OCR A-Level Chemistry B (Salters) sample questions and answers (H433)
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64 sample questions and answers
Taken from every topic of OCR A-Level Chemistry B (Salters), specification H433. The full guide has 3,430.
Component 01, Component 02, Component 03
Development of Practical Skills in Chemistry
166 questions in the guide, across 12 subtopics. More from this topic
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Planning experiments
Why is a gas syringe usually a better choice than collecting a gas over water?
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A gas syringe measures the full volume produced even for gases that dissolve in water, such as carbon dioxide or ammonia, whereas collection over water loses some of the gas to solution. -
Implementing: apparatus, units and recording data
How should the columns of a results table be headed?
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Each heading gives the quantity and its unit, separated by a solidus, for example volume of acid / cm³. -
Graphs, gradients and drawing a conclusion
What determines the unit of a gradient?
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The gradient takes the unit of the vertical axis divided by the unit of the horizontal axis. -
Anomalous results, precision, accuracy and types of error
Which type of error is reduced by repeating a measurement and averaging?
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Only random error is reduced, because positive and negative deviations tend to cancel; a systematic error remains unchanged. -
Hazards, risk and control measures
Why is concentrated sulfuric acid always added to water rather than water to acid?
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Dilution is strongly exothermic, and adding water to the acid releases the heat in a small volume, which can boil and spit corrosive liquid out of the vessel.
Component 01, Component 02, Component 03
Elements of Life
267 questions in the guide, across 18 subtopics. More from this topic
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The mole, relative masses and empirical formulae
Define relative atomic mass.
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It is the weighted mean mass of an atom of an element, taking account of the abundance of each isotope, compared with one twelfth of the mass of one atom of carbon-12. -
Orbitals, sub-shells and electron configurations
Why do electrons occupy the three p-orbitals singly before any of them pairs up?
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Electrons repel one another, so they stay in separate orbitals for as long as possible to keep as far apart as they can. -
Fusion reactions and the origin of the elements
What particle is represented by the symbol ⁰₊₁e?
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It is a positron, a particle with the same mass as an electron but a charge of +1. -
Melting point, conductivity and solubility of each structure
When solid iodine turns to vapour, what is being broken?
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Only the weak attractions between the I₂ molecules are broken; the covalent bonds inside each molecule stay intact. -
The periodic table, the blocks and trends in melting point
Which groups make up the s-block and which make up the p-block?
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The s-block is Groups 1 and 2, and the p-block runs from Group 3 to Group 0.
Component 01, Component 02, Component 03
Developing Fuels
364 questions in the guide, across 24 subtopics. More from this topic
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Molar gas volume and the ideal gas equation
What amount of gas, in moles, is present in 720 cm³ of oxygen at RTP?
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720 cm³ is 0.720 dm³, so the amount is 0.720 ÷ 24.0 = 0.0300 mol. -
Enthalpy changes: definitions and standard conditions
Why is an enthalpy change of combustion always negative?
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Burning always releases energy to the surroundings, so the value can never be positive. -
Burning a fuel, correcting for heat loss, and the assumptions made
Apart from heat loss, give a source of error when burning a volatile fuel.
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Some of the fuel evaporates without burning, so the loss in mass overstates the amount actually burned. -
Cracking and how it is carried out
Write an equation for the cracking of decane into octane and one other product.
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C₁₀H₂₂ → C₈H₁₈ + C₂H₄. -
Aliphatic and aromatic compounds, functional groups and general formulae
Give the molecular formula of benzene.
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Benzene is C₆H₆.
Component 01, Component 02, Component 03
Elements from the Sea
357 questions in the guide, across 22 subtopics. More from this topic
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Atom economy
In the Deacon reaction the only substance formed alongside chlorine is water. Why does this soften the impact of the atom economy being below 100%?
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The mass that does not become chlorine leaves as water, which is harmless, so little is genuinely wasted. -
Electrolysis of molten salts and writing electrode half-equations
Write the anode half-equation for the electrolysis of molten aluminium oxide.
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2O²⁻ → O₂ + 4e⁻. -
The rules for assigning oxidation states
What is the usual oxidation state of hydrogen in its compounds, and when does it differ?
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It is +1, except in metal hydrides such as NaH, where it is −1. -
Balancing a redox equation with oxidation states
Write the equation for iodine reacting with thiosulfate ions.
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I₂ + 2S₂O₃²⁻ → 2I⁻ + S₄O₆²⁻. -
Physical properties of the halogens
Describe the trend in boiling point down Group 7.
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Boiling point rises steadily from fluorine through to iodine.
