Key term
OCR GCSE Chemistry A J248
Chemical Reactions
Topic overviewWriting formulae of elements and compoundsBalanced equations, and deducing formulae from ionsState symbols in equationsConservation of mass, and changes of mass in open systemsExothermic and endothermic reactions, and reaction profilesActivation energy and why reactions need itOxidation and reduction in terms of oxygenAcids, alkalis and neutralisationThe ionic equation for neutralisation, and reactions of acidsThe pH scale, acidity and alkalinityMeasuring pH with indicators and pH metersProducts at the electrodes, and molten ionic compoundsElectrolysis of aqueous solutionsInert and non-inert electrodes
Elements, Compounds and Mixtures
Topic overviewPurity, and melting point dataRelative formula mass and empirical formulaeFormulations, and separating mixturesPaper and thin layer chromatographyInterpreting chromatograms and Rf valuesChoosing a purification methodMetals and non-metals in the Periodic TableElectron arrangement and position in the Periodic TableIonic, covalent and metallic bonding comparedDot and cross diagrams, and the limits of modelsReactions, electron arrangement and Mendeleev's tableCarbon's four bonds, and the variety of organic compoundsDiamond, graphite, fullerenes and grapheneBond strength, intermolecular forces and predicting stateBulk properties of ionic, molecular and giant structuresNanoparticles: size and surface area to volumeUses and risks of nanoparticulate materials
Global Challenges
Topic overviewExtracting metals by reduction and by electrolysisThe Haber process and fertiliser productionNitrogen, phosphorus and potassium in agricultureLife cycle assessmentRecycling, and the decisions behind itAlloys, and the corrosion of metalsComparing glass, ceramics, polymers, composites and metalsFunctional groups and homologous seriesPredicting the products of organic reactionsAddition polymerisationDNA and other natural polymersFractional distillation of crude oilThe fractions, and crude oil as a feedstockDependence on hydrocarbons, and crackingChemical cells and fuel cellsThe Earth's early atmosphere, and how oxygen developedThe greenhouse effect, and evidence for climate changeEffects of carbon dioxide and methane, and air pollutantsProducing potable water
Monitoring and Controlling Chemical Reactions
Topic overviewCarrying out an acid–alkali titrationTheoretical mass and percentage yieldAtom economy and its calculationMeasuring the rate of a reaction, and rate graphsFactors affecting rate, and collision theorySurface area and rateCatalysts and how they workReversible reactions and dynamic equilibriumActivation energy, and enzymes as catalysts
Particles
Predicting and Identifying Reactions
Topic overviewGroups 1, 7 and 0, and why they behave as they doTransition metalsPredicting reactivity from the Periodic TableReactivity of metals with water and acidsTests for oxygen, hydrogen, carbon dioxide and chlorineTests for aqueous cations and anionsFlame tests, and identifying metal ionsIdentifying a species from test resultsInstrumental methods of analysis
Monitoring and Controlling Chemical Reactions
- 9 subtopics
- 27 things to know
- Paper 2
What Monitoring and Controlling Chemical Reactions covers
Monitoring and Controlling Chemical Reactions is examined in Chemistry A Paper 2. It covers titration technique; theoretical mass and percentage yield; atom economy; measuring the rate of a reaction and rate graphs; factors affecting rate and collision theory; surface area and rate; catalysts and how they work; reversible reactions and dynamic equilibrium; and activation energy and enzymes as catalysts.
Where it is assessed
Paper 2
Chemistry A Paper 2: 1 hour 45 minutes, 90 marks, 50% of the GCSE.
Check the OCR specification ↗The 9 subtopics
Each one has its own page.
- Carrying out an acid–alkali titrationThe pipette, burette and white tile used in a titration, what the end point is, the colour changes of phenolphthalein and methyl orange, reading a burette at the meniscus, why a rough titration comes first and the flask is swirled, and what concordant titres are and why only they are averaged.Open →
- Theoretical mass and percentage yieldWhat a theoretical mass is and the three steps to calculate it, worked examples from calcium carbonate, magnesium, nitrogen and hydrogen, the limiting reactant, percentage yield calculations, and why yields fall short of 100%.Open →
- Atom economy and its calculationWhat atom economy is and how it is calculated, when it reaches 100%, why manufacturers want it high and how it differs from percentage yield, what happens to by-products and how selling them helps, why the reactant total is used, and worked calculations for calcium oxide, iron, ammonia, hydrogen, oxygen and magnesium chloride.Open →
- Measuring the rate of a reaction, and rate graphsWhat rate means, following a reaction with a gas syringe, a balance, a disappearing cross, a colorimeter or a pH probe, the units of rate, and reading the gradient of a rate graph.Open →
- Factors affecting rate, and collision theoryHow temperature, concentration, pressure and surface area affect rate, why concentration changes the speed but not the amount of product, the rough doubling for each 10 °C rise, how rate changes during a reaction, the two conditions for a successful collision, explaining each factor with collision theory and activation energy, reading rate ∝ 1/t, and planning, evaluating and improving the sodium thiosulfate investigation.Open →
- Surface area and rateHow breaking a solid up raises its surface area to volume ratio, why powders react faster, the cube calculations, the flour dust hazard, and comparing the graphs for powder and lumps.Open →
- Catalysts and how they workWhat a catalyst is, why its mass is unchanged and it sits above the arrow, why catalysts are specific and used in industry, and the catalysts for hydrogen peroxide, ammonia and sulfuric acid.Open →
- Reversible reactions and dynamic equilibriumWhat a reversible reaction is and its symbol, why the reverse of an exothermic reaction is endothermic, heating hydrated copper(II) sulfate and testing for water, heating ammonium chloride, the nitrogen and hydrogen that form ammonia, what dynamic equilibrium and a closed system are, what the position of equilibrium means, and how the forward and reverse rates change until equilibrium is reached.Open →
- Activation energy, and enzymes as catalystsHow a catalyst gives a pathway with a lower activation energy, reaction profiles for catalysed reactions, why lowering the activation energy speeds a reaction, calculating activation energies and energy changes from profiles, what enzymes are and why organisms need them, denaturing by heat and pH, enzyme specificity, uses in brewing and washing powders, and how enzymes compare with metal catalysts.Open →
What you need to know
Answer each one before you reveal it.
