Revision summary help for the 9-1 AQA GCSE Combined Science Trilogy 2nd chemistry paper learning objectives for

AQA GCSE science 8464/C/2F and 8464/C/2H 2020 exam paper onwards (re-edit)

AQA GCSE Grade 9-1 Combined Science Trilogy chemistry 8464 Paper 4 Chemistry 2 2F 2H papers - Combined Science TRILOGY chemistry paper 2 Topic 13 "The rate and extent of chemical change", Topic 14 "Organic chemistry", Topic 15 "Chemical analysis", Topic 16 "Chemistry f the atmosphere", Topic 17 "Using resources"

LINK for AQA 9-1 GCSE Combined Science Trilogy chemistry paper 1

LINK for AQA 9-1 GCSE CHEMISTRY 1 paper 1

LINK for AQA 9-1 GCSE CHEMISTRY 2 paper 2

GCSE Chemistry Revision notes

 For ALL other exam papers, use and bookmark the link below

INDEX for all links

PLEASE READ CAREFULLY THE FOLLOWING POINTS before using my AQA 9-1 GCSE science pages

1. ALL my unofficial GCSE (Grade 9-1) revision help summaries are based on the NEW 2016 official AQA (Grade 9-1) GCSE CHEMISTRY/combined science trilogy chemistry specifications.

2. Make sure you know whether you are doing separate science AQA GCSE grade 9-1 CHEMISTRY OR AQA GCSE grade 9-1 Combined Science Trilogy chemistry and double check your exam table from school, college or academy.

3. Also, make sure you know whether you are entered for a higher tier (HT) or a foundation tier (FT) AQA GCSE science-chemistry course, so watch out for the (HT only) 'markers'.

4. I hope my revision pages help as you get to know my website, its very big and not always easy to navigate, but it is no substitute for making good lesson notes, trying your best on homework questions, studying your textbook, doing past papers of AQA GCSE combined science/chemistry for exam question practice and, above all, attentive to your teacher's teaching!

5. I know from feedback that my gcse science summary revision pages have proved useful but they do not guarantee a high grade, that all depends on you and the factors mentioned in point 4. above. Please note that my GCSE science revision pages are designed to be used for online convenience, so, beware, printouts could be quite long!
6. It is really important that YOU cross-check, from my web pages, the learning objectives from the syllabus-specification with YOUR own lesson/revision notes and textbooks for YOUR AQA GCSE 9-1 combined science trilogy chemistry course.
7. If you think there is any ERROR in my multiple choice chemistry quizzes PLEASE EMAIL me the URL quiz link and quote the reference number in square brackets at the end of the question e.g. [xx-yy]. Some quizzes, particularly the compilations, are quite large and take some time to download.

8. 'Doc b's chemistry' is a big website so the Google [SEARCH] box at the bottom of each index or revision notes page can be VERY USEFUL - sometimes its better than the indexes for finding things!

9. Links to specific GCSE chemistry notes and quizzes about the topic in question have been added, and from these pages, you may find other links to more useful material linked to the topic.

10. When it comes to the final exam papers, at that point, YOU ARE THEN RESPONSIBLE FOR THE GRADE YOU ACHIEVE, not your teachers or me or my website (which isn't perfect!), so make sure you are properly prepared!

11. If there is anything about the website you are unhappy with, or you think there is an error, or you think something hasn't been covered adequately, please politely email me with your query to chem55555@hotmail.com

12. NOTE on grades: Foundation Tier FT grades 1 to 5  and  Higher Tier HT grades 4 to 9. In terms of old grades the following is an approximate comparison: grades 7-9 (A-A*), 4-6 (C-B), 1-3 (G-D), U (U) (from OFQUAL Jan 2018)

Syllabus-specification CONTENT INDEX of revision summary notes

Revision summaries for  AQA GCSE Combined Science Trilogy Chemistry Paper 1 (separate page)

What's assessed in this paper?

SUMMARY Topic 1/8 Atomic structure and the periodic table  (Comb. Sci. Trilogy Chemistry paper 1)

SUMMARY Topic 2/9 Bonding, structure, and the properties of matter  (Comb. Science Trilogy paper 1)

SUMMARY Topic 3/10 Quantitative chemistry  (AQA GCSE Combined Sci. Trilogy Chemistry paper 1)

SUMMARY Topic 4/11 Chemical changes  (AQA GCSE Combined Science Trilogy Chemistry paper 1)

SUMMARY Topic 5/12 Energy changes  (AQA GCSE Combined Science Trilogy Chemistry paper 1)

Revision summaries for AQA 9-1 GCSE Combined Science: Chemistry Paper 2 (this page)

What's assessed in this paper?    (the 'sub-topic' numbers are just based on a simple numerical order)

SUMMARY Topic 6/13 The rate and extent of chemical change (Comb. Sci. Trilogy Chemistry paper 2)

Topic 6.1 Rate of reaction

Topic 6.2 Reversible reactions and dynamic equilibrium

SUMMARY Topic 7/14 Organic chemistry   (AQA GCSE Combined Science Trilogy Chemistry paper 2)

Topic 7.1 Carbon compounds as fuels and feedstock

SUMMARY Topic 8/15 Chemical analysis   (AQA GCSE Combined Science Trilogy Chemistry paper 2)

Topic 8.1 Purity, formulations and chromatography

Topic 8.2 Identification of common gases
 

SUMMARY Topic 9/16 Chemistry of the atmosphere   (AQA GCSE Comb. Sci. Trilogy Chemistry paper 2)

