OCR GCSE SCIENCES B (21st Century Science)

ALL MY GCSE CHEMISTRY REVISION NOTES

Revision summary help for the 9-1 OCR 21st Century Science GCSE CHEMISTRY B Exam Papers - learning objectives C4-C6

OCR Level 1/2 GCSE (Grade 9-1) in Chemistry B (Twenty First Century Science) (J258) - OCR 21st Century GCSE Grade 9-1 chemistry B revision summaries for Chapter C4, Chapter C5 and Chapter C6

LINK for OCR Twenty First Century 9-1 GCSE CHEMISTRY chapt's C1-C3

from quiz for OCR GCSE 21st Century Combined Sci. chemistry C4-C6

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

INDEX for all links

These are my NEW revision summaries for Y10 starting in September 2016, first exams from May-June 2018 onwards. ALL my unofficial GCSE (Grade 9-1) revision help is based on the NEW 2016 official OCR 9-1 GCSE Twenty First Century Science B chemistry/science specifications. Make sure you know whether you are doing separate science OCR 9-1 GCSE Twenty First Century CHEMISTRY B OR OCR 9-1 GCSE Twenty First Century Combined Science B chemistry.

PAST PAPERS    The Google [SEARCH] box at the bottom of the page should also prove useful

(HT only) means higher tier only (NOT FT foundation tier) and (GCSE chemistry only) means for the separate science, NOT for Combined Science chemistry

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.



Syllabus-specification CONTENT INDEX of revision summary notes

Be aware that both Paper 1 "Breadth in Chemistry" and Paper 2 "Depth in Chemistry" assess content from ALL chapters !!!

What's assessed in these papers?

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?

Chapter C2.5 What are the properties of transition metals?

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 What are the different types of polymers?

Revision summary Chapter C4.3 How do bonding and structure affect properties of materials?

Revision summary Chapter C4.4 Why are nanoparticles so useful?

Revision summary Chapter C4.5 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 do chemists find the composition of unknown samples?

Revision summary Chapter C5.3 How are the amounts of substances in reactions calculated?

Revision summary Chapter C5.4 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?

Revision summary Chapter C6.4 How are chemicals made on an industrial scale?

SUMMARY Chapter C7: 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?


Chapter C4:   (For OCR GCSE (9–1) Twenty First Century Science CHEMISTRY B exam papers)



Chapter C4 Material choices  (For OCR GCSE (9–1) Twenty First Century Science CHEMISTRY B exam papers)

Quiz on selected aspects of OCR Twenty First Century GCSE 9-1 Chemistry 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 B)

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

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


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

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.

The range of uses of metals has been extended by the development of alloys. Alloys have different properties to pure metals due to the disruption of the metal lattice by atoms of different sizes. Chemists can match an alloy to the specification of properties for a new product.

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.

3. (GCSE Chemistry only) Be able to describe the composition of some important alloys in relation to their properties and uses, including steel.

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


Chapter C4.2 What are the different types of polymers? (GCSE Chemistry only)

Polymers are long chain molecules that occur naturally and can also be made synthetically. Monomers based on alkenes from crude oil can be used to make a wide range of addition polymers that are generally known as ‘plastics’. Addition polymers form when the double bonds in small molecules open to join the monomers together into a long chain.

(HT only) Condensation polymers were developed to make materials that are substitutes for natural fibres such as wool and silk.

(HT only) Condensation polymers usually form from two different monomer molecules which contain different functional groups. The OH group from a carboxylic acid monomer and an H atom from another monomer join together to form a water molecule. Monomers that react with carboxylic acid monomers include alcohols (to make polyesters) and amines (to make polyamides). To make a polymer, each monomer needs two functional groups. The structure of the repeating unit of a condensation polymer can be worked out from the formulae of its monomers and vice versa.

1. Be able to recall the basic principles of addition polymerisation by reference to the functional group in the monomer and the repeating units in the polymer.

Practical work: Cracking poly(ethene) and testing the gas for unsaturation.

Testing properties of different polymer fibres.

2. Be able to deduce the structure of an addition polymer from a simple monomer with a double bond and vice versa.

3. (HT only) Be able to explain the basic principles of condensation polymerisation by reference to the functional groups of the monomers, the minimum number of functional groups within a monomer, the number of repeating units in the polymer, and simultaneous formation of a small molecule, You are not expected to recall the formulae of dicarboxylic acid, diamine and diol monomers.

