Monitoring and Controlling Chemical Reactions | OCR GCSE Chemistry A, Foundation tier (J248)
Monitoring and Controlling Chemical Reactions
- 145 questions
- 9 subtopics
- Paper 2
- Paper 2
Monitoring and Controlling Chemical Reactions is examined in Chemistry A Paper 2.
It covers 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.
Sample questions from Monitoring and Controlling Chemical Reactions
Answer each one closed book first, then open the answer.
-
Carrying out an acid–alkali titration
What is meant by the end point of a titration?
Show the answer
It is the point at which the indicator changes colour permanently, showing that the two solutions have just reacted completely. -
Theoretical mass and percentage yield
How is the percentage yield of a reaction calculated?
Show the answer
Divide the actual mass of product obtained by the theoretical mass and multiply by 100. -
Atom economy and its calculation
Under what circumstances does a reaction have an atom economy of 100%?
Show the answer
When there is only one product, so every atom in the reactants ends up in the substance that is wanted. -
Measuring the rate of a reaction, and rate graphs
Give the units in which a rate of reaction is expressed when gas volume is measured, and when mass loss is measured.
Show the answer
Gas volume gives a rate in cm³/s or cm³/min, and mass loss gives a rate in g/s or g/min. -
Factors affecting rate, and collision theory
Which of the factors that change rate applies only to reactions involving gases?
Show the answer
Pressure, because only gases are compressed enough for pressure to change how closely the particles are packed. -
Surface area and rate
A cube of side 3 cm is cut into twenty-seven cubes of side 1 cm. Calculate the new total surface area and the new surface area to volume ratio.
Show the answer
Each small cube has a surface area of 6 cm², so the total is 162 cm² for the same 27 cm³, giving a ratio of 6:1, three times the original. -
Catalysts and how they work
Give two reasons why catalysts are used so widely in industry.
Show the answer
They allow a useful rate at a lower temperature or pressure, which saves energy and money, and they increase the amount of product made per day from the same plant. -
Reversible reactions and dynamic equilibrium
Describe what happens when ammonium chloride is heated and then allowed to cool.
Show the answer
On heating it breaks down into ammonia and hydrogen chloride gases, and on cooling the two gases recombine to form solid ammonium chloride again.
The 9 subtopics
One subtopic is one session. Work down the list.
| Subtopic | What it covers | Questions |
|---|---|---|
| Carrying out an acid–alkali titration | The 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. | 8 |
| Theoretical mass and percentage yield | What 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%. | 17 |
| Atom economy and its calculation | What 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. | 15 |
| Measuring the rate of a reaction, and rate graphs | What 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. | 22 |
| Factors affecting rate, and collision theory | How 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. | 21 |
| Surface area and rate | How 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. | 16 |
| Catalysts and how they work | What 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. | 15 |
| Reversible reactions and dynamic equilibrium | What 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. | 16 |
| Activation energy, and enzymes as catalysts | How 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. | 15 |
How the guide is worked
Answering a question from memory stores it far better than reading the answer again. The guide runs that as a fixed procedure on one subtopic at a time, about twenty minutes a session.
-
Step 1 · Closed book
Cover the answers. Work through one subtopic and write down what you can. Leave blanks where you have nothing.
-
Step 2 · Open book
Go back to the top. Read each printed answer and write it out in full, including the ones you had right.
-
Step 3 · Closed book again
Same questions, same order, from memory. The gap between pass one and pass three is the session result.
Read the full method, the return schedule and the research behind it.
Nearby topics
OCR GCSE Chemistry A, Foundation tier Active Recall Guide
Every topic, not just this one. 1,070 questions with their answers.