OCR GCSE SCIENCES B (21st Century Science)

ALL MY GCSE CHEMISTRY REVISION NOTES

Revision summary help OCR GCSE 21st Century Combined Science B chemistry exam papers - learning objectives C4-6

OCR Level 1/2 GCSE (Grade 9-1) in Combined Science B Chemistry (Twenty First Century Science) (J260) - OCR 21st Century GCSE Grade 9-1 Combined Science B chemistry Chapter Chapter C4 "Material choices", Chapter C5 "Chemical analysis", Chapter C6 "Making useful chemicals", Chapter BCP7 "Ideas about science" for chemistry Paper 02/Paper 06

LINK for OCR 21st Century Combined Science chemistry chapters C1-C3

LINK for OCR 21st Century 9-1 GCSE CHEMISTRY B chapters C1-C3

LINK for OCR 21st Century 9-1 GCSE CHEMISTRY B chapters C4-C6

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

INDEX for all links * PAST PAPERS

PLEASE READ CAREFULLY THE FOLLOWING POINTS before using my OCR GCSE 21st Century science B pages

  1. ALL my unofficial GCSE (Grade 9-1) revision help summaries are based on the NEW 2016 official OCR 21st Century Science B (Grade 9-1) GCSE CHEMISTRY/combined science chemistry specifications.

  2. Make sure you know whether you are doing separate science OCR 21st Century Science B GCSE grade 9-1 CHEMISTRY OR OCR GCSE 21st Century Science B Combined Science chemistry.

  3. Also, make sure you know whether you are entered for a higher tier (HT) or a foundation tier (FT) OCR GCSE 21st Century 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 OCR GCSE 21st Century 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. OCR GCSE 21st Century Combined Science 2nd chemistry paper, PAST PAPERS, specimen practice paper questions

  7. '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!

  8. 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.

In OCR 9-1 GCSE Twenty First Century Combined Science B chemistry courses, note the following!

Note: Combined Science Paper 04/Paper 08 assesses the contents of ALL the chapters of biology, chemistry and physics!



Syllabus-specification CONTENT INDEX of revision summary notes

What's assessed in this paper?    (OCR 9-1 GCSE Twenty First Century Combined Science Chemistry)

SUMMARY Chapter C1: Air and water    (separate page)

Chapter C1.1 How has the Earth’s atmosphere changed over time, and why?

Chapter C1.2 Why are there temperatures changes in chemical reactions?

Chapter C1.3 What is the evidence for climate change, why is it occurring?

Chapter C1.4 How can scientists help improve the supply of potable water?

SUMMARY Chapter C2: Chemical patterns    (separate page)

Chapter C2.1 How have our ideas about atoms developed over time?

Chapter C2.2 What does the Periodic Table tell us about the elements?

Chapter C2.3 How do metals and non-metals combine to form compounds?

Chapter C2.4 How are equations used to represent chemical reactions?

SUMMARY Chapter C3: Chemicals of the natural environment    (separate page)

Chapter C3.1 How are the atoms held together in a metal?

Chapter C3.2 How are metals with different reactivities extracted?

Chapter C3.3 What are electrolytes and what happens during electrolysis?

Chapter C3.4 Why is crude oil important as a source of new materials?

SUMMARY Chapter C4: Material choices   (this page)

Revision summary Chapter C4.1 How is data used to choose a material for a particular use?

Revision summary Chapter C4.2 How do bonding and structure affect properties of materials?

Revision summary Chapter C4.3 Why are nanoparticles so useful?

Revision summary Chapter C4.4 What happens to products at the end of their useful life?

SUMMARY Chapter C5: Chemical analysis  (this page)

Revision summary Chapter C5.1 How are chemicals separated and tested for purity?

Revision summary Chapter C5.2 How are the amounts of substances in reactions calculated?

Revision summary Chapter C5.3 How are the amounts of chemicals in solution measured?

SUMMARY Chapter C6: Making useful chemicals  (this page)

Revision summary Chapter C6.1 What useful products can be made from acids?

Revision summary Chapter C6.2 How do chemists control the rate of reactions?

Revision summary Chapter C6.3 What factors affect the yield of chemical reactions?

SUMMARY Chapter BCP7: Ideas about Science  (this page)

IaS1 What needs to be considered when investigating a phenomenon scientifically?

IaS2 What conclusions can we make from data?

IaS3 How are scientific explanations developed?

IaS4 How do science and technology impact society?

Note: Combined Science Paper 04/Paper 08 assesses the contents of ALL the chapters of biology, chemistry and physics!


Chapter C4: Material choices  

 (Revision for OCR GCSE 9–1 Twenty First Century Science Combined Science B chemistry 02, Topics for Chapter C4 "Material choices")


Overview of Chapter C4 Material choices  (OCR 9-1 GCSE 21st Century Combined Science B Chemistry)

Our society uses a large range of materials and products that have been developed, tested and modified by the work of chemists. Materials used to make a particular product need to meet a specification which describes the properties the material needs to make it suitable for a particular use. This chapter looks at a range of different materials and investigates their properties in the context of their suitability for making consumer products. The chapter also considers how the life cycle of a product is assessed in its journey from raw material to final disposal.

Topic C4.1 considers the variety of materials that we use. You use data and information about the properties of ‘pure’ and composite materials to consider their suitability for making consumer products. Ceramics, glass, polymers, materials with giant structure and polymers are all considered.

Topic C4.2 extends the study of properties to looking at bonding and structure in order to explain why a particular material behaves as it does. You learn about the bonding in metals, polymers and giant covalent structures and link the bonding and structure to the properties of the materials. They consider the usefulness of diagrams and models of bonding and structure to chemists who need to investigate and predict properties of materials so that they can make judgements about their usefulness or model likely changes in their properties if their structures are modified. A range of materials are studied, including new materials such as fullerenes and graphene.

Topic C4.3 looks specifically at the nature and uses of nanoparticles.

Topic C4.4 considers the life cycle of materials. You learn how the impact of our manufacture, use and disposal of consumer products is assessed using life cycle assessments.



Chapter C4 Material choices

 (Revision for OCR GCSE 9–1 Twenty First Century Science Combined Science B chemistry 02, Topics for Chapter C4 "Material choices")

Quiz on selected aspects of OCR Twenty First Century GCSE 9-1 Combined Science Chapter C4 "Material choices"

The quiz consists of mainly structure and bonding questions - structure and properties of ionic, covalent, giant covalent and metallic materials. (Higher Tier/Foundation Tier)

for HT students Chapter C4 "Material choices" QUIZ (OCR 21st GCSE 9-1 Chemistry-Combined Science B)

for FT students Chapter C4 "Material choices" QUIZ (OCR 21st GCSE 9-1 Chemistry-Combined Science B)

HT = higher tier (harder - usually more theory & depth), FT = foundation tier (easier) 1st drafts 21st Century chemistry quizzes


What you learned about material choices before 21st Century GCSE (9–1) Science Chemistry

From study at Key Stages 1 to 3 you should:

• distinguish between an object and the material from which it is made

• identify and name a variety of everyday materials, including wood, plastic, glass, metal, water, and rock

• describe the simple physical properties of a variety of everyday materials

• compare and group together a variety of everyday materials on the basis of their simple physical properties.