Component 01, Component 02, Component 03
The Ozone Story
355 questions in the guide, across 21 subtopics. More from this topic
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Electronegativity and bond polarity
What does the label δ+ on an atom mean?
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It means the atom carries a small partial positive charge because the bonding electrons have been drawn away from it. -
Boiling points and intermolecular bonds
Butane and propanone both have Mr 58.0, so why does butane boil at −0.5 °C and propanone at 56 °C?
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With the same Mr their instantaneous dipole–induced dipole bonds are similar, but propanone is polar and so has additional permanent dipole–permanent dipole attractions that need more energy to overcome. -
Following a reaction and finding the rate from a graph
Why must a kinetics experiment be carried out in a thermostatted water bath?
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Rate is extremely sensitive to temperature, so the temperature must be held constant if the effect of the variable actually being changed is to be seen. -
Homogeneous catalysis and intermediates
Roughly how many ozone molecules can a single chlorine radical destroy?
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Of the order of 10⁵ ozone molecules, before the radical is finally removed from the cycle. -
Primary, secondary and tertiary haloalkanes, and the amines
Name the functional group of a primary amine and give its formula.
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It is the amino group, –NH₂.
Component 01, Component 02, Component 03
What's in a Medicine?
235 questions in the guide, across 17 subtopics. More from this topic
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Formulae of oxygen-containing homologous series
Give the molecular formula of ethanoic anhydride.
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Ethanoic anhydride is (CH₃CO)₂O, molecular formula C₄H₆O₃. -
The acidity of phenol compared with alcohols and carboxylic acids
What is the name of the salt formed when phenol reacts with sodium hydroxide?
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Sodium phenoxide is formed. -
Esterification and oxidising primary, secondary and tertiary alcohols
State the oxidising mixture used to oxidise alcohols.
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Potassium dichromate(VI) solution acidified with dilute sulfuric acid is used. -
Preparing aspirin, filtering under reduced pressure and recrystallisation
Give two advantages of filtration under reduced pressure over gravity filtration.
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It is much faster, and it leaves the solid drier because air is pulled through the crystals. -
Reflux and distillation in an organic preparation
Why are anti-bumping granules added before refluxing?
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They provide nucleation sites for small, steady bubbles and so prevent violent, uneven boiling.
Component 01, Component 02, Component 03
The Chemical Industry
250 questions in the guide, across 16 subtopics. More from this topic
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Rate equations, order and the rate constant
Can the orders in a rate equation be predicted from the balanced equation?
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No, orders can only be found by experiment, because they depend on the mechanism rather than on the overall stoichiometry. -
Half-lives
Rearrange that relationship to give k in terms of the half-life.
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k = ln2 ÷ t½. -
Reading order from concentration-time and rate-concentration graphs
What shape of concentration–time graph indicates a zero-order reaction?
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A straight line of constant negative gradient until the reactant runs out. -
The ln k against 1/T plot and finding the activation enthalpy
An Arrhenius plot has a gradient of −6.50 × 10³ K. Calculate the activation enthalpy in kJ mol⁻¹.
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Ea = 6.50 × 10³ × 8.314 = 5.40 × 10⁴ J mol⁻¹, which is 54.0 kJ mol⁻¹. -
Effect of conditions on the magnitude of the equilibrium constant
What effect does a change of pressure have on the magnitude of Kc?
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None; Kc is unchanged by pressure.
Component 01, Component 02, Component 03
Polymers and Life
376 questions in the guide, across 21 subtopics. More from this topic
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Amino acids, the peptide link and hydrolysing a protein
Which two functional groups react when a peptide link forms, and what is eliminated?
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The COOH of one amino acid reacts with the NH₂ of another, and a molecule of water is eliminated. -
Protein structure
What happens to a protein when it is denatured?
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The hydrogen bonds and ionic attractions holding its tertiary structure break, so the chain unfolds and loses its specific shape and function. -
Molecular recognition
Why must the bonds holding a drug to a receptor usually be weak?
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The drug has to be released again once it has acted, which would be impossible if it were bound covalently. -
Characteristics of enzyme catalysis
Why do many medicines work as enzyme inhibitors?
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Blocking a specific enzyme in a pathway shuts down the process that depends on it, and the specificity of the active site means other enzymes are unaffected. -
Basicity of amines
Write an equation for the reaction of ethylamine with hydrochloric acid.
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CH₃CH₂NH₂ + HCl → CH₃CH₂NH₃⁺Cl⁻.
Component 01, Component 02, Component 03
Oceans
282 questions in the guide, across 19 subtopics. More from this topic
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Solubility in aqueous and non-aqueous solvents
What does the rule 'like dissolves like' mean in terms of intermolecular bonds?