Topic 9.1 The composition and evolution of the Earth's atmosphere

Topic 9.2 Carbon dioxide and methane as greenhouse gases

Topic 9.3 Common atmospheric pollutants and their sources

SUMMARY Topic 10/17 Using resources   (AQA GCSE Comb. Sci. Trilogy Chemistry paper 2 chemistry 2)

Topic 10.1 Using the Earth's resources and obtaining potable water

Topic 10.2 Life cycle assessment and recycling

SUBJECT CONTENT of the syllabus-specification:

TOPICS for AQA 9-1 GCSE Combined Science Trilogy Chemistry Paper 2

A page of important ideas, concepts and definitions for chemistry students

Topic 13 The rate and extent of chemical change

(revision notes summary for AQA 9-1 GCSE Combined Science Trilogy: Chemistry Paper 4, Topic 13 "The rate and extent of chemical change")

Appreciate that chemical reactions can occur at vastly different rates. Whilst the reactivity of chemicals is a significant factor in how fast chemical reactions proceed, there are many variables that can be manipulated in order to speed them up or slow them down. Chemical reactions may also be reversible and therefore the effect of different variables needs to be established in order to identify how to maximise the yield of desired product. Understanding energy changes that accompany chemical reactions is important for this process. In industry, chemists and chemical engineers determine the effect of different variables on reaction rate and yield of product. Whilst there may be compromises to be made, they carry out optimisation processes to ensure that enough product is produced within a sufficient time, and in an energy efficient way.

AQA GCSE (Grade 9-1) GCSE combined science trilogy Topic 13 The rate and extent of chemical change quiz content: Factors affecting the rate of a chemical reaction - temperature, concentration, particle size, catalysts etc., reversible reactions, chemical equilibrium, effect of changes in conditions on the position of an equilibrium (HT only)

Topic 13 The rate and extent of chemical change QUIZ (AQA Combined Science Trilogy)

HT = higher tier (harder - usually more theory & depth) and FT = foundation tier (easier) 

6.1 Rate of reaction

(revision notes summary for AQA 9-1 GCSE Combined Science Trilogy: Chemistry Paper 4, Topic 13 "The rate and extent of chemical change")

6.1.1 Calculating rates of reactions

Know the rate of a chemical reaction can be found by measuring the quantity of a reactant used or the quantity of product formed over time:

mean rate of reaction = quantity of reactant used / time taken

mean rate of reaction = quantity of product formed / time taken

The quantity of reactant or product can be measured by the mass in grams or by a volume in cm³. The units of rate of reaction may be given as g/s or cm³/s.

For the Higher Tier, you are also required to use quantity of reactants in terms of moles and units for rate of reaction in mol/s.

You should be able to:

calculate the mean rate of a reaction from given information about the quantity of a reactant used or the quantity of a product formed and the time taken

draw, and interpret, graphs showing the quantity of product formed or quantity of reactant used up against time

draw tangents to the curves on these graphs and use the slope of the tangent as a measure of the rate of reaction

(HT only) calculate the gradient of a tangent to the curve on these graphs as a measure of rate of reaction at a specific time.

In the context of rates of reaction data, you must be able to

Recognise and use expressions in decimal form.

Use ratios, fractions and percentages.

Make estimates of the results of simple calculations.

Translate information between graphical and numeric form.

Plot two variables from experimental or other data.

Determine the slope and intercept of a linear graph. Draw and use the slope of a tangent to a curve as a measure of rate of change.

What do we mean by the rate/speed of reaction? how can we measure it? Revision Notes

Examples of graphs of rate data, interpretation  Revision Notes

6.1.2 Factors which affect the rates of chemical reactions

Factors which affect the rates of chemical reactions include:

the concentrations of reactants in solution

the pressure of reacting gases

the surface area of solid reactants

the temperature

and the presence of catalysts.

You should be able to recall how changing these factors affects the rate of chemical reactions.

Required practical 5: You should have investigated how changes in concentration affect the rates of reactions by a method involving measuring the volume of a gas produced and a method involving a change in colour or turbidity ('cloudiness'!).

Particle model of the collision theory of chemical reaction rate factors Revision Notes

Effect of changing reactant concentration in solution Revision Notes

Effect of changing pressure in reacting gases Revision Notes

Effect of changing particle size/surface area & stirring of a solid reactant Revision Notes

Effect of changing the temperature of reactants Revision Notes

Effect of using a catalyst in a chemical reaction Revision Notes

Multiple choice Quiz on the Rates of Chemical Reactions

Crossword on Rates of Reactions * Answers

Wordfill worksheet on Rates of Chemical Reactions

(1) matching pair quizzes on Rates of Chemical Reactions and (2)

2nd Word-fill quiz "What factors Affect the Speed of a Chemical reaction?"

6.1.3 Collision theory and activation energy

(revision notes summary for AQA 9-1 GCSE Combined Science Trilogy: Chemistry Paper 4, Topic 13 "The rate and extent of chemical change")

You should understand that collision theory explains how various factors affect rates of reactions. According to this theory, 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.

Know that increasing the concentration of reactants in solution, the pressure of reacting gases, and the surface area of solid reactants increases the frequency of collisions and so increases the rate of reaction. Increasing the temperature increases the frequency of collisions and makes the collisions more energetic, and so increases the rate of reaction.

