at the same time this is known as a redox reaction, for example.

Fe₂O₃ + 3CO ==> 2Fe + 3CO₂

Iron(III) oxide is reduced (oxygen loss) and the carbon monoxide is oxidised (oxygen gain).

ENERGY CHANGES (Oxford AQA International GCSE Chemistry)

This section highlights that chemical reactions involve changes which require energy to make them happen. This is a fundamental concept which links to key ideas in biology and physics. The section also involves developing mathematical skills and also application of knowledge

Exothermic and endothermic reactions (Oxford AQA International GCSE Chemistry)

a. When chemical reactions occur, energy is transferred to or from the surroundings.
Knowledge of delta H (ΔH) conventions and enthalpy changes, including the use of positive values for endothermic reactions and negative values for exothermic reactions, is required.
b. An exothermic reaction is one that transfers energy to the surroundings. Examples of exothermic reactions include combustion, many oxidation reactions and neutralisation.
Students should be able to give examples of exothermic reactions including combustion, oxidation and neutralisation. Everyday uses of exothermic reactions include self-heating cans (eg for coffee) and hand warmers.
c. An endothermic reaction is one that takes in energy from the surroundings. Endothermic reactions include thermal decompositions. Some sports injury packs are based upon endothermic reactions.
d. In some chemical reactions, the products of the reaction can react to produce the original reactants. Such reactions are called reversible reactions and are represented as follows:
If A + B ==> C + D is exothermic, then C + D ==> A + B is endothermic
For example:

blue hydrated copper sulfate  == heat ==> white anhydrous copper sulfate + water (endothermic)
white anhydrous copper sulfate + water ==> blue hydrated copper sulfate (exothermic, mixture heats up)

Calculating and explaining energy change (Oxford AQA International GCSE Chemistry)

a. The relative amounts of energy released when substances burn can be measured by simple calorimetry, eg by heating water in a glass or metal container. This method can be used to compare the amount of energy produced by fuels.
Students should be able to calculate and compare the amount of energy released by different fuels given
the equation:  Q = mc ΔT
b. Energy is normally measured in joules (J) or kilojoules (kJ) for a given mass or amount of substance eg kilojoules per gram or kilojoules per mole.

c. The amount of energy produced by a chemical reaction in solution can be calculated from the measured temperature change of the solution when the reagents are mixed in an insulated container. This method can be used for reactions of solids with water or for neutralisation reactions.

d. Simple energy level diagrams can be used to show the relative energies of reactants and products, the activation energy and the overall energy change of a reaction.
Students will be expected to understand simple energy level diagrams showing the relative energies of reactants and products, the activation energy and the overall energy change, with a curved arrow to show the energy as the reaction proceeds.
Students should be able to relate these to exothermic and endothermic reactions.
e. During a chemical reaction:
• energy must be supplied to break bonds
• energy is released when bonds are formed.
Students should be able to calculate the energy transferred in reactions and interpret simple energy level diagrams in terms of bond breaking and bond formation (including the idea of activation energy and the effect on this of catalysts).
f. In an exothermic reaction, the energy released from forming new bonds is greater than the energy needed to break existing bonds.
Students should be able to calculate the energy transferred in reactions using bond dissociation energies
supplied.
g. In an endothermic reaction, the energy needed to break existing bonds is greater than the energy released from forming new bonds.
h. Catalysts provide a different pathway for a chemical reaction that has a lower activation energy.
Students should be able to represent the effect of a catalyst on an energy level diagram

CHEMICAL CELLS AND FUEL CELLS (Oxford AQA International GCSE Chemistry)
a. A chemical cell produces a potential difference until the reactants are used up.
b. Fuel cells produce electricity through the reaction of a fuel with oxygen. Hydrogen-oxygen fuel cells use hydrogen as their fuel, and are useful in cars and spacecraft. Water is the only waste product from a hydrogen–oxygen fuel cell, so they cause less pollution when in use.
Students should be able to compare the advantages and disadvantages of the combustion of hydrogen with the use of hydrogen fuel cells from information that is provided.
Students should know and understand the benefits and disadvantages of hydrogen fuel in terms of:
• storage and use
• products of combustion.
Knowledge of the details of the reactions in fuel cells is not required.

