Mathematical Skills in Chemistry | OCR A-Level Chemistry B (Salters) (H433)
Mathematical Skills in Chemistry
- 121 questions
- 9 subtopics
- Skills strands running through the course
- Component 01, Component 02 and Component 03
The mathematical requirements, assessed across all three components: units and standard form, handling data and significant figures, rearranging and substituting into the standard equations, reading graphs and spectra, and the geometry of molecules..
It covers units, standard form and the mole in calculations, yield, atom economy and logarithmic quantities, significant figures, means and handling data, symbols, and rearranging the standard equations, substituting into rearranged equations, reading spectra and kinetics graphs, gradients, calibration lines and the Arrhenius plot, shapes and bond angles from electron pair repulsion and chiral centres, E/Z isomerism and optical activity.
Sample questions from Mathematical Skills in Chemistry
Answer each one closed book first, then open the answer.
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Units, standard form and the mole in calculations
Express the gas constant 8.314 J mol⁻¹ K⁻¹ in kJ mol⁻¹ K⁻¹.
Show the answer
It is 8.314 × 10⁻³ kJ mol⁻¹ K⁻¹. -
Yield, atom economy and logarithmic quantities
Calculate the percentage by mass of carbon in ethanol, C₂H₅OH, given Mᵣ = 46.0 and Aᵣ(C) = 12.0.
Show the answer
The percentage is (24.0 ÷ 46.0) × 100 = 52.2%. -
Significant figures, means and handling data
Four titres are obtained: 23.90, 22.40, 22.45 and 22.35 cm³. Which is excluded from the mean, and why?
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The 23.90 cm³ value is excluded because it differs from the others by far more than 0.10 cm³ and is therefore an outlier. -
Symbols, and rearranging the standard equations
Rearrange n = cV to make concentration the subject, and then volume.
Show the answer
The rearrangements are c = n/V and V = n/c. -
Substituting into rearranged equations
The enthalpy change of combustion of carbon is −394 kJ mol⁻¹ and of carbon monoxide is −283 kJ mol⁻¹. Calculate the enthalpy change of formation of carbon monoxide.
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Applying Hess's law, ΔHf = −394 − (−283) = −111 kJ mol⁻¹. -
Reading spectra and kinetics graphs
How can the order of a reaction with respect to a species be read from a rate–concentration graph?
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A horizontal line shows zero order, a straight line through the origin shows first order, and an upward curve shows second order. -
Gradients, calibration lines and the Arrhenius plot
An Arrhenius plot has a gradient of −7.20 × 10³ K. What is the activation energy, taking R = 8.314 J mol⁻¹ K⁻¹?
Show the answer
Eₐ = 7.20 × 10³ × 8.314 = 5.99 × 10⁴ J mol⁻¹, which is 59.9 kJ mol⁻¹. -
Shapes and bond angles from electron pair repulsion
State the principle used to predict the shape of a simple molecule.
Show the answer
Electron pairs in the outer shell of the central atom arrange themselves as far apart as possible because they repel one another.
The 9 subtopics
One subtopic is one session. Work down the list.
| Subtopic | What it covers | Questions |
|---|---|---|
| Units, standard form and the mole in calculations | Recall questions on converting volumes and pressures, deducing the units of Kc and of a rate constant, standard form, and mole calculations. | 13 |
| Yield, atom economy and logarithmic quantities | Recall questions on percentage yield and atom economy, why a yield cannot exceed 100%, and converting between pH, [H⁺], Ka and pKa. | 13 |
| Significant figures, means and handling data | Recall questions on counting significant figures, taking the mean of concordant titres, and quoting a result to the precision the data allow. | 22 |
| Symbols, and rearranging the standard equations | Recall questions on what the equilibrium, proportionality and approximation symbols mean, and rearranging n = cV, pV = nRT and q = mcΔT. | 12 |
| Substituting into rearranged equations | Recall questions on working numbers through a rearranged equation for enthalpy, gas volume, Kc, rate and pH. | 13 |
| Reading spectra and kinetics graphs | Recall questions on the axes of a mass spectrum and an infrared spectrum, the integration trace, and reading order from a kinetics graph. | 12 |
| Gradients, calibration lines and the Arrhenius plot | Recall questions on choosing scales, lines of best fit and tangents, calibration lines, and what the gradient and intercept of an Arrhenius plot give. | 12 |
| Shapes and bond angles from electron pair repulsion | Recall questions on the shapes and bond angles of the common molecules and ions, and why lone pairs close the angle. | 14 |
| Chiral centres, E/Z isomerism and optical activity | Recall questions on identifying a chiral centre, the condition for E/Z isomerism, how optical isomers differ, and why a racemic mixture does not rotate light. | 10 |
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.
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Step 1 · Closed book
Cover the answers. Work through one subtopic and write down what you can. Leave blanks where you have nothing.
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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.
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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 A-Level Chemistry B (Salters) Active Recall Guide
Every topic, not just this one. 3,430 questions with their answers.