You should be able to:

predict and explain using collision theory the effects of changing conditions of concentration, pressure and temperature on the rate of a reaction

predict and explain the effects of changes in the size of pieces of a reacting solid in terms of surface area to volume ratio

use simple ideas about proportionality when using collision theory to explain the effect of a factor on the rate of a reaction

Particle model of the collision theory of chemical reaction rate factors Revision Notes

Activation energy and reaction profiles Revision Notes

6.1.4 Catalysts

Know that catalysts change the rate of chemical reactions but are not used up during the reaction.

Different reactions need different catalysts.

Enzymes act as catalysts in biological systems.

Catalysts increase the rate of reaction by providing a different pathway for the reaction that has a lower activation energy.

Know how to draw a reaction profile for a catalysed reaction.

You should be able to identify catalysts in reactions from their effect on the rate of reaction and because they are not included in the chemical equation for the reaction.

You should be able to explain catalytic action in terms of activation energy.

You do not need to know the names of catalysts other than those specified in the subject content.

Effect of using a catalyst in a chemical reaction Revision Notes

Activation energy and reaction profiles, catalysts and activation energy Revision Notes

Index of topics for AQA Combined Science Trilogy Chemistry paper 1 and paper 2

6.2 Reversible reactions and dynamic equilibrium  

(revision notes summary for AQA 9-1 GCSE Combined Science Trilogy: Chemistry Paper 4, Topic 13 "The rate and extent of chemical change")

Topic 13 The rate and extent of chemical change QUIZ (AQA Combined Science Trilogy)

6.2.1 Reversible reactions

Know that 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: A + B C + D

The direction of reversible reactions can be changed by changing the conditions eg

Ammonium chloride + heat ammonia + hydrogen chloride

NH₄Cl_(s) NH_3(g) + HCl_(g)  and the thermal decomposition is reversed on cooling

Reversible Reactions Revision Notes

6.2.2 Energy changes and reversible reactions

Know that if a reversible reaction is exothermic in one direction, it is endothermic in the opposite direction. The same amount of energy is transferred in each case. For example:

blue hydrated copper(II) sulphate + heat white anhydrous copper(II) sulphate + water

CuSO₄.5H₂O_(s) CuSO_4(s) + 5H₂O_(g)   and the reaction reversed on cooling

The dehydration decomposition to give the white solid is the forward endothermic reaction and the 're-hydration' to reform the blue crystals is the backward exothermic reaction.

Reversible Reactions - experiments described and explained Revision Notes

6.2.3 Equilibrium

Understand and know that when a reversible reaction occurs in apparatus which prevents the escape of reactants and products, equilibrium is reached when the forward and reverse reactions occur at exactly the same rate.

6.2.4 The effect of changing conditions on equilibrium (HT only)

Know that the relative amounts of all the reactants and products at equilibrium depend on the conditions of the reaction.

If a system is at equilibrium and a change is made to any of the conditions, then the system responds to counteract the change.

The effects of changing conditions on a system at equilibrium can be predicted using Le Chatelier’s Principle.

You should be able to make qualitative predictions about the effect of changes on systems at equilibrium when given appropriate information.

Reversible Reactions - experiments described and explained Revision Notes

Reversible reactions and chemical equilibrium (including Le Chatelier's Principle rules) Revision Notes

6.2.5 The effect of changing concentration (HT only)

Know that if the concentration of one of the reactants or products is changed, the system is no longer at equilibrium and the concentrations of all the substances will change until equilibrium is reached again.

If the concentration of a reactant is increased, more products will be formed until equilibrium is reached again.

If the concentration of a product is decreased, more reactants will react until equilibrium is reached again.

You should be able to interpret appropriate given data to predict the effect of a change in concentration of a reactant or product on given reactions at equilibrium.

Reversible reactions and chemical equilibrium (including Le Chatelier's Principle rules) Revision Notes

6.2.6 The effect of temperature changes on equilibrium (HT only)

If the temperature of a system at equilibrium is increased:

the relative amount of products at equilibrium increases for an endothermic reaction

the relative amount of products at equilibrium decreases for an exothermic reaction.

If the temperature of a system at equilibrium is decreased:

the relative amount of products at equilibrium decreases for an endothermic reaction

the relative amount of products at equilibrium increases for an exothermic reaction.

You should be able to interpret appropriate given data to predict the effect of a change in temperature on given reactions at equilibrium.

Reversible reactions and chemical equilibrium (including Le Chatelier's Principle rules) Revision Notes

6.2.7 The effect of pressure changes on equilibrium (HT only)

Know that for a gaseous reactions at equilibrium:

an increase in pressure causes the equilibrium position to shift towards the side with the smaller number of molecules as shown by the symbol equation for that reaction

a decrease in pressure causes the equilibrium position to shift towards the side with the larger number of molecules as shown by the symbol equation for that reaction.

You should be able to interpret appropriate given data to predict the effect of pressure changes on given reactions at equilibrium.

Reversible reactions and chemical equilibrium (including Le Chatelier's Principle rules) Revision Notes

NEW QUIZ Combined QUIZ on rates of reaction, reversible reactions and equilibrium - Le Chatelier's Rules

Index of topics for AQA Combined Science Trilogy Chemistry paper 1 and paper 2

Topic 14 Organic chemistry  

(revision notes summary for AQA 9-1 GCSE Combined Science Trilogy: Chemistry Paper 4, Topic 14 "Organic chemistry")

Appreciate that the chemistry of carbon compounds is so important that it forms a separate branch of chemistry. A great variety of carbon compounds is possible because carbon atoms can form chains and rings linked by C-C bonds. This branch of chemistry gets its name from the fact that the main sources of organic compounds are living, or once-living materials from plants and animals. These sources include fossil fuels which are a major source of feedstock for the petrochemical industry. Chemists are able to take organic molecules and modify them in many ways to make new and useful materials such as polymers, pharmaceuticals, perfumes and flavourings, dyes and detergents.