ORGANIC CHEMISTRY (Oxford AQA International GCSE Chemistry)

Carbon compounds as fuels (Oxford AQA International GCSE Chemistry)

Crude oil (Oxford AQA International GCSE Chemistry)

a. Crude oil is a mixture of a very large number of compounds.
b. Most of the compounds in crude oil are hydrocarbons, which are molecules made up of hydrogen and carbon atoms only.
c. The many hydrocarbons in crude oil may be separated into fractions, each of which contains molecules with a similar number of carbon atoms, by evaporating the oil and allowing it to condense at a number of different temperatures. This process is called fractional distillation.
Students should know and understand the main processes in continuous fractional distillation in a fractionating column.
Knowledge of the names of specific fractions or fuels is not required

Hydrocarbons (Oxford AQA International GCSE Chemistry)

a. Most of the hydrocarbons in crude oil are saturated hydrocarbons called alkanes. The general formula for the homologous series of alkanes is C_nH_2n+2
Students should know that in saturated hydrocarbons all the carbon–carbon bonds are single covalent
bonds.
b. Alkane molecules can be represented in the following forms:
C₂H₆   or   
Students should know that in displayed structures represents a covalent bond.
Students should be able to recognise alkanes from their formulae in any of the forms, but do not need to know the names of specific alkanes other than methane, ethane and propane.
c. Some properties of hydrocarbons depend on the size of their molecules. These properties influence how hydrocarbons are used as fuels.
Knowledge and understanding of trends in properties of hydrocarbons is limited to:
• boiling points,  viscosity  and  flammability.
d. Most fuels, including coal, contain carbon and/or hydrogen and may also contain some sulfur. The gases released into the atmosphere when a fuel burns may include carbon dioxide, water (vapour), carbon monoxide, sulfur dioxide and oxides of nitrogen. Solid particles (particulates) may also be released. Solid particles may contain soot (carbon) and unburnt fuels.
Sulfur dioxide and oxides of nitrogen cause acid rain, an increase in carbon dioxide may result in climate change, and solid particles cause global dimming

Students should be able to relate products of combustion to the elements present in compounds in the fuel and to the extent of combustion (whether complete or incomplete).
No details of how the oxides of nitrogen are formed are required, other than the fact that they are formed at high temperatures.
e. The combustion of hydrocarbon fuels releases energy. During combustion, the carbon and hydrogen in the fuels are oxidised.

f. Ethanol can be made by reacting ethene with steam:
C₂H₄ + H₂O → C₂H₅OH
Phosphoric acid is used as a catalyst to increase the rate of the reaction.
This is efficient because it is a continuous process. However, ethene is derived from crude oil, a non-renewable resource which may run out one day.
Ethanol can also be made by fermenting sugar:
C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂
Enzymes in yeast are natural catalysts for this reaction, and this is a batch process. Unlike ethene, sugar is a renewable resource.
Students should be able to compare the two ways of making ethanol in terms of type of raw material, type of process, labour, rate of reaction, conditions needed, purity of product and energy requirements
g. Biofuels, including biodiesel and ethanol, are produced from plant material, and are possible alternatives to hydrocarbon fuels.
Students should know and understand the benefits and disadvantages of biofuels in terms of:
• use of renewable resources
• their impacts on land use
• their carbon footprint.
Students should know that ethanol for use as a biofuel is produced from a dilute solution of ethanol obtained by the fermentation of plant materials at a temperature between 20 °C and 35 °C. Detailed knowledge of the methods used to produce other biofuels is not required.

Obtaining useful substances from crude oil (Oxford AQA International GCSE Chemistry)

a. Hydrocarbons can be broken down (cracked) to produce smaller, more useful molecules. This process involves heating the hydrocarbons to vaporise them. The vapours are either passed over a hot catalyst or mixed with steam and heated to a very high temperature so that thermal decomposition reactions then occur.
b. The products of cracking include alkanes and unsaturated hydrocarbons called alkenes. The general formula for the homologous series of alkenes is C_nH_2n
Students should know that in unsaturated hydrocarbons some of the carbon–carbon bonds are double covalent bonds.