• have observed that some materials change state when they are heated or cooled, and measured the temperature at which this happens in degrees Celsius (°C)

• compare and group together everyday materials on the basis of their properties, including their hardness, solubility, transparency, conductivity (electrical and thermal), and response to magnets

• identify and compare the suitability of a variety of everyday materials, including wood, metal, plastic, glass, brick, rock, paper and cardboard for particular use

• know the differences between atoms, elements and compounds

• recognise chemical symbols and formulae for some elements and compounds

• know about the properties of ceramics, polymers and composites (qualitative)


Chapter C4.1 How is data used to choose a material for a particular use?

 (Revision for OCR GCSE 9–1 Twenty First Century Science Combined Science B chemistry 02, Topics for Chapter C4 "Material choices")

Our society uses a large range of materials and products developed by chemists. Chemists assess materials by measuring their physical properties, and use data to compare different materials and to match materials to the specification of a useful product.

Composites have a very broad range of uses as they allow the properties of several materials to be combined. Composites may have materials combined on a bulk scale (for example using steel to reinforce concrete) or have nanoparticles incorporated in a material or embedded in a matrix.

1. Be able to compare quantitatively the physical properties of glass and clay ceramics, polymers, composites and metals, including melting point, softening temperature (for polymers), electrical conductivity, strength (in tension or compression), stiffness, flexibility, brittleness, hardness, density, ease of reshaping.

Practical work: Investigating of a range of materials leading to classification into categories.

2. Be able to explain how the properties of materials are related to their uses and select appropriate materials given details of the usage required.

The range of materials developed by chemists enhances the quality of life.

Use and limitations of a model to represent alloy structure.

Help links for C4.1

Addition polymers, plastics, uses and problems

Comparing addition polymers and condensation polymers, thermosets, fibres, thermosoftening etc.

Metals – structure and properties (including alloys)

Transition Metals eg uses of iron and copper plus mention of aluminium

Notes on concrete, glass, clay ceramics, bricks etc.

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


C4.2 How do bonding and structure affect properties of materials?

 (Revision for OCR GCSE 9–1 Twenty First Century Science Combined Science B chemistry 02, Topics for Chapter C4 "Material choices")

Different materials can be made from the same atoms but have different properties if they have different types of bonding or structures. Chemists use ideas about bonding and structure when they predict the properties of a new material or when they are researching how an existing material can be adapted to enhance its properties.

Carbon is an unusual element because it can form chains and rings with itself. This leads to a vast array of natural and synthetic compounds of carbon with a very wide range of properties and uses. ‘Families’ of carbon compounds are homologous series.

1. Be able to explain how the bulk properties of materials (including strength, melting point, electrical and thermal conductivity, brittleness, flexibility, hardness and ease of reshaping) are related to the different types of bonds they contain, their bond strengths in relation to intermolecular forces and the ways in which their bonds are arranged, recognising that the atoms themselves do not have these properties.

Links ionic bonding and structure (C2.3) metallic bonding (C3.1) covalent bonds and intermolecular forces (C3.4)

Practical work: Testing the properties of simple covalent compounds, giant ionic and giant covalent substances, metals and polymers.

Ionic bonding and ionic compounds and their properties

Covalent bonding and small molecules and their properties

Covalent bonding and giant structures and their properties and uses

Metallic bonding, properties and uses of metals

Addition polymer structure - properties and uses

Comparing addition and condensation polymer structure - properties and uses

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

Quiz on the Structure, Properties and Chemical Bonding of Materials

Introduction to Chemical Bonding (includes an exercise near the end of the page to deduce structure of a material from given information, best done after all relevant sections studied!)

2. Be able to recall that carbon can form four covalent bonds

The alkanes as a homologous series.

Identify patterns in data related to polymers and allotropes of carbon

Alkanes - saturated hydrocarbons, structure and names

Addition polymer structure - properties and uses

Covalent bonding and giant structures and their properties and uses

3. Be able to explain that the vast array of natural and synthetic organic compounds occurs due to the ability of carbon to form families of similar compounds, chains and rings.

Introduction to Organic Chemistry - Why so many series of organic compounds?

Polymer molecules have the same strong covalent bonding as simple molecular compounds, but there are more intermolecular forces between the molecules due to their length. The strength of the intermolecular forces affects the properties of the solid.

Giant covalent structures contain many atoms bonded together in a three-dimensional arrangement by covalent bonds. The ability of carbon to bond with itself gives rise to a variety of materials which have different giant covalent structures of carbon atoms. These are allotropes, and include diamond and graphite. These materials have different properties which arise from their different structures.

Covalent bonding and giant structures and their properties and uses

4. Be able to describe the nature and arrangement of chemical bonds in polymers with reference to their properties including strength, flexibility or stiffness, hardness and melting point of the solid.

Addition polymer structure - properties and uses

Comparing addition and condensation polymer structure - properties and uses

5. Be able to describe the nature and arrangement of chemical bonds in giant covalent structures.

6. Be able to explain the properties of diamond and graphite in terms of their structures and bonding, include melting point, hardness and (for graphite) conductivity and lubricating action.

Covalent bonding and giant structures and their properties and uses

7. Be able to represent three dimensional shapes in two dimensions and vice versa when looking at chemical structures e.g. allotropes of carbon.

Covalent bonding and giant structures and their properties and uses

8. Be able to describe and compare the nature and arrangement of chemical bonds in ionic compounds, simple molecules, giant covalent structures, polymers and metals.

Ionic bonding and ionic compounds and their properties

Covalent bonding and small molecules and their properties

Covalent bonding and giant structures and their properties and uses

Metallic bonding, properties and uses of metals

Addition polymer structure - properties and uses

Comparing addition and condensation polymer structure - properties and uses

Survey of properties related to uses of a wide variety of materials - metals, polymers, composites, ceramics

Quiz on the Structure, Properties and Chemical Bonding of Materials


Chapter C4.3 Why are nanoparticles so useful?