Your recallNot started
Key term
When is atom economy 100%, why do manufacturers prefer a high atom economy, and how does atom economy differ from percentage yield?
Key term
In a titration, which piece of apparatus is used to measure the accurate fixed volume of solution placed in the conical flask?
Process
State the three steps used to calculate the theoretical mass of a product from a given mass of reactant.
Key term
Describe the effect of raising the temperature on the rate of a reaction.
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Explain why a powdered solid reacts faster than the same mass of the solid in one large lump.
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Explain why only a small mass of catalyst is needed to convert a very large mass of reactant.
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What symbol is used in an equation to show that a reaction is reversible?
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Describe how the reaction profile for a catalysed reaction differs from that of the same reaction without a catalyst.
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In a titration, which piece of apparatus delivers the second solution in a measured but variable volume?
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If one reactant is present in excess, which reactant must the theoretical mass be calculated from?
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Under what circumstances does a reaction have an atom economy of 100%?
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In general terms, what two quantities can be followed over time to measure the rate of a reaction?
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Describe the effect of increasing the concentration of a reactant in solution on the rate of a reaction.
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Which particles of a solid reactant are able to take part in a reaction with a solution?
Key term
Describe how you could show experimentally that a substance added to a reaction acted as a catalyst.
Key term
How is anhydrous copper(II) sulfate used as a test for water?
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Explain why lowering the activation energy makes a reaction faster.
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Name two indicators used in acid–alkali titrations and give the colour change of each as acid is added to alkali.
Key term
How is the percentage yield of a reaction calculated?
Process
Give two reasons why a manufacturer prefers a process with a high atom economy.
Key term
Suggest how a balance can be used to measure the rate of a reaction that releases a gas, and explain why the mass changes.
Key term
Describe the effect of increasing the pressure on a reaction between gases.
Numbers
A cube of solid has sides of 3 cm. Calculate its surface area, its volume and its surface area to volume ratio.
Key term
Name a metal used as the catalyst in a car's catalytic converter.
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Name the two gases that combine reversibly to make ammonia.
Key term
A reaction profile shows the reactants at 100 kJ/mol, the peak at 180 kJ/mol and the products at 40 kJ/mol. Calculate the activation energy and the overall energy change.
Take Monitoring and Controlling Chemical Reactions further
The same content, four other ways.
Commonly confused
Pairs that lose marks when they are blurred together.
Percentage yield vs Atom economy
Percentage yield: actual mass of product divided by the theoretical mass, times 100. Atom economy: proportion of the reactant mass that ends up as the desired product.
Dynamic equilibrium vs Reversible reaction
Dynamic equilibrium: closed-system state where forward and reverse rates are equal. Reversible reaction: products can react together to re-form the original reactants.
Concordant titres vs Rough titration
Concordant titres: repeat readings that agree within 0.10 cm³ of each other. Rough titration: first quick run to locate the end point.
Questions from this topic
Each one with the model answer underneath.
- 1
In a titration, which piece of apparatus is used to measure the accurate fixed volume of solution placed in the conical flask?
Model answer
A pipette, used with a safety filler, measures a fixed volume such as 25.0 cm³ into the conical flask.
- 2
In a titration, which piece of apparatus delivers the second solution in a measured but variable volume?
Model answer
A burette, which is filled to the zero mark and read before and after the solution is run in.
- 3
What is meant by the end point of a titration?
Model answer
It is the point at which the indicator changes colour permanently, showing that the two solutions have just reacted completely.
- 4
Why is a white tile placed under the conical flask during a titration?
Model answer
It makes the colour change of the indicator much easier to see, so the end point is judged more accurately.
- 5
Name two indicators used in acid–alkali titrations and give the colour change of each as acid is added to alkali.
Model answer
Phenolphthalein changes from pink to colourless, and methyl orange changes from yellow to red.
- 6
How should a burette be read correctly?
Model answer
Read it at eye level from the bottom of the meniscus, to the nearest 0.05 cm³.
What is inside Levo
Six ways to work the same material.
Monitoring and Controlling Chemical Reactions revision questions
- What does Monitoring and Controlling Chemical Reactions cover in OCR GCSE Chemistry A?
- 9 subtopics: carrying out an acid–alkali titration, theoretical mass and percentage yield, atom economy and its calculation, measuring the rate of a reaction, and rate graphs, factors affecting rate, and collision theory, surface area and rate, catalysts and how they work, reversible reactions and dynamic equilibrium and activation energy, and enzymes as catalysts. Each one has its own page with questions and model answers.
- How is Monitoring and Controlling Chemical Reactions organised?
- By the OCR J248 specification, subtopic by subtopic, so it matches the order you are taught it in.
Every question in Monitoring and Controlling Chemical Reactions, on a schedule.
Attempt a question from memory, write the correct version, then attempt it again. Levo records the jump between your first attempt and your last, and brings each question back on the day you are due to forget it.
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