AQA GCSE (Grade 9-1) GCSE combined science trilogy chemistry Topic 14 Organic chemistry quiz content: oil, fractional distillation, properties and uses of hydrocarbons, alkanes, cracking and alkenes, need Qs on alcohols and carboxylic acids

Topic 14 Organic Chemistry QUIZ (AQA GCSE Combined Science Trilogy Chemistry)

HT = higher tier (harder - usually more theory & depth) and FT = foundation tier (easier) 

7.1 Carbon compounds as fuels and feedstock

Multiple choice QUIZ on Oil Products - hydrocarbon chemistry (best done when 7.1.1 to 7.2.2 completed)

7.1.1 Crude oil, hydrocarbons and alkanes

Know that crude oil is a finite resource found in rocks. Crude oil is the remains of an ancient biomass consisting mainly of plankton that was buried in mud.

Crude oil is a mixture of a very large number of compounds. Most of the compounds in crude oil are hydrocarbons, which are molecules made up of hydrogen and carbon atoms only. Most of the hydrocarbons in crude oil are hydrocarbons called alkanes. The general formula for the homologous series of alkanes is C_nH_2n+2 The first four members of the alkanes are methane, ethane, propane and butane. Alkane molecules can be represented in the following forms: C₂H₆ or

You should be able to recognise substances as alkanes given their formulae in these forms.

You do not need to know the names of specific alkanes other than methane, ethane, propane and butane.

Alkanes - saturated hydrocarbons, structure and reactions including combustion Revision Notes

Fractional distillation of crude oil & molecular properties related to uses of fractions Revision Notes

7.1.2 Fractional distillation and petrochemicals

(revision notes summary for AQA 9-1 GCSE Combined Science Trilogy: Chemistry Paper 4, Topic 14 "Organic chemistry")

Know 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 different temperatures. This process is called fractional distillation.

The fractions can be processed to produce fuels and feedstock for the petrochemical industry.

Many of the fuels on which we depend for our modern lifestyle, such as petrol, diesel oil, kerosene, heavy fuel oil and liquefied petroleum gases, are produced from crude oil.

Many useful materials on which modern life depends are produced by the petrochemical industry, such as solvents, lubricants, polymers, detergents.

The vast array of natural and synthetic carbon compounds occur due to the ability of carbon atoms to form families of similar compounds.

You should be able to explain the separation of crude oil by fractional distillation.

Knowledge of the names of other specific fractions or fuels is not required.

Fractional distillation of crude oil & uses of fractions Revision Notes

multiple choice QUIZ on Oil Products

3 linked easy Oil Products gap-fill quiz worksheets

Word-fill quiz "Origin of Crude Oil" *

Word-fill quiz "Crude Oil and its Fractional distillation"

Word-fill quiz "Getting products from crude oil"

Word-fill quiz "The Uses of the Fractions from Crude Oil"

7.1.3 Properties of hydrocarbons

Know that some properties of hydrocarbons depend on the size of their molecules, including boiling point and viscosity which increase with increasing molecular size and flammability which decreases with increasing molecular size. These properties influence how hydrocarbons are used as fuels.

Knowledge of trends in properties of hydrocarbons is limited to: boiling points, viscosity and flammability.

You should be able to recall how boiling point, viscosity and flammability change with increasing molecular size.

The combustion of hydrocarbon fuels releases energy. During combustion, the carbon and hydrogen in the fuels are oxidised. The complete combustion of a hydrocarbon produces carbon dioxide and water.

You should be able to write balanced equations for the complete combustion of hydrocarbons with a given formula.

Alkanes - saturated hydrocarbons, structure and reactions including combustion Revision Notes

Alkenes - unsaturated hydrocarbons, physical and chemical properties

multiple choice QUIZ on Oil Products

Word-fill quiz "More on hydrocarbon molecules"

7.1.4 Cracking and alkenes

Know that hydrocarbons can be broken down (cracked) to produce smaller, more useful molecules.

Cracking can be done by various methods including catalytic cracking and steam cracking.

You should be able to describe in general terms the conditions used for catalytic cracking and steam cracking. The products of cracking include alkanes and another type of hydrocarbon called alkenes.

Alkenes are more reactive than alkanes and react with bromine water, which is used as a test for alkenes.

You should be able to recall the colour change when bromine water reacts with an alkene.

There is a high demand for fuels with small molecules and so some of the products of cracking are useful as fuels.

Alkenes are used to produce polymers and as starting materials for the production of many other chemicals.

You should be able to balance chemical equations as examples of cracking given the formulae of the reactants and products.

You should be able to give examples to illustrate the usefulness of cracking and also be able to explain how modern life depends on the uses of hydrocarbons.

You do not need to know the formulae or names of individual alkenes.