 (Revision for OCR GCSE 9–1 Twenty First Century Science Combined Science B chemistry 02, Topics for Chapter C4 "Material choices")

Nanoparticles have a similar scale to individual molecules. Their extremely small size means they can penetrate into biological tissues and can be incorporated into other materials to modify their properties. Nanoparticles have a very high surface area to volume ratio. This makes them excellent catalysts.

Fullerenes form nanotubes and balls. The ball structure enables them to carry small molecules, for example carrying drugs into the body. The small size of fullerene nanotubes enables them to be used as molecular sieves and to be incorporated into other materials (for example to increase strength of sports equipment). Graphene sheets have specialised uses because they are only a single atom thick but are very strong with high electrical and thermal conductivity.

Developing technologies based on fullerenes and graphene required leaps of imagination from creative thinkers.

There are concerns about the safety of some nanoparticles because not much is known about their effects on the human body. Judgements about a particular use for nanoparticles depend on balancing the perceived benefit and risk.

1. Be able to compare ‘nano’ dimensions to typical dimensions of atoms and molecules.

2. Be able to describe the surface area to volume relationship for different-sized particles and describe how this affects properties.

3. Be able to describe how the properties of nanoparticulate materials are related to their uses including properties which arise from their size, surface area and arrangement of atoms in tubes or rings.

Discussion of the potential benefits and risks of developments in nanotechnology.

Development of nanoparticles and graphene relied on imaginative thinking.

General introduction to nanoscience and commonly used terms explained

Nanochemistry - an introduction and potential applications

4. Be able to explain the properties fullerenes and graphene in terms of their structures.

Fullerenes; bucky balls and carbon nanotubes and Graphene

5. Be able to explain the possible risks associated with some nanoparticulate materials including:

(a) possible effects on health due to their size and surface area

(b) reasons that there is more data about uses of nanoparticles than about possible health effects

(c) the relative risks and benefits of using nanoparticles for different purposes.

Uses of Nanoparticles of titanium(IV) oxide, fat and silver

Problems, issues and implications associated with using nanomaterials

Appreciate a particular use for nanoparticles depends on balancing the perceived benefit and risk.

6. Be able to estimate size and scale of atoms and nanoparticles including the ideas that:

(a) nanotechnology is the use and control of structures that are very small (1 to 100 nanometres in size)

(b) data expressed in nanometres is used to compare the sizes of nanoparticles, atoms and molecules.

7. Be able to interpret, order and calculate with numbers written in standard form when dealing with nanoparticles.

8. Be able to use ratios when considering relative sizes and surface area to volume comparisons.

9. Be able to calculate surface areas and volumes of cubes.

General introduction to nanoscience and commonly used terms explained

Nanochemistry - an introduction and potential applications


Chapter C4.4 What happens to products at the end of their useful life?

 (Revision for OCR GCSE 9–1 Twenty First Century Science Combined Science B chemistry 02, Topics for Chapter C4 "Material choices")

Iron is the most widely used metal in the world. The useful life of products made from iron is limited because iron corrodes. This involves an oxidation reaction with oxygen from the air.

Life cycle assessments (LCAs) are used to consider the overall impact of our making, using and disposing of a product. LCAs involve considering the use of resources and the impact on the environment of all stages of making materials for a product from raw materials, making the finished product, the use of the product, transport and the method used for its disposal at the end of its useful life.

It is difficult to make secure judgments when writing LCAs because there is not always enough data and people do not always follow recommended disposal advice.

Some products can be recycled at the end of their useful life. In recycling, the products are broken down into the materials used to make them; these materials are then used to make something else. Reusing products uses less energy than recycling them. Reusing and recycling both affects the LCA.

Recycling conserves resources such as crude oil and metal ores, but will not be sufficient to meet future demand for these resources unless habits change.

The viability of a recycling process depends on a number of factors: the finite nature of some deposits of raw materials (such as metal ores and crude oil), availability of the material to be recycled, economic and practical considerations of collection and sorting, removal of impurities, energy use in transport and processing, scale of demand for new product, environmental impact of the process.

Products made from recycled materials do not always have a lower environmental impact than those made from new resources.

Practical work:

Investigating the factors needed for rusting of iron or corrosion of other metals.

Investigating the effectiveness of corrosion prevention (barrier and sacrificial protection methods).

Introduction to oxidation and reduction theory and application to 'redox' reactions

Applying scientific solutions to the problem of corrosion of metals to explain the idea of improving sustainability.

The corrosion of metals and the prevention of iron rusting

Electrolysis and electroplating

Be able to use life cycle assessments to compare the sustainability of products and processes.

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

1. Be able to explain reduction and oxidation in terms of loss or gain of oxygen, identifying which species are oxidised and which are reduced.

2. (HT only) Be able to explain reduction and oxidation in terms of gain or loss of electrons, identifying which species are oxidised and which are reduced.

Introduction to oxidation and reduction and their application to reactions

3. Be able to describe the basic principles in carrying out a life-cycle assessment of a material or product including:

(a) the use of water, energy and the environmental impact of each stage in a life cycle, including its manufacture, transport and disposal

(b) incineration, landfill and electricity generation schemes

(c) biodegradable and non-biodegradable materials

4. Be able to interpret data from a life-cycle assessment of a material or product.

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

5. Be able to describe the process where PET drinks bottles are reused and recycled for different uses, and explain why this is viable.

6. Be able to evaluate factors that affect decisions on recycling with reference to products made from crude oil and metal ores.

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

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


Chapter C5:  Chemical analysis  

 (Revision for OCR GCSE 9–1 Twenty First Century Science Combined Science B chemistry 02, Topics for Chapter C5 "Chemical analysis")


This chapter looks at how chemicals are analysed. Chemical analysis is important in chemistry for the quality control of manufactured products and also to identify or quantify components in testing of new products, mineral extraction, forensics and environmental monitoring. Chemists need to both identify which substances are present (qualitative analysis) and the quantity of each substance (quantitative analysis). Measuring purity and separating mixtures is important in manufacturing to ensure quality and to separate useful products from bi-products and waste. Being able to analyse quantities of chemicals enables chemists to plan for the amounts of reactants they need to use to make a product, or predict quantities of products from known amounts of reactants.

The chapter begins in Topic C5.1 by considering why it is necessary to purify chemicals and how the components of mixtures are separated. Methods of testing for purity and separating mixtures are studied, including chromatography and a range of practical separation techniques.

Topic C5.2 introduces quantitative work. The mole is used as a measure of amounts of substance and learners process data from formulae and equations to work out quantities of reactants and products.

Topic C5.3 develops quantitative work further to show how the concentrations of solutions are determined. This has applications for the testing and quality control of manufactured chemical products and also allows the analysis of unknown chemicals for a range of purposes (for example in forensics, in drug production, mineral exploration and environmental monitoring). You learn how to make a standard solution and analyse the concentration of unknown solutions using titrations.