Help links for C4.2 1. to 3.

Addition polymers, plastics, uses and problems

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

Many natural polymers are essential to life. Genes are made of DNA, a polymer of four nucleotide monomers. Proteins (which are similar in structure to polyamides) are polymers of amino acids. Carbohydrates, including starch and cellulose, are polymers of sugars.

4. Be able to recall that DNA is a polymer made from four different monomers called nucleotides and that other important naturally-occurring polymers are based on sugars and amino-acids

Syllabus links: Structure and function of DNA, and protein synthesis (B1.1) The synthesis and breakdown of carbohydrates and proteins (B3.3) Practical work Breaking down starch using an enzyme and using food tests to identify starch and sugars

Natural Molecules - carbohydrates - sugars - natural polymers - starch and DNA

Amino acids - natural polymers - proteins/polypeptides, enzymes & chromatography


C4.3 How do bonding and structure affect properties of materials? (GCSE Combined Science Chapter 4.2)

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 C4.4 Why are nanoparticles so useful?

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 C4.5 What happens to products at the end of their useful life?

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. Barrier methods to prevent corrosion extend the useful life of metal products, which is good for consumers and has a positive outcome in terms of the life cycle assessment.

Sacrificial protection uses a more reactive metal such as zinc to oxidise in preference to iron. This continues to prevent corrosion even if the coating on the metal is damaged.

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.

1. Be able to describe the conditions which cause corrosion and the process of corrosion, and explain how mitigation is achieved by creating a physical barrier to oxygen and water and by sacrificial protection.

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

Use life cycle assessments to compare the sustainability of products and processes.

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

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

3./2. 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

4./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

5./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

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

7./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:   (For OCR GCSE (9–1) Twenty First Century Science CHEMISTRY B exam papers)



Chapter C5 Chemical analysis  (For OCR GCSE (9–1) Twenty First Century Science CHEMISTRY B exam papers)

Quiz on selected aspects of OCR Twenty First Century GCSE 9-1 Chemistry B 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 Chemistry B)

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

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


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

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 do chemists find the composition of unknown samples? (GCSE Chemistry only)

Chemists use qualitative analysis to identify components in a sample. The procedures have a wide range of applications, including testing chemicals during manufacturing process, testing mineral samples, checking for toxins in waste, environmental testing of water, testing soils. Chemists use sampling techniques to make sure that the samples used for the analysis are representative and will identify any variations in the bulk of the material that is represented in the analysis (IaS1). Laboratory analysis can be used to identify the metal cations and the anions in salts. Cations can be identified using flame tests or by adding dilute sodium hydroxide. Anions can be identified using a range of dilute reagents. Instrumental analysis is widely used in research and in industry. Emission spectroscopy is a technique which relies on looking at the spectrum of light emitted from a hot sample. Each element gives a unique pattern of lines. Elements can be identified by matching the patterns and wavelengths of lines to reference data from known elements. Emission spectroscopy is used to identify elements in stars and in substances such as steel in industry. Instrumental analysis is preferred due to its greater sensitivity, speed and accuracy. Data is automatically recorded. However, the technology is expensive and is not as freely available as the standard glassware used in laboratory analysis. (help links at the end of section C5.2)

1. Be able to describe the purpose of representative sampling in qualitative analysis

Symbols, formulae and ionic equations.

Suggest equipment and techniques and a strategy to carry out qualitative analysis

2. Be able to interpret flame tests to identify metal ions, including the ions of lithium, sodium, potassium, calcium and copper.

3. Be able to describe the technique of using flame tests to identify metal ions.

4. Be able to describe tests to identify aqueous cations and aqueous anions and identify species from test results including:

(a) tests and expected results for metal ions in solution by precipitation reactions using dilute sodium hydroxide (calcium, copper, iron(II), iron(III), zinc)

(b) tests and expected results for carbonate ions (using dilute acid)

(c) chloride, bromide and iodide ions (using acidified dilute silver nitrate)

(d) sulfate ions (using acidified dilute barium chloride or acidified barium nitrate)

5. Be able to interpret an instrumental result for emission spectroscopy given appropriate data in chart or tabular form, when accompanied by a reference set in the same form.

6. Be able to describe the advantages of instrumental methods of analysis (sensitivity, accuracy and speed).

7. Be able to interpret charts, particularly in spectroscopy.

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

Summary of 'GCSE' tests for gases and ions including equations

Instrumental Methods of Chemical Analysis

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


Chapter C5.3 How are the amounts of substances in reactions calculated?