Alkenes - unsaturated hydrocarbons - structure and reactions Revision Notes

Cracking - a problem of supply and demand, other products Revision Notes

multiple choice QUIZ on Oil Products

Word-fill quiz "Cracking Oil to make Alkanes and Alkenes"

Word-fill quiz "Cracking oil fractions and uses of products"

Word-fill quiz "Cracking, fuels and polymers"

Word-fill quiz "More on uses of products from cracking"

Index of topics for AQA Combined Science Trilogy Chemistry paper 1 and paper 2

Topic 15 Chemical analysis  

(revision notes summary for AQA 9-1 GCSE Combined Science Trilogy: Chemistry Paper 4, Topic 15 "Chemical analysis")

Appreciate that analysts have developed a range of qualitative tests to detect specific chemicals. The tests are based on reactions that produce a gas with distinctive properties, or a colour change or an insoluble solid that appears as a precipitate. Instrumental methods provide fast, sensitive and accurate means of analysing chemicals, and are particularly useful when the amount of chemical being analysed is small. Forensic scientists and drug control scientists rely on such instrumental methods in their work.

AQA GCSE (Grade 9-1) GCSE Combined Science Trilogy chemistry Topic 15 Chemical analysis quiz content: identifying common gases, testing for positive ions (cations), testing for negative ions (anions), flame tests, metal hydroxides, carbonates, halides, sulfates, need questions on purity, formulations, flame emission spectroscopy, chromatography, instrumental methods of analysis

Topic 15 Chemical analysis QUIZ (AQA GCSE Combined Science Trilogy Chemistry)

HT = higher tier (harder - usually more theory & depth) and FT = foundation tier (easier) 

8.1 Purity, formulations and chromatography

(revision notes summary for AQA 9-1 GCSE Combined Science Trilogy: Chemistry Paper 4, Topic 15 "Chemical analysis")

8.1.1 Pure substances

Know that in chemistry, a pure substance is a single element or compound, not mixed with any other substance.

Pure elements and compounds melt and boil at specific temperatures. Melting point and boiling point data can be used to distinguish pure substances from mixtures.

In everyday language, a pure substance can mean a substance that has had nothing added to it, so it is unadulterated and in its natural state, eg pure milk.

You should be able to use melting point and boiling point data to distinguish pure from impure substances.

Definitions in Chemistry eg atom, molecule, formula, element, compound, mixture, pure, impure - criteria tests

8.1.2 Formulations

A formulation is a mixture that has been designed as a useful product. Many products are complex mixtures in which each chemical has a particular purpose. Formulations are made by mixing the components in carefully measured quantities to ensure that the product has the required properties. Formulations include fuels, cleaning agents, paints, medicines, alloys, fertilisers and foods.

You should be able to identify formulations given appropriate information but you do not need to know the names of components in proprietary products.

Introduction to formulations and examples explained Revision Notes

8.1.3 Chromatography

Know that chromatography can be used to separate mixtures and can give information to help identify substances. Chromatography involves a stationary phase and a mobile phase. Separation depends on the distribution of substances between the phases.

In paper chromatography a solvent moves through the paper carrying different compounds different distances, depending on their attraction for the paper and the solvent. The ratio of the distance moved by a compound (centre of spot from origin) to the distance moved by the solvent can be expressed as its R_f value:

R_f = distance moved by substance  ÷  distance moved by solvent

Different compounds have different R_f values in different solvents, which can be used to help identify the compounds.

The compounds in a mixture may separate into different spots depending on the solvent but a pure compound will produce a single spot in all solvents.

You should be able to:

explain how paper chromatography separates mixtures

suggest how chromatographic methods can be used for distinguishing pure substances from impure substances

interpret chromatograms and determine R_f values from chromatograms.

In the context of chromatography, be able to:

recognise and use expressions in decimal form,

use ratios, fractions and percentages,

make estimates of the results of simple calculations,

use an appropriate number of significant figures.

Required practical 6: You should have investigated how paper chromatography can be used to separate and tell the difference between coloured substances and calculated R_f values.

Paper chromatography Revision Notes

Index of topics for AQA Combined Science Trilogy Chemistry paper 1 and paper 2

8.2 Identification of common gases

(revision notes summary for AQA 9-1 GCSE Combined Science Trilogy: Chemistry Paper 4, Topic 15 "Chemical analysis")

Topic 15 Chemical analysis QUIZ (AQA GCSE Combined Science Trilogy Chemistry)

Test for hydrogen   The test for hydrogen uses a burning splint held at the open end of a test tube of the gas. Hydrogen burns rapidly with a pop sound.

Test for oxygen   The test for oxygen uses a glowing splint inserted into a test tube of the gas. The splint relights in oxygen.

Test for carbon dioxide   The test for carbon dioxide uses an aqueous solution of calcium hydroxide (lime water). When carbon dioxide is shaken with or bubbled through limewater the limewater turns milky (cloudy).

Test for chlorine   The test for chlorine uses litmus paper. When damp litmus paper is put into chlorine gas the litmus paper is bleached and turns white.

Summary of 'GCSE' tests for gases and ions

Quiz on Qualitative Analysis - chemical test methods and deductions from results

Index of topics for AQA Combined Science Trilogy Chemistry paper 1 and paper 2

Topic 16 Chemistry of the atmosphere  

(revision notes summary for AQA 9-1 GCSE Combined Science Trilogy: Chemistry Paper 4, Topic 16 "Chemistry of the atmosphere")

The Earth’s atmosphere is dynamic and forever changing. The causes of these changes are sometimes man-made and sometimes part of many natural cycles. Scientists use very complex software to predict weather and climate change as there are many variables that can influence this. The problems caused by increased levels of air pollutants require scientists and engineers to develop solutions that help to reduce the impact of human activity.