Chapter C5 Chemical analysis

 (Revision for OCR GCSE 9–1 Twenty First Century Science Combined Science B chemistry 02, Topics for Chapter C5 "Chemical analysis")

Quiz on selected aspects of OCR Twenty First Century GCSE 9-1 Combined Science B Chapter C5 "Chemical analysis": simple chemical calculations, more advanced calculations - molarity, quantitative analysis, qualitative analysis for ions - cations and anions, (Higher Tier/Foundation Tier)

for HT students Chapter C5 "Chemical analysis" QUIZ (OCR 21st GCSE 9-1 Combined Science B)

for FT students Chapter C5 "Chemical analysis" QUIZ (OCR 21st GCSE 9-1 Combined Science B)

HT = higher tier (harder - usually more theory & depth), FT = foundation tier (easier) 1st drafts 21st Century chemistry quizzes


What you learned about chemical analysis before OCR GCSE (9–1) 21st Century Combined Science B Chemistry

From study at Key Stages 1 to 3 you should:

• use knowledge of solids, liquids and gases to decide how mixtures might be separated, including through filtering, sieving and evaporating

• understand the concept of a pure substance and how to identify a pure substance

• know about simple techniques for separating mixtures: filtration, evaporation, distillation and chromatography

• know about the pH scale for measuring acidity/ alkalinity; and indicators.


Chapter C5.1 How are chemicals separated and tested for purity?

 (Revision for OCR GCSE 9–1 Twenty First Century Science Combined Science B chemistry 02, Topics for Chapter C5 "Chemical analysis")

Many useful products contain mixtures. It is important that consumer products such as drugs or personal care products do not include impurities. Mixtures in many consumer products contain pure substances mixed together in definite proportions called formulations. Pure substances contain a single element or compound. Chemists test substances made in the laboratory and in manufacturing processes to check that they are pure. One way of assessing the purity of a substance is by testing its melting point; pure substances have sharp melting points and can be identified by matching melting point data to reference values.

Chromatography is used to see if a substance is pure or to identify the substances in a mixture. Components of a mixture are identified by the relative distance travelled compared to the distance travelled by the solvent. Rf values can be calculated and used to identify unknown components by comparison to reference samples. Some substances are insoluble in water, so other solvents are used. Chromatography can be used on colourless substances but locating agents are needed to show the spots.

Preparation of chemicals often produces impure products or a mixture of products. Separation processes in both the laboratory and in industry enable useful products to be separated from bi-products and waste products. The components of mixtures are separated using processes that exploit the different properties of the components, for example state, boiling points or solubility in different solvents.

Separation processes are rarely completely successful and mixtures often need to go through several stages or through repeated processes to reach an acceptable purity.

1. Be able to explain that many useful materials are formulations of mixtures.

Links: Particle model and changes of state (C1.1)

Fractional distillation of crude oil on an industrial scale (C3.4)

Using the particle model to explain the idea of a pure substance

Introduction to formulation mixtures

2. Be able to explain what is meant by the purity of a substance, distinguishing between the scientific and everyday use of the term ‘pure’.

3. Be able to use melting point data to distinguish pure from impure substances.

Definitions  and criteria in Chemistry eg element, compound, mixture, pure, impure and test criteria

4. Be able to recall that chromatography involves a stationary and a mobile phase and that separation depends on the distribution between the phases.

5. Be able to interpret chromatograms, including calculating Rf values.

6. Be able to suggest chromatographic methods for distinguishing pure from impure substances.

Including the use of: (a) paper chromatography, (b) aqueous and non-aqueous solvents, (c) locating agents

Paper chromatography

7. Be able to describe, explain and exemplify the processes of filtration, crystallisation, simple distillation, and fractional distillation.

Distillation - Simple and Fractional Distillation 

Filtration, evaporation, crystallisation, drying and decantation

8. Be able to suggest suitable purification techniques given information about the substances involved

Methods of Separating Mixtures of substances


Chapter C5.2 How are the amounts of substances in reactions calculated?

 (Revision for OCR GCSE 9–1 Twenty First Century Science Combined Science B chemistry 02, Topics for Chapter C5 "Chemical analysis")

During reactions, atoms are rearranged but the total mass does not change. Reactions in open systems often appear to have a change in mass because substances are gained or lost, usually to the air. Chemists use relative masses to measure the amounts of chemicals. Relative atomic masses for atoms of elements can be obtained from the Periodic Table. The relative formula mass of a compound can be calculated using its formula and the relative atomic masses of the atoms it contains.

(HT only) Relative masses are based on the mass of carbon 12. Counting atoms or formula units of compounds involves very large numbers, so chemists use a mole as a unit of counting. One mole contains the same number of particles as there are atoms in 12g of carbon -12, and has the value 6.0 x 1023 atoms; this is the Avogadro constant. It is more convenient to count atoms as ‘numbers of moles’.

(HT only) The number of moles of a substance can be worked out from its mass, this is useful to chemists because they can use the equations for reactions to work out the amounts of reactants to use in the correct proportions to make a particular product, or to work out which reactant is used up when a reaction stops.

1. Be able to recall and use the law of conservation of mass.

The particle model (C1.1) Maximising industrial yields (C6.3)

Practical Work: Comparison of theoretical and actual yield from the preparation of an organic compound (introduced in C3) or a salt (introduced in C5).

Testing predictions of volumes of gases produced from reactions of acids.

Making and testing predictions. Carrying out investigations. Analysing and evaluating data.

Investigations. Using measuring apparatus. Safe handling of chemicals.

Using data to make quantitative predictions about yields and comparing them to actual yields.

Law of Conservation of Mass and simple reacting mass calculations

Type in answer quiz on the law of conservation of mass

Multiple choice quiz on the law of conservation of mass

% reaction yield definition and theoretical yield calculations, why never 100%

Moles and the molar volume of a gas, Avogadro's Law

Molar gas volume type in answer QUIZ

Molar gas volume multiple choice QUIZ

2. Be able to explain any observed changes in mass in non-enclosed systems during a chemical reaction and explain them using the particle model.

Law of Conservation of Mass and simple reacting mass calculations

Type in answer quiz on the law of conservation of mass

Multiple choice quiz on the law of conservation of mass

3. Be able to calculate relative formula masses of species separately and in a balanced chemical equation.

Calculating relative formula/molecular mass (Mr) of a compound or element molecule

Type in answer quiz on relative formula mass

Multiple Choice quiz on relative formula mass

4. (HT only) Be able to recall and use the definitions of the Avogadro constant (in standard form) and of the mole.