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

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.

The rest of Chapter C5.3 is for separate science GCSE Chemistry, NOT combined science.

11. (GCSE Chemistry only) Be able to calculate the theoretical amount of a product from a given amount of reactant.

12. (GCSE Chemistry only) Be able to calculate the percentage yield of a reaction product from the actual yield of a reaction.

13. (GCSE Chemistry only) Be able to suggest reasons for low yields for a given procedure.

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

One mole of any gas has the same volume of 24 dm3 at room temperature and pressure. So the number of moles of molecules in a known volume of gas can be calculated, using the formula:

number of moles of gas = volume of gas in sample (dm3) / 24 (dm3)

For reactions involving only gases, the relative volumes of reactant or product gases can be worked out directly from the equation. For reactions with substances in a mixture of states, calculations may involve using both masses and gas volumes to calculate amounts of products and reactants.

14.  (GCSE Chemistry HT only) Be able to describe the relationship between molar amounts of gases and their volumes and vice versa, and calculate the volumes of gases involved in reactions, using the molar gas volume at room temperature and pressure (assumed to be 24dm3).

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

Molar gas volume type in answer QUIZ

Molar gas volume multiple choice QUIZ

Reacting gas volume ratios, Avogadro's Law and Gay-Lussac's Law (ratio of gaseous reactants-products)

Reacting volumes type in answer QUIZ

Reacting volumes multiple choice QUIZ


Chapter C5.4 How are the amounts of chemicals in solution measured?

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. (GCSE Chemistry only) Be able to identify the difference between qualitative and quantitative analysis.

2./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

3./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

4./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

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

6./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

7./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.

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

9. (GCSE Chemistry only) Be able to explain the relationship between the volume of a solution of known concentration of a substance and the volume or concentration of another substance that react completely together.

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

Titration type in answer QUIZ

Titration multiple choice QUIZ


Chapter C6:   (For OCR GCSE (9–1) Twenty First Century Science CHEMISTRY B exam papers)



Chapter C6 Making useful chemicals  (For OCR GCSE (9–1) Twenty First Century Science CHEMISTRY B exam papers)

Quiz on selected aspects of OCR Twenty First Century GCSE 9-1 Chemistry B 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 Chemistry B)

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

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


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

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).

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?

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. (GCSE Chemistry HT only) Be able to interpret graphs of reaction conditions versus rate (an understanding of orders of reaction is not required)

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

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

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

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

14./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?

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 C6.4 How are chemicals made on an industrial scale?

Nitrogen, phosphorus and potassium are essential plant nutrient elements; they are lost from the soil when crops use them for growth and then are harvested. Fertilisers are added to the soil to replace these essential elements.

The world demand for food cannot be met without the use of synthetic fertilisers. Natural fertilisers are not available in large enough quantities, their supply is difficult to manage and transport and their composition is variable. However, fertilisers can cause environmental harm when overused; if they are washed into rivers they cause excessive weed growth, which can lead to the death of the organisms that live there.

Ammonia is one of the most important compounds used to make synthetic fertilisers. Ammonia is made in the Haber process, which involves a reversible reaction.

(HT only) To get the greatest output as quickly and economically as possible chemical engineers consider the rate and the position of equilibrium for the reaction. In practice, industrial processes rarely reach equilibrium. In the Haber process unreacted reactants are continuously separated from the ammonia and recycled so that the nitrogen and hydrogen are not wasted.

Industrial processes need to be as economically profitable as possible. Atom economy is an indicator of the amount of useful product that is made in a reaction. This is a theoretical value based on the reaction equation and is used alongside data about yields and efficiency when processes are evaluated.

(HT only) Modern processes incorporate ‘green chemistry’ ideas, to provide a sustainable approach to production. Sustainability is a measure of how a process is able to meet current demand without having a long term impact on the environment. Reactions with high atom economy are more. Other issues which affect the sustainability of a process include; whether or not the raw materials are renewable; the impact of other competing uses for the same raw materials; the nature and amount of by-products or wastes; the energy inputs or outputs.

Synthetic fertilisers contain salts that are made in acid-base reactions and can be synthesised on a laboratory scale. Scaling up of fertiliser manufacture for industrial production uses some similar processes to the laboratory preparation, but these are adapted to handle the much larger quantities involved.