Required practical:
Test for the presence of a double bond in an unknown hydrocarbon.

c. Unsaturated hydrocarbon molecules can be represented in the following forms:
C₃H₆   or  
Students should know that in displayed structures represents a double bond.
Students should be able to recognise alkenes from their names or formulae, but do not need to know the names of individual alkenes other than ethene and propene.
d. Alkenes react with bromine water, turning it from orange to colourless.
e. Some of the products of cracking are useful as fuels

Synthetic and naturally occurring polymers (Oxford AQA International GCSE Chemistry)

a. Alkenes can be used to make polymers such as poly(ethene) and poly(propene). In polymerisation reactions, many small molecules (monomers) join together to form very large molecules (polymers).
For example - the formation of the polymer poly(ethene) from the monomer ethene

Students should be able to recognise the molecules involved in these reactions in the forms shown in the subject content. They should be able to represent the formation of a polymer from a given alkene monomer.
Further details of polymerisation are not required.
b. The properties of polymers depend on what they are made from and the conditions under which they are made. For example, low-density (LD) and high-density (HD) poly(ethene) are produced using different catalysts and reaction conditions.
c. Thermosoftening polymers consist of individual, tangled polymer chains. Thermosetting polymers consist of polymer chains with cross-links between them so that they do not melt when they are heated.
Extension Tier students should be able to explain thermosoftening polymers in terms of intermolecular forces.
d. Polymers have many useful applications and new uses are being developed. Examples include: new packaging materials, waterproof coatings for fabrics, dental polymers, wound dressings, hydrogels, and smart materials (including shape memory polymers).
Students should consider the ways in which new materials are being developed and used, but will not need to recall the names of specific examples.
e. Many polymers are not biodegradable, ie they are not broken down by microbes. This can lead to problems with waste disposal.

Knowledge of specific named examples is not required, but students should be aware of the problems that are caused in landfill sites and in litter.
f. Plastic bags are being made from polymers and cornstarch so that they break down more easily. Biodegradable plastics made from cornstarch have been developed

Organic compounds – their structure and reactions

Alcohols

a. Alcohols contain the functional group –OH. Methanol, ethanol and propanol are the first three members of a homologous series of alcohols. Alcohols can be represented in the following forms:
CH₃CH₂OH   or  
Students should be able to recognise alcohols from their names or formulae, but do not need to know the names of individual alcohols other than methanol, ethanol and propanol.
b. Methanol, ethanol and propanol:
• dissolve in water to form a neutral solution
• react with sodium to produce hydrogen
• burn in air
• are used as fuels and solvents, and ethanol is the main alcohol in alcoholic drinks.
c. Ethanol can be oxidised to ethanoic acid, (a carboxylic acid) either by chemical oxidising agents or by microbial action. Ethanoic acid is the main acid in vinegar.

Carboxylic acids

a. Ethanoic acid is a member of the homologous series of carboxylic acids, which have the functional group –COOH. The structures of carboxylic acids can be represented in the following forms:
CH₃COOH   or  
Students should be able to recognise carboxylic acids from their names or formulae, but do not need to know the names of individual carboxylic acids other than methanoic acid, ethanoic acid and propanoic acid.
b. Carboxylic acids:
• dissolve in water to produce acidic solutions
• react with carbonates to produce carbon dioxide
• react with alcohols in the presence of an acid catalyst to produce esters
• do not ionise completely when dissolved in water and so are weak acids
• aqueous solutions of weak acids have a higher pH value than aqueous solutions of strong acids with the same concentration.
Students are expected to write balanced chemical equations for the reactions of carboxylic acids

Esters
a. Esters have the functional group –COO–. The structures of esters can be represented in the following forms:
CH₃COOCH₂CH₃    or  
Students will not be expected to give the names of esters other than ethyl ethanoate, but should be able to recognise a compound as an ester from its name or its structural formula.
Ethyl ethanoate is the ester produced from ethanol and ethanoic acid (its a reversible reaction).

ethanoic acid + ethanol ethyl ethanoate + water

+ + H₂O

sometimes more simply written as

CH₃COOH + CH₃CH₂OH CH₃COOCH₂CH₃ + H₂O

b. Esters are volatile compounds with distinctive smells and are used as flavourings and perfumes

The exam PERIODIC TABLE (Oxford AQA International GCSE Chemistry)