HT = higher tier (harder - usually more theory & depth) and FT = foundation tier (easier)

9.1 The composition and evolution of the Earth's atmosphere

(revision notes summary for AQA 9-1 GCSE Combined Science Trilogy: Chemistry Paper 4, Topic 16 "Chemistry of the atmosphere")

9.1.1 The proportions of different gases in the atmosphere

Know that for 200 million years, the proportions of different gases in the atmosphere have been much the same as they are today: about four-fifths (approximately 80%) nitrogen, about one-fifth (approximately 20%) oxygen and small proportions of various other gases, including carbon dioxide, water vapour and noble gases. Be able to use ratios, fractions and percentages.

Our atmosphere - composition, determining % oxygen, uses of gases in air Revision Notes

Word-fill quiz "The Earth's Atmosphere"

Word-fill quiz "The Composition of the Earth's Atmosphere"

9.1.2 The Earth's early atmosphere

Appreciate that the theories about what was in the Earth’s early atmosphere and how the atmosphere was formed have changed and developed over time. Evidence for the early atmosphere is limited because of the time scale of 4.6 billion years.

One theory suggests that during the first billion years of the Earth’s existence there was intense volcanic activity that released gases that formed the early atmosphere and water vapour that condensed to form the oceans.

At the start of this period the Earth’s atmosphere may have been like the atmospheres of Mars and Venus today, consisting of mainly carbon dioxide with little or no oxygen gas.

Volcanoes also produced nitrogen which gradually built up in the atmosphere and there may have been small proportions of methane and ammonia. When the oceans formed carbon dioxide dissolved in the water and carbonates were precipitated producing sediments, reducing the amount of carbon dioxide in the atmosphere.

No knowledge of other theories is required but you should be able to, given appropriate information, interpret evidence and evaluate different theories about the Earth’s early atmosphere.

Recycling of gases - carbon cycle, global warming, oxygen balance and photosynthesis Revision Notes

Past ancient atmospheres, changes due to man's activities Revision Notes

Evolution of atmosphere - changes over billions of years, origin of life Revision Notes

9.1.3 How oxygen increased

Know that algae and plants produced the oxygen that is now in the atmosphere by photosynthesis, which can be represented by the equation:

water + carbon dioxide == sunlight energy ==> glucose sugar + oxygen 

6H₂O_(l) + 6CO_2(g) ==> C₆H₁₂O_6(aq) + 6O_2(g)

Algae first produced oxygen about 2.7 billion years ago and soon after this oxygen appeared in the atmosphere. Over the next billion years plants evolved and the percentage of oxygen gradually increased to a level that enabled animals to evolve.

Evolution of atmosphere - changes over billions of years, origin of life Revision Notes

9.1.4 How carbon dioxide decreased

Know that algae and plants decreased the percentage of carbon dioxide in the atmosphere by photosynthesis.

Carbon dioxide was also decreased by the formation of sedimentary rocks and fossil fuels that contain carbon.

Limestone is a sedimentary rock, mainly calcium carbonate, formed from the shells and skeletons of marine organisms.

Coal is a sedimentary rock formed from thick plant deposits that were buried and compressed over millions of years.

The remains of plankton were deposited in muds on the sea floor and were covered over and compressed over millions of years, producing crude oil and natural gas that became trapped in the rocks.

You should be able to :

describe the main changes in the atmosphere over time and some of the likely causes of these changes,

and describe and explain the formation of deposits of limestone, coal, crude oil and natural gas.
 

Evolution of atmosphere - changes over billions of years, origin of life Revision Notes

Word-fill quiz "The Evolution of the Earth's Atmosphere"

Word-fill quiz "More on the formation of the Earth's atmosphere"

Word-fill quiz "Later developments of the Earth's atmosphere"

Index of topics for AQA Combined Science Trilogy Chemistry paper 1 and paper 2

9.2 Carbon dioxide and methane as greenhouse gases

Greenhouse effect, global warming, climate change, carbon footprint from fossil fuel burning Revision Notes

9.2.1 Greenhouse gases

Know that greenhouse gases in the atmosphere maintain temperatures on Earth high enough to support life. They allow short wavelength radiation to pass through the atmosphere to the Earth’s surface but absorb the outgoing long wavelength radiation from the Earth causing an increase in temperature. Water vapour, carbon dioxide and methane are greenhouse gases.

You should be able to describe the greenhouse effect in terms of the interaction of short and long wavelength radiation with matter.

Greenhouse effect, global warming, climate change, carbon footprint from fossil fuel burning Revision Notes

9.2.2 Human activities which contribute to an increase in greenhouse gases in the atmosphere

(revision notes summary for AQA 9-1 GCSE Combined Science Trilogy: Chemistry Paper 4, Topic 16 "Chemistry of the atmosphere")

Know that some human activities increase the amounts of greenhouse gases in the atmosphere. These include carbon dioxide from combustion of fossil fuels, deforestation, methane from animal farming (digestion, waste decomposition) and decomposition of rubbish in landfill sites.

Appreciate that based on peer-reviewed evidence, many scientists believe that human activities will cause the temperature of the Earth’s atmosphere to increase at the surface and that this will result in global climate change. However, it is difficult to model such complex systems as global climate change. This leads to simplified models, speculation and opinions presented in the media that may be based on only parts of the evidence and which may be biased.

You should be able to:

evaluate the quality of evidence in a report about global climate change given appropriate information

describe uncertainties in the evidence base

recognise the importance of peer review of results and of communicating results to a wide range of audiences.