5. (HT only) Be able to explain how the mass of a given substance is related to the amount of that substance in moles and vice versa and use the relationship:

number of moles = mass of substance (g) / relative formula mass (g)

Introducing moles: The connection between moles, mass and formula mass - the basis of reacting mole ratio calculations (relating reacting masses and formula mass), Avogadro constant

6. (HT only) Be able to deduce the stoichiometry of an equation from the masses of reactants and products and explain the effect of a limiting quantity of a reactant.

Law of Conservation of Mass and simple reacting mass calculations

Type in answer quiz on the law of conservation of mass

Multiple choice quiz on the law of conservation of mass

Reacting mass ratio calculations of reactants and products from equations (NOT using moles)

Type in answer QUIZ on reacting masses

Multiple choice QUIZ on reacting masses

How much of a reactant is needed? calculation of quantities required, limiting quantities

Mole ratio calculations - equation interpretation and construction of balanced chemical equations

Introduction to moles type in answer QUIZ

Introduction to moles multiple choice QUIZ

7. Be able to use a balanced equation to calculate masses of reactants or products.

Reacting mass ratio calculations of reactants and products from equations (NOT using moles)

Mole ratio calculations - equation interpretation and construction of balanced chemical equations

 (HT only) The equation for a reaction can also be used to work out how much product can be made starting from a known amount of reactants. This is useful to determine the amounts of reacting chemicals to be used in industrial processes so that processes can run as efficiently as possible. Chemists use the equation for a reaction to calculate the theoretical, expected yield of a product. This can then be compared to the actual yield. Actual yields are usually much lower than theoretical yields. This can be caused by a range of factors including reversible reactions, impurities in reactants or reactants and products being lost during the procedure. Information about actual yields is used to make improvements to procedures to maximise yields.

8. Be able to use arithmetic computation, ratio, percentage and multistep calculations throughout quantitative chemistry.

9. (HT only) Be able to carry out calculations with numbers written in standard form when using the Avogadro constant.

Introducing moles - using the Avogadro constant

10. Be able to change the subject of a mathematical equation.


Chapter C5.3 How are the amounts of chemicals in solution measured?

 (Revision for OCR GCSE 9–1 Twenty First Century Science Combined Science B chemistry 02, Topics for Chapter C5 "Chemical analysis")

 (HT only) Quantitative analysis is used by chemists to make measurements and calculations to show the amounts of each component in a sample.

 (HT only) Concentrations sometimes use the units g/dm3 but more often are expressed using moles, with the units mol/dm3. Expressing concentration using moles is more useful because it links more easily to the reacting ratios in the equation.

The concentration of acids and alkalis can be analysed using titrations. Alkalis neutralise acids. An indicator is used to identify the point when neutralisation is just reached. During the reaction, hydrogen ions from the acid react with hydroxide ions from the alkali to form water. The reaction can be represented using the equation H+(aq) + OH-(aq) ==>  H2O(l)

As with all quantitative analysis techniques, titrations follow a standard procedure to ensure that the data is collected safely and is of high quality, including selecting samples, making rough and multiple repeat readings and using equipment of an appropriate precision (such as a burette and pipette).

Data from titrations can be assessed in terms of its accuracy, precision and validity. An initial rough measurement is used as an estimate and titrations are repeated until a level of confidence can be placed in the data; the readings must be close together with a narrow range. The true value of a titration measurement can be estimated by discarding roughs and taking a mean of the results which are in close agreement. The results of a titration and the equation for the reaction are used to work out the concentration of an unknown acid or alkali.

1. (HT only) Be able to explain how the mass of a solute and the volume of the solution is related to the concentration of the solution and calculate concentration using the formula:

concentration (g/dm3) = mass of solute (g) / volume (dm3)

Concentration of solution in terms of mass and volume

2. (HT only) Be able to explain how the concentration of a solution in mol/dm3 is related to the mass of the solute and the volume of the solution and calculate the molar concentration using the formula:

concentration (mol/dm3) = number of moles of solute / volume (dm3)

Practical work:

Acid-base titrations.

Use of appropriate measuring apparatus, measuring pH, use of a volumetric flask to make a standard solution, titrations using burettes and pipettes, use of acid-base indicators, safe handling of chemicals.

Links: Strong and weak acid chemistry (C6.1)

Introducing moles: The connection between moles, mass and formula mass

Introduction to moles type in answer QUIZ

Introduction to moles multiple choice QUIZ

Molarity, volumes and solution concentrations (and diagrams of apparatus)

Molarity type in answer QUIZ

Molarity multiple choice QUIZ

How to do titrations and calculations e.g. acid-alkali titrations (and diagrams of apparatus)

Titration type in answer QUIZ

Titration multiple choice QUIZ

3. Be able to describe neutralisation as acid reacting with alkali to form a salt plus water including the common laboratory acids hydrochloric acid, nitric acid and sulfuric acid and the common alkalis, the hydroxides of sodium, potassium and calcium.

Reactions of acids with hydroxides &carbonates - neutralisation reactions

4. Be able to recall that acids form hydrogen ions when they dissolve in water and solutions of alkalis contain hydroxide ions.

5. Be able to recognise that aqueous neutralisation reactions can be generalised to hydrogen ions reacting with hydroxide ions to form water.

pH scale, indicator colours, ionic theory of acids, alkalis (bases) & neutralisation

6. Be able to describe and explain the procedure for a titration to give precise, accurate, valid and repeatable results

Be able to justify a technique in terms of precision, accuracy and validity of data to be collected, minimising risk.

Be able to use of range and mean when processing titration results, analysis of data.

7. Be able to evaluate the quality of data from titrations


Chapter C6: Making useful chemicals

 (Revision for OCR GCSE 9–1 Twenty First Century Science Combined Science B chemistry 02, Topics for Chapter C6 "Making useful chemicals")


Overview of Chapter C6 Making useful chemicals

This unit considers the laboratory and large-scale production of useful chemicals.

Topic 6.1 begins with the laboratory synthesis of salts from acid reactions, and also looks at the characteristics of both acids and bases.

In Topic C6.2, the story moves on to study how chemists manage the rate of reaction when these reactions take place, in the context of managing conditions both in the laboratory and in industry. This chapter gives the opportunity for a wide range of practical investigation and mathematical analysis of rates.

Topic C6.3 looks at reversible reactions, with particular emphasis on the large scale production of ammonia.



