OCR A Level Chemistry B (H433) Past Papers 2026

Fundamentals of Chemistry

Duration: 2h 15m

Scientific Literacy in Chemistry

Duration: 2h 15m

Practical Skills in Chemistry

Duration: 1h 30m

Practical Activity Group

Duration: Throughout the course

Electrode potential reasoning — comparing E° values systematically and applying to corrosion protection or feasibility

Cited as a recurring difficulty in H433/01 2023 (Q34b and Q34d: 'only a small number of candidates scoring any marks at all') and H433/03 2024. Examiners report that answers use 'reactivity' language rather than specific E° comparisons, and that the wrong half-cells are often compared.

H433/01, H433/03

Covalent bond strength — explaining in terms of number of shared electrons attracting both nuclei, not sigma/pi nomenclature

H433/01 2023 Q32(d)(ii): 'a high majority of candidates scored no marks'; misconception box states many answers focused on sigma and pi bonds rather than shared electrons pulling atoms together.

H433/01

Entropy and total entropy change — calculating ΔSsurr from ΔH and T, then combining with ΔSsys for feasibility

H433/01 2024 Q33(e): fewer than half scored all 4 marks; common errors were sign mistakes or calculating only the entropy change of the system without the surroundings. H433/01 2024 series overview lists this as a specific weakness among less successful candidates.

H433/01

Group 2 — solubility trends of hydroxides and sulfates, and charge density explanation using ionic (not atomic) species

H433/01 2023 Q31(c): more than half scored no marks for solubility trends; answers gave 'reactivity' or wrong precipitate colours. H433/01 2024 assessment for learning: 'When considering charge density, it must be ions, not just atoms, or the name of the element.'

H433/01

Sulfonation of benzene and azo dye chemistry — specific reagents, conditions, and mechanisms often forgotten

H433/01 2024 series overview: 'Recall of reagents and conditions for some of the reactions and the content on sulfonation of benzene and azo dyes proved difficult for many candidates.' H433/01 2024 Q35(a): only a minority could name benzenesulfonic acid; even fewer could identify the electrophile.

H433/01

Ion hydration — identifying that hydrating gaseous ions requires breaking H-bonds in water before forming ion-dipole bonds

H433/03 2024 Q4(d)(iii): 'This was amongst the most challenging questions on the paper. Very few candidates realised that to hydrate the (already gaseous) ions requires breaking the H-bonds in water and forming ion-dipole bonds.' Marks were almost exclusively 2 (rare) or 0; common error was citing lattice enthalpy as the endothermic process.

H433/03

Rate determining step in multi-step mechanisms — linking order with respect to each reagent to its presence or absence in the slow step

H433/03 2023 Q4(e): 'Many candidates did not explain the idea of a rate determining step and very few explained that iodine must be in a later fast step.' The 2023 exemplar shows the most common pattern of scoring 2/4 by identifying the step but not explaining why iodine is absent from the rate equation.

H433/01, H433/03

Ionic vs intermolecular bonding — confusing intramolecular lattice energy with intermolecular van der Waals forces, and attributing electrical conduction to delocalised electrons in ionic compounds

H433/03 2024 Q3(c): misconception box identifies two prevalent errors: (1) thinking ionic bonds are stronger than covalent bonds by confusing inter/intramolecular bonding; (2) attributing electrical conductivity of molten ionic compounds to delocalised electrons rather than mobile ions.

H433/03