The data section, explained | A Level Chemistry 9701

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The 9701 syllabus ends with a data section: nine tables of constants and chemical data that the examinations draw on. This page is a guide to it — what each table contains, which topics use it, how to read it, and the traps in each. It is not a copy of Cambridge’s data section. Download the syllabus for your examination year and use the tables in it (or the values printed in your paper) as the ones that count.

📚Why it matters

Knowing what you are given changes how you revise. You do not need to memorise the gas constant, the Avogadro constant, bond energies, ionisation energies, electronegativities, electrode potentials, NMR shifts or IR ranges — but you do need to know how to use each table quickly and correctly, and you need to know what is not there, because that you must learn. Values a question relies on are either printed in the paper or quoted in the question itself; the syllabus says, for example, that Pauling electronegativity values “will be given where necessary”. Look at a recent past paper to see exactly how your papers present them.

📏1. Important values, constants and standards

molar gas constant R = 8.31 J K⁻¹ mol⁻¹

Faraday constant F = 9.65 × 10⁴ C mol⁻¹

Avogadro constant L = 6.022 × 10²³ mol⁻¹

electronic charge e = −1.60 × 10⁻¹⁹ C

molar volume 22.4 dm³ mol⁻¹ at s.t.p. (101 kPa, 273 K)

molar volume 24.0 dm³ mol⁻¹ at room conditions

ionic product of water K_w = 1.00 × 10⁻¹⁴ mol² dm⁻⁶ at 298 K

specific heat capacity of water c = 4.18 J g⁻¹ K⁻¹ (4.18 kJ kg⁻¹ K⁻¹)

Used in: moles and gas volumes (topic 2), pV = nRT (topic 4), calorimetry (topic 5), electrolysis and the Nernst equation (topic 24), pH and K_w (topic 25).
Trap: the two molar volumes. Use 24.0 for “room temperature and pressure” and 22.4 only if a question says s.t.p. For any other conditions, use pV = nRT.
Trap: R is in J, so pV = nRT needs Pa and m³. c is per gram, so q = mcΔT gives J when m is in g.
F = L × e (the charge on one mole of electrons): 6.022 × 10²³ × 1.60 × 10⁻¹⁹ = 9.64 × 10⁴. That relationship is examined at A Level, as a way of determining the Avogadro constant by electrolysis.

⚡2. Ionisation energies

The first four ionisation energies, in kJ mol⁻¹, of hydrogen to krypton and a selection of heavier elements.

Used in: trends and anomalies across periods and down groups, and deducing an element’s group from successive values (topic 1); periodicity (topic 9); Born–Haber cycles (topic 23).
How to read it: for successive values, look for the biggest ratio between neighbours, not the biggest number — every successive value is bigger than the last.
Trap: in a Born–Haber cycle for a 2+ ion you need the sum of the first and second ionisation energies, both from the table.

🔗3. Bond energies

Two lists: diatomic molecules, where the values are exact (H–H, the halogens, the hydrogen halides, N≡N, O=O, C≡O), and polyatomic molecules, where they are averages (C–H, C–C, C=C, C–O, O–H and so on).

Used in: estimating ΔH from bonds broken and made (topic 5); bond strength and reactivity, such as N≡N and the hydrogen halides (topic 3, topic 11); C–X bond strength and halogenoalkane reactivity (topic 15).
Special values: C=O has a general value and a separate, larger one for C=O in CO₂ (805). Silicon–oxygen bonds differ between solid SiO₂ and gaseous SiO₂. Use the specific value when the question involves that molecule.
Trap: bond energies are for the gaseous state. A ΔH from bond energies ignores condensation of water and other liquids, and uses averages, so it will not match a measured value exactly — and questions often ask you to explain why.

🔋4. Standard electrode potentials

Standard reduction potentials, E^⦵ at 298 K, each written as a reduction half-equation, for example Cu²⁺ + 2e⁻ ⇌ Cu, +0.34 V.

Used in: cell e.m.f., predicting the feasibility of redox reactions, and the chemistry of the transition elements (A Level topics 24 and 28).
How to read it: the list is in alphabetical order of the element, not in order of E^⦵. Find the two half-equations you need yourself. The more positive the value, the more readily the species on the left is reduced — the stronger an oxidising agent it is.
Trap: several elements appear more than once (Fe³⁺/Fe²⁺, Fe²⁺/Fe and Fe³⁺/Fe; the various chromium, copper and manganese couples). Match the exact species in the question, including any H⁺, OH⁻ or ligands.
Trap: never multiply E^⦵ by the number of electrons when you balance the equation. The potential does not depend on how many moles react.

🧲5. Pauling electronegativity values

Values for the lighter elements, from H to Br. Worth knowing are the scale’s key figures as this syllabus prints them: H 2.1, C 2.5, N 3.0, O 3.5, F 4.0, Cl 3.0, Na 0.9.

Used in: bond polarity and predicting ionic or covalent bonding (topic 3); the change from ionic to covalent oxides and chlorides across period 3 (topic 9).
Trap: other textbooks and websites use slightly different values (Cl 3.2, H 2.2). In an exam, use the values printed in the paper.

🧬6 and 7. NMR chemical shifts

Typical chemical shift ranges, δ in ppm relative to TMS = 0, for ¹H (protons) and ¹³C, each grouped by the environment of the atom — for protons, for example, alkyl, next to C=O, next to an electronegative atom, on an alkene, on an aromatic ring, in an aldehyde, and in OH and NH groups.

Used in: A Level topic 37 only.
How to read it: the ranges overlap, so a shift rarely identifies an environment on its own. Combine it with the number of peaks, the integration (for ¹H) and the splitting pattern.
Trap: the table notes that O–H and N–H shifts vary with solvent and concentration, so their ranges are wide. Confirm them by exchange with D₂O (the peak disappears) rather than by position.