C6 Making useful chemicals

 (Revision for OCR GCSE 9–1 Twenty First Century Science Combined Science B chemistry 02, Topics for Chapter C6 "Making useful chemicals")

Quiz on selected aspects of OCR Twenty First Century GCSE 9-1 Combined Science B Chapter C6 "Making useful chemicals": reactions of acids, making salts, rates of reaction - experiments and factors - concentration, temperature, pressure, enzymes, catalysts, manufacture of ammonia (Haber synthesis), ammonium salts  (Higher Tier/Foundation Tier)

for HT students Chapter C6 "Making useful chemicals" QUIZ (OCR 21st GCSE 9-1 Combined Science B)

for FT students Chapter C6 "Making useful chemicals" QUIZ (OCR 21st GCSE 9-1 Combined Science B)

HT = higher tier (harder - usually more theory & depth), FT = foundation tier (easier) 1st drafts 21st Century chemistry quizzes


What you should have learned about Making useful Chemicals before GCSE (9–1) OCR 21st Century Combined Science B chemistry

From study at Key Stages 1 to 3 you should:

• explain that some changes result in the formation of new materials, and that this kind of change is not usually reversible

• represent chemical reactions using formulae and using equations

• define acids and alkalis in terms of neutralisation reactions

• describe the pH scale for measuring acidity/ alkalinity; and indicators

• recall reactions of acids with metals to produce a salt plus hydrogen and reactions of acids with alkalis to produce a salt plus water

• know what catalysts do.

• know about energy changes on changes of state (qualitative)

• know about exothermic and endothermic chemical reactions (qualitative).


Chapter C6.1 What useful products can be made from acids?

 (Revision for OCR GCSE 9–1 Twenty First Century Science Combined Science B chemistry 02, Topics for Chapter C6 "Making useful chemicals")

Many products that we use every day are based on the chemistry of acid reactions. Products made using acids include cleaning products, pharmaceutical products and food additives. In addition, acids are made on an industrial scale to be used to make bulk chemicals such as fertilisers. Acids react in neutralisation reactions with metals, hydroxides and carbonates. All neutralisation reactions produce salts, which have a wide range of uses and can be made on an industrial scale.

(HT only) The strength of an acid depends on the degree of ionisation and hence the concentration of H+ ions, which determines the reactivity of the acid. The pH of a solution is a measure of the concentration of H+ ions in the solution. Strong acids ionise completely in solution, weak acids do not. Both strong and weak acids can be prepared at a range of different concentrations (i.e. different amounts of substance per unit volume).

(HT only) Weak acids and strong acids of the same concentration have different pH values. Weak acids are less reactive than strong acids of the same concentration (for example they react more slowly with metals and carbonates).

1. Be able to recall that acids react with some metals and with carbonates and write equations predicting products from given reactants.

Writing formulae, balanced symbol and ionic equations.(C3.2), Concentration of solutions (C5.4)

Practical Work: Reactions of acids and preparation of salts, pH testing

Investigating strong and weak acid reactivity

use of indicators to test strong and weak acids

making standard solutions using volumetric flasks.

Reactions of acids with metals and carbonates

2. Be able to describe practical procedures to make salts to include appropriate use of filtration, evaporation, crystallisation and drying.

Making a soluble salt by neutralising a soluble acid with a soluble base (alkali)

Making a soluble salt by from an acid with a metal or insoluble base – oxide, hydroxide or carbonate

Preparing an insoluble salt by mixing solutions of two soluble compounds

3. Be able to use the formulae of common ions to deduce the formula of a compound.

How to write word & balance symbol equations, work out formula and name compounds

Ionic compounds section on working out formulae

4. Be able to recall that relative acidity and alkalinity are measured by pH including the use of universal indicator and pH meters.

Everyday examples of acid-alkali chemistry - examples and uses of acids and alkalis (pH quoted too)

pH scale, indicator colours, ionic theory of acids, alkalis (bases) & neutralisation

5. (HT only) Be able to use and explain the terms dilute and concentrated (amount of substance) and weak and strong (degree of ionisation) in relation to acids including differences in reactivity with metals and carbonates.

More on Acid-Base Theory and Weak and Strong Acids

6. (HT only) Be able to use the idea that as hydrogen ion concentration increases by a factor of ten the pH value of a solution decreases by one

pH scale, indicator colours, ionic theory of acids, alkalis (bases) & neutralisation

7. (HT only) Be able to describe neutrality and relative acidity and alkalinity in terms of the effect of the concentration of hydrogen ions on the numerical value of pH (whole numbers only)

pH scale, indicator colours, ionic theory of acids

Multiple choice quiz on pH, Indicators, Acids, Bases, Neutralisation and Salts

Structured question worksheet on Acid Reaction word equations and symbol equation question

Word equation answers and symbol equation answers

Word-fill worksheet on Acids, Bases, Neutralisation and Salts

Matching pair quiz on Acids, Bases, Salts and pH


Chapter C6.2 How do chemists control the rate of reactions?

 (Revision for OCR GCSE 9–1 Twenty First Century Science Combined Science B chemistry 02, Topics for Chapter C6 "Making useful chemicals")

Controlling rate of reaction enables industrial chemists to optimise the rate at which a chemical product can be made safely.

The rate of a reaction can be altered by altering conditions such as temperature, concentration, pressure and surface area. A model of particles colliding helps to explain why and how each of these factors affects rate; for example, increasing the temperature increases the rate of collisions and, more significantly, increases the energy available to the particles to overcome the activation energy and react.

A catalyst increases the rate of a reaction but can be recovered, unchanged, at the end. Catalysts work by providing an alternative route for a reaction with a lower activation energy. Energy changes for uncatalysed and catalysed reactions have different reaction profiles.

The use of a catalyst can reduce the economic and environmental cost of an industrial process, leading to more sustainable ‘green’ chemical processes.

All the help links are at the end of C6.2

1. Be able to describe the effect on rate of reaction of changes in temperature, concentration, pressure, and surface area on rate of reaction.

LINKS: Endothermic and exothermic reactions and energy level diagrams. (C1)

Practical Work: Investigate the effect of temperature and concentration on rate of reactions.

Compare methods of following rate

Use the particle model to explain factors that affect rates of reaction

The use of catalysts supports more sustainable industrial processes.

2. Be able to explain the effects on rates of reaction of changes in temperature, concentration and pressure in terms of frequency and energy of collision between particles.

3. Be able to explain the effects on rates of reaction of changes in the size of the pieces of a reacting solid in terms of surface area to volume ratio.

4. Be able to describe the characteristics of catalysts and their effect on rates of reaction.

5. Be able to identify catalysts in reactions.

6. Be able to explain catalytic action in terms of activation energy.

Rate of reaction can be determined by measuring the rate at which a product is made or the rate at which a reactant is used. Some reactions involve a colour change or form a solid in a solution; the rate of these reactions can be measured by timing the changes that happen in the solutions by eye or by using apparatus such as a colorimeter. Reactions that make gases can be followed by measuring the volume of gas or the change in mass over time.

