Key term
OCR GCSE Chemistry A J248
Chemical Reactions
Topic overviewWriting formulae of elements and compoundsBalanced equations, and deducing formulae from ionsIonic equations, and state symbolsThe mole and the Avogadro constantConservation of mass, and changes of mass in open systemsStoichiometry, and calculating reacting massesExothermic and endothermic reactions, and reaction profilesActivation energy, and bond energy calculationsOxidation and reduction, by oxygen and by electronsAcids, alkalis and neutralisationThe ionic equation for neutralisation, and reactions of acidsDilute and concentrated, weak and strongThe pH scale, and hydrogen ion concentrationpH as a factor of ten, and measuring pHProducts 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 electrolysisBiological methods of metal extractionRate against yield in industry, and reaction conditionsThe 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 polymerisationCondensation polymerisation, and making a polymerDNA 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 overviewConcentration in mol/dm³, and titrationTitration calculations, and the mass of a soluteMolar gas volume and the volumes of gasesTheoretical mass and percentage yieldAtom economy, and choosing a reaction pathwayMeasuring the rate of a reaction, and rate graphsFactors affecting rate, and collision theorySurface area and rateCatalysts and how they workReversible reactions and dynamic equilibriumChanging the conditions of an 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
- 12 subtopics
- 36 things to know
- Paper 4
What Monitoring and Controlling Chemical Reactions covers
Monitoring and Controlling Chemical Reactions is examined in Chemistry A Paper 4. It covers concentration in mol/dm³ and titration; titration calculations and the mass of a solute; molar gas volume and the volumes of gases; theoretical mass and percentage yield; atom economy and choosing a reaction pathway; 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; changing the conditions of an equilibrium; and activation energy and enzymes as catalysts.
Where it is assessed
Paper 4
Chemistry A Paper 4: 1 hour 45 minutes, 90 marks, 50% of the GCSE.
Check the OCR specification ↗The 12 subtopics
Each one has its own page.
- Concentration in mol/dm³, and titrationWhat concentration in mol/dm³ means and how it relates to moles and volume, converting cm³ to dm³, calculating concentrations and masses and converting from g/dm³, the effect of dilution, the pipette, burette, white tile and indicators used in a titration, what the end point is, reading a burette, rough titrations and concordant titres.Open →
- Titration calculations, and the mass of a soluteThe three steps from titration results to an unknown concentration, worked titration calculations including a 1:2 ratio, averaging concordant titres, converting mol/dm³ to g/dm³, and mass, volume and concentration calculations.Open →
- Molar gas volume and the volumes of gasesThe 24 dm³ molar gas volume at room temperature and pressure, why every gas occupies the same volume, converting between moles and volume, and calculating gas volumes from reacting masses and equations.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 choosing a reaction pathwayWhat 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, worked calculations for calcium oxide, iron, ammonia, hydrogen, oxygen and magnesium chloride, and choosing a reaction pathway by weighing atom economy, yield, rate, equilibrium position and useful by-products.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 →
- Changing the conditions of an equilibriumLe Chatelier’s principle, and the effect on the position of equilibrium of changing concentration, removing a product, raising or lowering the temperature, and changing the pressure, with the compromise conditions for ammonia and sulfur trioxide.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
For the exothermic equilibrium 2SO₂ + O₂ ⇌ 2SO₃, why is a moderately high temperature used and what does raising the pressure do?
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When is atom economy 100%, why do manufacturers prefer a high atom economy, and how does atom economy differ from percentage yield?
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State the relationship between concentration, number of moles of solute and volume of solution.
Process
State the three steps used to work out an unknown concentration from titration results.
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Express the volume of one mole of gas at room temperature and pressure in cm³.
Process
State the three steps used to calculate the theoretical mass of a product from a given mass of reactant.
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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.
Numbers
How do you convert a volume measured in cm³ into dm³?
Numbers
How do you calculate the number of moles in a solution from its concentration in mol/dm³ and its volume in cm³?
Numbers
How do you calculate the number of moles of a gas from its volume in dm³ at room temperature and pressure?
Key term
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?
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Describe how you could show experimentally that a substance added to a reaction acted as a catalyst.
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How is anhydrous copper(II) sulfate used as a test for water?
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State the principle used to predict how the position of an equilibrium responds to a change in conditions.
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Explain why lowering the activation energy makes a reaction faster.
Numbers
A solution contains 0.50 mol of solute in 250 cm³ of solution. Calculate its concentration in mol/dm³.
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Why must the balanced equation be used in a titration calculation rather than assuming the moles are equal?
Numbers
How do you calculate the volume of a gas at room temperature and pressure from the number of moles?
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How is the percentage yield of a reaction calculated?
Process
Give two reasons why a manufacturer prefers a process with a high atom economy.
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Suggest how a balance can be used to measure the rate of a reaction that releases a gas, and explain why the mass changes.
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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.
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Predict the effect of increasing the concentration of a reactant on the position of an equilibrium.
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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
What does the concentration of a solution measured in mol/dm³ tell you?
Model answer
It tells you how many moles of solute are dissolved in each cubic decimetre of solution.
- 2
State the relationship between concentration, number of moles of solute and volume of solution.
Model answer
Concentration in mol/dm³ equals the number of moles of solute divided by the volume of the solution in dm³.
- 3
How do you convert a volume measured in cm³ into dm³?
Model answer
Divide the volume in cm³ by 1000.
- 4
A solution contains 0.50 mol of solute in 250 cm³ of solution. Calculate its concentration in mol/dm³.
Model answer
250 cm³ is 0.250 dm³, so the concentration is 0.50 ÷ 0.250 = 2.0 mol/dm³, given to 2 significant figures.
- 5
4.0 g of sodium hydroxide, relative formula mass 40, is dissolved to make 500 cm³ of solution. Calculate the concentration in mol/dm³.
Model answer
4.0 ÷ 40 = 0.10 mol of solute in 0.500 dm³, so the concentration is 0.10 ÷ 0.500 = 0.20 mol/dm³, given to 2 significant figures.
- 6
Calculate the mass of sodium hydroxide, relative formula mass 40, in 100 cm³ of a solution of concentration 2.00 mol/dm³.
Model answer
2.00 × 0.100 = 0.200 mol, and 0.200 × 40 = 8.00 g, given to 3 significant figures.
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Monitoring and Controlling Chemical Reactions revision questions
- What does Monitoring and Controlling Chemical Reactions cover in OCR GCSE Chemistry A?
- 12 subtopics: concentration in mol/dm³, and titration, titration calculations, and the mass of a solute, molar gas volume and the volumes of gases, theoretical mass and percentage yield, atom economy, and choosing a reaction pathway, 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, changing the conditions of an 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.
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