Greenhouse effect, global warming, climate change, carbon footprint from fossil fuel burning

Recycling of gases - carbon cycle, global warming, oxygen balance and photosynthesis Revision Notes

Past ancient atmospheres, changes due to man's activities Revision Notes
 

9.2.3 Global climate change

Know that an increase in average global temperature is a major cause of climate change. The potential effects of global climate change include eg sea level rise, which may cause flooding and increased coastal erosion, more frequent and severe storms, changes in the amount, timing and distribution of rainfall, temperature and water stress for humans and wildlife, changes in the food producing capacity of some regions and changes to the distribution of wildlife species.

You  should be able to:

describe briefly four potential effects of global climate change

discuss the scale, risk and environmental implications of global climate change.

Greenhouse effect, global warming, climate change, carbon footprint from fossil fuel burning Revision Notes

9.2.4 The carbon footprint and its reduction

Know that the carbon footprint is the total amount of carbon dioxide and other greenhouse gases emitted over the full life cycle of a product, service or event. The carbon footprint can be reduced by reducing emissions of carbon dioxide and methane.

Possible actions to reduce the carbon footprint include eg increased use of alternative energy supplies, energy conservation, carbon capture and storage, carbon taxes and licences, carbon off-setting, including through tree planting, carbon neutrality – zero net release.

Appreciate that problems of reducing the carbon footprint include eg scientific disagreement over causes and consequences of global climate change, lack of public information and education, lifestyle changes, economic considerations, incomplete international cooperation.

You should be able to:

describe how emissions of carbon dioxide and methane can be reduced

give reasons why actions may be limited.

Greenhouse effect, global warming, climate change, carbon footprint from fossil fuel burning

Word-fill quiz "Air pollution and the Earth's atmosphere"

Word-fill quiz "Making sense of air pollution data"

Index of topics for AQA Combined Science Trilogy Chemistry paper 1 and paper 2

9.3 Common atmospheric pollutants and their sources

9.3.1 Atmospheric pollutants from fuels 

(revision notes summary for AQA 9-1 GCSE Combined Science Trilogy: Chemistry Paper 4, Topic 16 "Chemistry of the atmosphere")

Know the combustion of fuels is a major source of atmospheric pollutants.

Most fuels, including coal, contain carbon and/or hydrogen and may also contain some sulfur.

The gases released into the atmosphere when a fuel is burned may include carbon dioxide, water vapour, carbon monoxide, sulfur dioxide and oxides of nitrogen. Solid particles and unburned hydrocarbons may also be released that form particulates in the atmosphere. Carbon monoxide and soot (carbon particles) are produced by incomplete combustion. Sulfur dioxide is produced by oxidation of sulfur in the fuel. Oxides of nitrogen are produced by the reaction of nitrogen and oxygen from the air at the high temperatures involved when fuels are burned.

You should be able to:

describe how carbon monoxide, soot (carbon particles), sulfur dioxide and oxides of nitrogen are produced by burning fuels

predict the products of combustion of a fuel given appropriate information about the composition of the fuel and the conditions in which it is used.

Air pollution - sulfur oxides, nitrogen oxides, acid rain Revision Notes

Air pollution - incomplete combustion, carbon monoxide & soot Revision Notes

9.3.2 Properties and effects of atmospheric pollutants

Know that carbon monoxide is a toxic gas. It is colourless and odourless and so is not easily detected. Carbon monoxide combines with haemoglobin in the blood, reducing its capacity to carry oxygen.

Sulfur dioxide and oxides of nitrogen cause respiratory problems in humans and cause acid rain.

Acid rain damages plants and buildings.

Particulates cause:

(i)  global dimming, reducing the amount of sunlight that reaches the Earth’s surface

(ii)  health problems for humans because of damage to the lungs.

You should be able to describe and explain the problems caused by increased amounts of pollutants in the air.

Air pollution - sulfur oxides, nitrogen oxides, acid rain Revision Notes

Air pollution - incomplete combustion, carbon monoxide & soot Revision Notes

Index of topics for AQA Combined Science Trilogy Chemistry paper 1 and paper 2

Topic 17 Using Resources  

(revision notes summary for AQA 9-1 GCSE Combined Science Trilogy: Chemistry Paper 4, Topic 17 "Using resources")

You should appreciate that industries use the Earth’s natural resources to manufacture useful products. In order to operate sustainably, chemists seek to minimise the use of limited resources, use of energy, waste and environmental impact in the manufacture of these products. Chemists also aim to develop ways of disposing of products at the end of their useful life in ways that ensure that materials and stored energy are utilised. Pollution, disposal of waste products and changing land use has a significant effect on the environment, and environmental chemists study how human activity has affected the Earth’s natural cycles, and how damaging effects can be minimised.

Using the Earth's resources INDEX - metals, oil, water etc. Revision Notes

HT = higher tier (harder - usually more theory & depth) and FT = foundation tier (easier)

10.1 Using the Earth's resources and obtaining potable water

(revision notes summary for AQA 9-1 GCSE Combined Science Trilogy: Chemistry Paper 4, Topic 17 "Using resources")

10.1.1 Using the Earth's resources and sustainable development

Appreciate that we humans use the Earth’s resources to provide warmth, shelter, food and transport.

Natural resources, supplemented by agriculture, provide food, timber, clothing and fuels.

Finite resources from the Earth, oceans and atmosphere are processed to provide energy and materials.

Chemistry plays an important role in improving agricultural and industrial processes to provide new products and in sustainable development, which is development that meets the needs of current generations without compromising the ability of future generations to meet their own needs.

You should be able to:

state examples of natural products that are supplemented or replaced by agricultural and synthetic products

distinguish between finite and renewable resources given appropriate information.

extract and interpret information about resources from charts, graphs and tables

use orders of magnitude to evaluate the significance of data.