On graphs showing the change in a variable such as concentration over time, the gradient of a tangent to the curve is an indicator of rate of change at that time. The average rate of a reaction can be calculated from the time taken to make a fixed amount of product.

Enzymes are proteins that catalyse processes in living organisms. They work at their optimum within a narrow range of temperature and pH. Enzymes can be adapted and sometimes synthesised for use in industrial processes. Enzymes limit the conditions that can be used but this can be an advantage because if a process can be designed to use an enzyme at a lower temperature than a traditional process, this reduces energy demand.

7. Be able to suggest practical methods for determining the rate of a given reaction including:

(a) for reactions that produce gases:

(i) gas syringes or collection over water can be used to measure the volume of gas produced

(ii) mass change can be followed using a balance

(b) measurement of physical factors (HT only):

(i) colour change

(ii) formation of a precipitate

Practical work: Designing and carrying out investigations into rates.

Analysing and interpreting data.

Use of apparatus to make measurements.

Use of heating equipment.

Safe handling of chemicals.

Measuring rates of reaction using two different methods.

8. Be able to interpret rate of reaction graphs.

9. Be able to use arithmetic computation and ratios when measuring rates of reaction.

10. Be able to draw and interpret appropriate graphs from data to determine rate of reaction.

11. Be able to determine gradients of graphs as a measure of rate of change to determine rate

12. Be able to use proportionality when comparing factors affecting rate of reaction.

13. Be able to describe the use of enzymes as catalysts in biological systems and some industrial processes.

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

Particle model of the collision theory of chemical reaction rate factors

Effect of changing reactant concentration in solution

Effect of changing pressure in reacting gases

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

Effect of changing the temperature of reactants

Effect of using a catalyst in a chemical reaction

Catalysts and activation energy

Examples of graphs of rate data, interpretation

Enzymes and Biotechnology

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)


Chapter C6.3 What factors affect the yield of chemical reactions?

 (Revision for OCR GCSE 9–1 Twenty First Century Science Combined Science B chemistry 02, Topics for Chapter C6 "Making useful chemicals")

Industrial processes are managed to get the best yield as quickly and economically as possible. Chemists select the conditions that give the best economic outcome in terms of safety, maintaining the conditions and equipment, and energy use.

The reactions in some processes are reversible. This can be problematic in industry because the reactants never completely react to make the products. This wastes reactants and means that the products have to be separated out from the reactants, which requires extra stages and costs.

Data about yield and rate of chemical processes are used to choose the best conditions to make a product. On industrial scales, very high temperatures and pressures are expensive to maintain due to the cost of energy and because equipment may fail under extreme conditions. Catalysts can be used to increase the rate of reaction without affecting yield.

Chemical engineers choose the conditions that will make the process as safe and efficient as possible, reduce the energy costs and reduce the waste produced at all stages of the process.

1. Be able to recall that some reactions may be reversed by altering the reaction conditions including:

(a) reversible reactions are shown by the symbol

(b) reversible reactions (in closed systems) do not reach 100% yield

Links: Calculations of yields (C5.1)

Practical Work: Investigating reversible reactions.

Making predictions from data and graphs about yield of chemical products.

Considering the risks and costs of different operating conditions in an ammonia plant.

Practical work - Analyse and evaluate data about yield and rate of ammonia production.

Reversible Reactions - experiments described and explained

2. Be able to recall that dynamic equilibrium occurs when the rates of forward and reverse reactions are equal.

Reversible reactions and chemical equilibrium

3. (HT only) Be able to predict the effect of changing reaction conditions (concentration, temperature and pressure) on equilibrium position and suggest appropriate conditions to produce a particular product, including

(a) catalysts increase rate but do not affect yield

(b) the disadvantages of using very high temperatures or pressures

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

The Haber Synthesis of ammonia - nitrogen fixation


Chapter BCP7: Ideas about Science 

(For OCR GCSE (9–1) Twenty First Century Combined Science B chemistry exam papers)



Chapter IaS1 What needs to be considered when investigating a phenomenon scientifically?

The aim of science is to develop good explanations for natural phenomena. There is no single ‘scientific method’ that leads to good explanations, but scientists do have characteristic ways of working. In particular, scientific explanations are based on a cycle of collecting and analysing data. Usually, developing an explanation begins with proposing a hypothesis. A hypothesis is a tentative explanation for an observed phenomenon (“this happens because…”). The hypothesis is used to make a prediction about how, in a particular experimental context, a change in a factor will affect the outcome. A prediction can be presented in a variety of ways, for example in words or as a sketch graph. In order to test a prediction, and the hypothesis upon which it is based, it is necessary to plan an experimental strategy that enables data to be collected in a safe, accurate and repeatable way.

1. in given contexts use scientific theories and tentative explanations to develop and justify hypotheses and predictions.

Making and testing predictions:  trends and patterns in the Periodic Table (C2) and reactivity of metals (C3.2)

2. suggest appropriate apparatus, materials and techniques, justifying the choice with reference to the precision, accuracy and validity of the data that will be collected

3. recognise the importance of scientific quantities and understand how they are determined

4. identify factors that need to be controlled, and the ways in which they could be controlled

5. suggest an appropriate sample size and/or range of values to be measured and justify the suggestion

6. plan experiments or devise procedures by constructing clear and logically sequenced strategies to: - make observations - produce or characterise a substance - test hypotheses - collect and check data - explore phenomena

7. identify hazards associated with the data collection and suggest ways of minimizing the risk

8. use appropriate scientific vocabulary, terminology and definitions to communicate the rationale for an investigation and the methods used using diagrammatic, graphical, numerical and symbolic forms


Chapter IaS2 What processes are needed to draw conclusions from data?

The cycle of collecting, presenting and analysing data usually involves translating data from one form to another, mathematical processing, graphical display and analysis; only then can we begin to draw conclusions. A set of repeat measurements can be processed to calculate a range within which the true value probably lies and to give a best estimate of the value (mean). Displaying data graphically can help to show trends or patterns, and to assess the spread of repeated measurements. Mathematical comparisons between results and statistical methods can help with further analysis.

1. present observations and other data using appropriate formats

2. when processing data use SI units where appropriate (e.g. kg, g, mg; km, m, mm; kJ, J) and IUPAC chemical nomenclature unless inappropriate

3. when processing data use prefixes (e.g. tera, giga, mega, kilo, centi, milli, micro and nano) and powers of ten for orders of magnitude

4. be able to translate data from one form to another

5. when processing data interconvert units

6. when processing data use an appropriate number of significant figures

7. when displaying data graphically select an appropriate graphical form, use appropriate axes and scales, plot data points correctly, draw an appropriate line of best fit, and indicate uncertainty (e.g. range bars)

8. when analysing data identify patterns/trends, use statistics (range and mean) and obtain values from a line on a graph (including gradient, interpolation and extrapolation)

Chapter IaS2 What conclusions can we make from data?