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A solute dissolves readily when the solute–solvent bonds formed are of a similar type and strength to the solute–solute and solvent–solvent bonds that have to be broken. -
Measuring an enthalpy change of solution
What assumption is made about the mass used in q = mcΔT for an experiment on dissolving?
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The mass of water is taken as the mass of the whole solution, and the solution is assumed to have the same specific heat capacity as water. -
Entropy: qualitative treatment
Predict the sign of ΔsysS for N₂(g) + 3H₂(g) ⇌ 2NH₃(g).
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It is negative, because four moles of gas become two moles of gas. -
The limiting temperature, and why a feasible reaction may not happen
A reaction has a positive ΔH and a negative ΔsysS. What can you say about its feasibility?
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It is not feasible at any temperature, because both contributions to ΔtotS are negative. -
The solubility product expression, its units and calculations
What are the units of Ksp for silver chloride?
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They are mol² dm⁻⁶.
Component 01, Component 02, Component 03
Developing Metals
304 questions in the guide, across 18 subtopics. More from this topic
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Manganate(VII) titrations and their calculations
Which acid is used to acidify a manganate(VII) titration, and why is hydrochloric acid avoided?
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Dilute sulfuric acid is used, because manganate(VII) would oxidise the chloride ions of hydrochloric acid and the titre would be too large. -
Shapes of complexes and coordination number
What are the bond angles in an octahedral complex?
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Every neighbouring pair of ligands is separated by 90°, and each ligand is 180° from the one directly opposite it through the metal. -
Simple electrochemical cells
What temperature and pressure are used as standard for electrode potential measurements?
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The temperature is 298 K and the pressure is 100 kPa. -
Standard electrode potentials and calculating E°cell
What does a strongly negative standard electrode potential tell you about the species involved?
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The reduced form releases electrons readily, so it is a good reducing agent, while the oxidised form is a poor oxidising agent. -
Transition metals: definition, oxidation states and colours
What is the colour of an aqueous iron(III) solution?
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The hexaaqua ion is pale violet, although in practice such solutions usually look yellow-brown.
Component 01, Component 02, Component 03
Colour by Design
312 questions in the guide, across 20 subtopics. More from this topic
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How dyes attach to fibres
Describe how an acid dye bonds to wool.
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The dye's negatively charged sulfonate groups form ionic bonds with positively charged –NH₃⁺ groups on the protein chains of the wool. -
Fats and oils
Why does bromine water lose its colour with an unsaturated oil?
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Bromine adds across the carbon–carbon double bonds, so the coloured bromine is used up. -
Tests for the common functional groups
How can a carboxylic acid be distinguished from a phenol in a test tube?
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Add sodium carbonate solution; the carboxylic acid effervesces as carbon dioxide is released, while the phenol does not react. -
Halogenation and nitration of benzene and the electrophiles involved
Name the products of the nitration of benzene.
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Nitrobenzene, C₆H₅NO₂, together with water. -
Coupling reactions, azo dyes and the route from benzene
Explain why azo dyes are so intensely coloured.
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The delocalisation runs across both rings and the azo group, so the gap between electronic energy levels is small and visible light is absorbed strongly.
Component 01, Component 02, Component 03
Chemical Literacy
41 questions in the guide, across 2 subtopics. More from this topic
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Extracting and using data and information from a scientific text
A text describes haematite as Fe₂O₃. Calculate the percentage by mass of iron in it, given Aᵣ(Fe) = 55.8 and Aᵣ(O) = 16.0.
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Mᵣ(Fe₂O₃) = 159.6, so the percentage of iron is (111.6 ÷ 159.6) × 100 = 69.9%. -
Extracting and using data and information from a scientific text
Why should an answer based on an article be quoted to no more significant figures than the article's data?
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The calculated result cannot be more precise than the least precise value it was derived from. -
Written communication and comprehension
What is the difference between saying a reaction is energetically feasible and saying it is fast?
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Feasibility is a thermodynamic statement that ΔtotS is positive, while speed is a kinetic matter governed by activation enthalpy; a feasible reaction can still be immeasurably slow. -
Written communication and comprehension
Why is "it goes cloudy" a weaker observation than "a white precipitate forms"?
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The second identifies both the physical change and the colour of the solid formed, which is the evidence needed to identify the ion present.
Component 01, Component 02, Component 03
Mathematical Skills in Chemistry
121 questions in the guide, across 9 subtopics. More from this topic
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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.
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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.
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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.
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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.
OCR A-Level Chemistry B (Salters) Active Recall Guide
The other 3,366 questions, with the answers printed after each section.