1. Be able to recall the importance of nitrogen, phosphorus and potassium compounds in agricultural production

Links: Haber Process (C4.3)

Practical Work - Laboratory preparation and purification of salts that are used as fertilisers.

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

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

The production of fertilisers to enhance the quality of people’s lives.

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

The Haber Synthesis of ammonia

Computer simulation of ammonia yield versus conditions (it might work?)

Manufacture and uses of fertilisers, preparation of ammonium salts, NPK fertilisers-environmental problems

2. Be able to explain the importance of the Haber process in agricultural production and the benefits and costs of making and using fertilisers, including:

(a) the balance between demand and supply of food Worldwide

(b) the sustainability and practical issues of producing and using synthetic and natural fertilisers on a large scale

(c) the environmental impact of over-use of synthetic fertilisers (eutrophication)

Manufacture and uses of fertilisers, preparation of ammonium salts, NPK fertilisers-environmental problems

3. (HT only) Be able to explain how the commercially used conditions for the Haber process are related to the availability and cost of raw materials and energy supplies, control of equilibrium position and rate including:

(a) the sourcing of raw materials and production of the feedstocks; nitrogen (from air), and hydrogen (from natural gas and steam)

(b) the effect of a catalyst, temperature and pressure on the yield and rate of the reaction

(c) the separation of the ammonia and recycling of unreacted nitrogen and hydrogen

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

The Haber Synthesis of ammonia - nitrogen fixation

4. (HT only) Be able to explain the trade-off between rate of production of a desired product and position of equilibrium in some industrially important processes.

The Haber Synthesis of ammonia

5. Be able to define the atom economy of a reaction.

6. Be able to calculate the atom economy of a reaction to form a desired product from the balanced equation using the formula:

atom economy = mass of atoms in desired product / total mass of atoms in reactants

Atom economy definition and calculations

7. Be able to use arithmetic computation when calculating atom economy.

8. (HT only) Be able to explain why a particular reaction pathway is chosen to produce a specified product given appropriate data such as atom economy (if not calculated), yield, rate, equilibrium position, usefulness of by-products and evaluate the sustainability of the process.

The Principles & Practice of Chemical Production - Synthesising Molecules

Any one compound used in fertilisers can often be made using several different processes. An example is the manufacture of ammonium sulfate. The synthesis stage of manufacture could be the same as the process used in the laboratory; but alternatively a manufacturer might make use of bi-product or waste products from other production processes. Finding uses for bi-products is an important factor in ensuring the sustainability of industrial processes.

Laboratory scale procedures such as choosing reactants, synthesis, monitoring the reaction, separation techniques, disposal of waste and testing of purity have parallel counterparts in the industrial process.

9. Be able to describe the industrial production of fertilisers as several integrated processes using a variety of raw materials and compare with laboratory syntheses. including:

(a) demand for fertilisers (including ammonium sulfate) is often met from more than one process

(b) some fertilisers are made as a bi-product or waste product of another process e.g. sewage sludge

(c) process flow charts are used to summarise industrial processes and give information about raw materials, stages in the process, products, by-products and waste

(d) lab processes prepare chemicals in batches, industrial processes are usually continuous.

Industrial processes can be modelled in the laboratory and using computers before making decisions about full scale production.

Manufacture and uses of fertilisers, preparation of ammonium salts, NPK fertilisers-environmental problems

Computer simulation of ammonia yield versus condition

10. Be able to compare the industrial production of fertilisers with laboratory syntheses of the same products

Pages covering general ideas

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

Products of the Chemical & Pharmaceutical Industries & Impact on Us

The Principles & Practice of Chemical Production - Synthesising Molecules


Chapter C7: Ideas about Science  (For OCR GCSE (9–1) Twenty First Century Science CHEMISTRY B 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 conclusions can we make 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)

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.

Drawing conclusions from data - patterns in the periodic table (C2) and properties of polymers (C4.3)

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.

Positive applications of science: catalytic converters, low sulfur petrol and gas scrubbers (C1.1), fuel cells (C1.2), increasing supply of potable water (C1.4), uses of metals (C2.5, C3.1), catalysts (C2.5, C6.2), cracking (C3.4), many new materials (C4), salts (C6.1), fertilisers (C6.4)

Sustainability: energy demands use of fuels (C1.2), use of crude oil (C3.4), reducing corrosion (C4.5), life cycle

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.


Chapter C8 Practical Skills

-


PAST PAPERS  (For OCR GCSE (9–1) Twenty First Century Science CHEMISTRY B exam papers)



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