An introduction to the Earth's resources & sustainability Revision Notes

Products of the Chemical & Pharmaceutical Industries & Impact on Us Revision Notes

Survey of the properties - related to uses, for a wide variety of materials Revision Notes

10.1.2 Potable water

Appreciate that water of appropriate quality is essential for life. For humans, drinking water should have sufficiently low levels of dissolved salts and microbes. Water that is safe to drink is called potable water. Potable water is not pure water in the chemical sense because it contains dissolved substances. The methods used to produce potable water depend on available supplies of water and local conditions.

In the United Kingdom (UK), rain provides water with low levels of dissolved substances (fresh water) that collects in the ground and in lakes and rivers, and most potable water is produced by:

choosing an appropriate source of fresh water

passing the water through filter beds

sterilising.

Sterilising agents used for potable water include chlorine, ozone or ultraviolet light. If supplies of fresh water are limited, desalination of salty water or sea water may be required. Desalination can be done by distillation or by processes that use membranes such as reverse osmosis. These processes require large amounts of energy.

You should be able to:

distinguish between potable water and pure water

describe the differences in treatment of ground water and salty water

give reasons for the steps used to produce potable water.

In required practical 8 you should have experienced analysis and purification of water samples from different sources, including pH, dissolved solids and distillation.

Water cycle, potable water, water treatment, pollution, tests for ions in water Revision Notes

Summary of tests for ions including equations Revision Notes

10.1.3 Waste water treatment

Appreciate that urban lifestyles and industrial processes produce large amounts of waste water that require treatment before being released into the environment. Sewage and agricultural waste water require removal of organic matter and harmful microbes. Industrial waste water may require removal of organic matter and harmful chemicals.

Sewage treatment includes:

screening and grit removal,

sedimentation to produce sewage sludge and effluent,

anaerobic digestion of sewage sludge,

aerobic biological treatment of effluent.

You should be able to comment on the relative ease of obtaining potable water from waste, ground and salt water.

Water cycle, potable water, water treatment, pollution, tests for ions in water Revision Notes

10.1.4 Alternative methods of extracting metals (HT only)

Appreciate that the Earth’s resources of metal ores are limited.

Copper ores are becoming scarce and new ways of extracting copper from low-grade ores include phytomining, and bioleaching. These methods avoid traditional mining methods of digging, moving and disposing of large amounts of rock.

Phytomining uses plants to absorb metal compounds. The plants are harvested and then burned to produce ash that contains the metal compounds.

Bioleaching uses bacteria to produce leachate solutions that contain metal compounds.

The metal compounds can be processed to obtain the metal. For example, copper can be obtained from solutions of copper compounds by displacement using scrap iron or by electrolysis.

You should be able to evaluate alternative biological methods of metal extraction, given appropriate information.

Copper extraction by phytomining or bioleaching Revision Notes

Index of topics for AQA Combined Science Trilogy Chemistry paper 1 and paper 2

10.2 Life cycle assessment and recycling

(revision notes summary for AQA 9-1 GCSE Combined Science Trilogy: Chemistry Paper 4, Topic 17 "Using resources")

10.2.1 Life cycle assessment

 Know that life cycle assessments (LCAs) are carried out to assess the environmental impact of products in each of these stages:

extracting and processing raw materials

manufacturing and packaging

use and operation during its lifetime

disposal at the end of its useful life, including transport and distribution at each stage.

Energy, water, resource consumption and production of some wastes can be fairly easily quantified. Allocating numerical values to pollutant effects is less straightforward and requires value judgements, so LCA is not a purely objective process.

Selective or abbreviated LCAs can be devised to evaluate a product but these can be misused to reach pre-determined conclusions, eg in support of claims for advertising purposes.

You should be able to carry out simple comparative LCAs for shopping bags made from plastic and paper.

LCAs should be done as a comparison of the impact on the environment of the stages in the life of a product, and only quantified where data is readily available for energy, water, resources and wastes.

Be able to interpret LCAs of materials or products given appropriate information.

Be able to recognise and use expressions in decimal form.

Be able to use ratios, fractions and percentages, make estimates of the results of simple calculations, use an appropriate number of significant figures and translate information between graphical and numeric form.

Chemical & Pharmaceutical Industry Economics & Sustainability, Life Cycle Assessment, Recycling Notes

10.2.2 Ways of reducing the use of resources

Know that the reduction in use, reuse and recycling of materials by end users reduces the use of limited resources, use of energy sources, waste and environmental impacts.

Metals, glass, building materials, clay ceramics and most plastics are produced from limited raw materials. Much of the energy for the processes comes from limited resources. Obtaining raw materials from the Earth by quarrying and mining causes environmental impacts.

Some products, such as glass bottles, can be reused. Glass bottles can be crushed and melted to make different glass products. Other products cannot be reused and so are recycled for a different use.

Metals can be recycled by melting and recasting or reforming into different products. The amount of separation required for recycling depends on the material and the properties required of the final product. For example, some scrap steel can be added to iron from a blast furnace to reduce the amount of iron that needs to be extracted from iron ore.

You should be able to evaluate ways of reducing the use of limited resources, given appropriate information.

Chemical & Pharmaceutical Industry Economics & Sustainability, Life Cycle Assessment, Recycling Notes

Economic & environmental issues on mineral extraction & reasons for recycling and methods Revision Notes

Index of topics for AQA Combined Science Trilogy Chemistry paper 1 and paper 2