Data obtained must be evaluated critically before we can make conclusions based on the results. There could be many reasons why the quality (accuracy, precision, repeatability and reproducibility) of the data could be questioned, and a number of ways in which they could be improved. Data can never be relied on completely because observations may be incorrect and all measurements are subject to uncertainty (arising from the limitations of the measuring equipment and the person using it). A result that appears to be an outlier should be treated as data, unless there is a reason to reject it (e.g. measurement or recording error)

9. in a given context evaluate data in terms of accuracy, precision, repeatability and reproducibility, identify potential sources of random and systematic error, and discuss the decision to discard or retain an outlier.

10. evaluate an experimental strategy, suggest improvements and explain why they would increase the quality (accuracy, precision, repeatability and reproducibility) of the data collected, and suggest further investigations.

Agreement between the collected data and the original prediction increases confidence in the tentative explanation (hypothesis) upon which the prediction is based, but does not prove that the explanation is correct. Disagreement between the data and the prediction indicates that one or other is wrong, and decreases our confidence in the explanation.

11. in a given context interpret observations and other data (presented in diagrammatic, graphical, symbolic or numerical form) to make inferences and to draw reasoned conclusions, using appropriate scientific vocabulary and terminology to communicate the scientific rationale for findings and conclusions.

12. explain the extent to which data increase or decrease confidence in a prediction or hypothesis.


Chapter IaS3 How are scientific explanations developed?

Scientists often look for patterns in data as a means of identifying correlations that can suggest cause-effect links – for which an explanation might then be sought.

The first step is to identify a correlation between a factor and an outcome. The factor may then be the cause, or one of the causes, of the outcome. In many situations, a factor may not always lead to the outcome, but increases the chance (or the risk) of it happening. In order to claim that the factor causes the outcome we need to identify a process or mechanism that might account for the observed correlation.

1. use ideas about correlation and cause to:

- identify a correlation in data presented as text, in a table, or as a graph

- distinguish between a correlation and a cause effect link

- suggest factors that might increase the chance of a particular outcome in a given situation, but do not invariably lead to it

- explain why individual cases do not provide convincing evidence for or against a correlation

- identify the presence (or absence) of a plausible mechanism as reasonable grounds for accepting (or rejecting) a claim that a factor is a cause of an outcome

Scientific explanations and theories do not ‘emerge’ automatically from data, and are separate from the data. Proposing an explanation involves creative thinking. Collecting sufficient data from which to develop an explanation often relies on technological developments that enable new observations to be made.

As more evidence becomes available, a hypothesis may be modified and may eventually become an accepted explanation or theory.

A scientific theory is a general explanation that applies to a large number of situations or examples (perhaps to all possible ones), which has been tested and used successfully, and is widely accepted by scientists. A scientific explanation of a specific event or phenomenon is often based on applying a scientific theory to the situation in question.

2. describe and explain examples of scientific methods and theories that have developed over time and how theories have been modified when new evidence became available .

Findings reported by an individual scientist or group are carefully checked by the scientific community before being accepted as scientific knowledge. Scientists are usually sceptical about claims based on results that cannot be reproduced by anyone else, and about unexpected findings until they have been repeated (by themselves) or reproduced (by someone else). Two (or more) scientists may legitimately draw different conclusions about the same data. A scientist’s personal background, experience or interests may influence his/her judgments. An accepted scientific explanation is rarely abandoned just because new data disagree with it. It usually survives until a better explanation is available.

3. describe in broad outline the ‘peer review’ process, in which new scientific claims are evaluated by other scientists.

Models are used in science to help explain ideas and to test explanations. A model identifies features of a system and rules by which the features interact. It can be used to predict possible outcomes. Representational models use physical analogies or spatial representations to help visualise scientific explanations and mechanisms. Descriptive models are used to explain phenomena. Mathematical models use patterns in data of past events, along with known scientific relationships, to predict behaviour; often the calculations are complex and can be done more quickly by computer. Models can be used to investigate phenomena quickly and without ethical and practical limitations, but their usefulness is limited by how accurately the model represents the real world.

4. use a variety of models (including representational, spatial, descriptive, computational and mathematical models) to:

- solve problems

- make predictions

- develop scientific explanations and understanding

- identify limitations of models.


Chapter IaS4 How do science and technology impact society?

Science and technology provide people with many things that they value, and which enhance their quality of life. However some applications of science can have unintended and undesirable impacts on the quality of life or the environment. Scientists can devise ways of reducing these impacts and of using natural resources in a sustainable way (at the same rate as they can be replaced).

Everything we do carries a certain risk of accident or harm. New technologies and processes can introduce new risks.

The size of a risk can be assessed by estimating its chance of occurring in a large sample, over a given period of time.

To make a decision about a course of action, we need to take account of both the risks and benefits to the different individuals or groups involved. People are generally more willing to accept the risk associated with something they choose to do than something that is imposed, and to accept risks that have short-lived effects rather than long-lasting ones. People’s perception of the size of a particular risk may be different from the statistically estimated risk. People tend to over-estimate the risk of unfamiliar things (like flying as compared with cycling), and of things whose effect is invisible or long-term (like ionising radiation).

Some forms of scientific research, and some applications of scientific knowledge, have ethical implications. In discussions of ethical issues, a common argument is that the right decision is one which leads to the best outcome for the greatest number of people. Scientists must communicate their work to a range of audiences, including the public, other scientists, and politicians, in ways that can be understood. This enables decision-making based on information about risks, benefits, costs and ethical issues.

1. describe and explain everyday examples and technological applications of science that have made significant positive differences to people’s lives.

2. identify examples of risks that have arisen from a new scientific or technological advance

3. for a given situation:

- identify risks and benefits to the different individuals and groups involved

- discuss a course of action, taking account of who benefits and who takes the risks

- suggest reasons for people’s willingness to accept the risk

- distinguish between perceived and calculated risk

4. suggest reasons why different decisions on the same issue might be appropriate in view of differences in personal, social, economic or environmental context, and be able to make decisions based on the evaluation of evidence and arguments.

5. distinguish questions that could in principle be answered using a scientific approach, from those that could not; where an ethical issue is involved clearly state what the issue is and summarise the different views that may be held.

6. explain why scientists should communicate their work to a range of audiences.


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