🌈8. Infrared absorptions

Characteristic absorption ranges, in wavenumbers (cm⁻¹), for C–O, C=C, C=O (amide, carbonyl and carboxyl, ester), C≡N, C–H, N–H and O–H (carboxyl and hydroxy). The full list, with how to use it, is on the topic 22 page.

Used in: identifying functional groups (topic 22), and at A Level alongside NMR (topic 37).
Version note: the hydroxy O–H range is printed as 3200–3600 cm⁻¹ in the 2025–2027 syllabus and 3200–3650 in the 2028–2030 one. The difference will not change an answer, but quote the range from your own paper.
Trap: the carboxyl O–H is a separate, lower, very broad range (2500–3000). Spotting which O–H you have is how you tell an acid from an alcohol.

🔮9. The Periodic Table

Element names, symbols, atomic numbers and relative atomic masses.

Used in: every calculation. Take A_r values from the table given, to the precision given: Cl is 35.5, Cu 63.5, Mg 24.3 — not the rounded whole numbers from earlier courses.
Trap: the 2028–2030 table changes one value (neodymium, 144.2 instead of 144.4). Nothing in this syllabus depends on neodymium, but it is a reminder that the paper in front of you is the authority.

🚫What is not in the data section

This is the part to learn. The data section contains no equations, and no values for many quantities you will use:

Equations: n = m/M, c = n/V, pV = nRT, q = mcΔT, ΔG = ΔH − TΔS, pH = −log[H⁺], K_a and K_sp expressions, the half-life relationship, Q = It, the Nernst equation, and the [M+1]⁺ carbon-counting formula. Learn them all; do not rely on any being printed.
Definitions: every enthalpy change, electronegativity, ionisation energy, standard electrode potential — these are recall.
Values given only in questions: enthalpy changes of formation and combustion, lattice energies, K_a, K_sp, indicator ranges and stability constants are never in the data section. If a calculation needs one, the question supplies it.
Qualitative analysis: the tests for cations, anions, gases and elements are in a separate set of qualitative analysis notes printed in the Paper 3 exam paper, not in the data section. Know them well enough to use them quickly.

✏️Worked example

Using only values from the data section, estimate the enthalpy change for H₂(g) + Cl₂(g) → 2HCl(g), and state whether your answer is exact or an estimate.

All three molecules are diatomic, so the data section gives exact values: H–H 436, Cl–Cl 242, H–Cl 431 kJ mol⁻¹.

\[ \Delta H = (436 + 242) - 2(431) = 678 - 862 = -184\ \mathrm{kJ\ mol^{-1}} \]

Because every bond energy here is exact, not an average, and every species is a gas, this is the actual enthalpy change for the reaction as written, not an estimate — unlike the methane and ethanol combustion estimates in topic 5.

Check it. The accepted ΔH_f of HCl(g) is about −92 kJ mol⁻¹, and this equation forms two moles: 2 × (−92) = −184. The data-section answer matches exactly, which is the point of exact bond energies.

Calling every bond-energy answer “approximate”. Only average bond energies, or non-gaseous species, make the answer approximate. Knowing which list a value comes from — exact diatomic or average polyatomic — is exactly what the syllabus asks when it says you should understand that some bond energies are exact and some are averages.

📝Practise

Work through these, then reveal the answer. Each question is about using a different table.

1. Which molar volume would you use for 0.0500 mol of gas at 20 °C and 101 kPa, and what volume does it occupy?

20 °C and 101 kPa are room conditions, so use 24.0 dm³ mol⁻¹: V = 0.0500 × 24.0 = 1.20 dm³. The 22.4 value is for 273 K (0 °C) only.

2. Use F and L to calculate the charge on one electron.

F is the charge on one mole of electrons, so e = F / L = 9.65 × 10⁴ / 6.022 × 10²³ = 1.60 × 10⁻¹⁹ C, which matches the value of e given in the same table.

3. Why does the data section give a separate bond energy for C=O in CO₂?

Most C=O values are averages over many compounds (aldehydes, ketones, acids), in which the bond energy varies with what else is attached. The C=O bond in carbon dioxide is noticeably stronger (805 against about 740 kJ mol⁻¹), and CO₂ appears in every combustion calculation, so using the general value would put a large, systematic error into every combustion estimate.

4. A student looks for “the strongest oxidising agent” in the E^⦵ table by reading the first entry. What is wrong with this?

The table is in alphabetical order, not in order of potential, so the first entry has nothing to do with oxidising power. The strongest oxidising agent is the species on the left of the half-equation with the most positive E^⦵ — which has to be found by scanning the whole list (it is F₂, +2.87 V).

5. An IR spectrum shows a very broad absorption at 2500–3000 cm⁻¹ and a strong one at 1710. Which bonds, and which functional group?

2500–3000 (very broad) is O–H in a carboxyl group; 1710 is C=O. Together: a carboxylic acid. An alcohol’s O–H would be at 3200–3600 and there would be no C=O.

6. Name three quantities you need in 9701 calculations that are not in the data section, and say where each comes from.

Any three, for example: enthalpy changes of formation or combustion — given in the question; K_a or K_sp — given in the question; indicator colour-change ranges — given in the question; equations such as pV = nRT, q = mcΔT or pH = −log[H⁺] — never given, so they must be learned.

🎓The official source

This page is a guide, not a substitute.

The 9701 syllabus for your examination years — the data section is at the back. Print it and keep it with your notes, so that you revise with the same tables the papers use.
Recent past papers — to see which values are printed in each paper and how data are supplied inside questions.