A-Level Chemistry: Year 2 Calculations

Some of the highest-mark questions in A-level Chemistry papers are multi-step calculations from the Year 13 physical and inorganic content. They reward a clear method more than memorised facts: find the moles, apply the right ratio or expression, keep track of units and significant figures. This material gives focused practice on those calculations, with every value you need stated in the question.

The acid–base calculations cover the pH of a buffer made from a weak acid and its salt, the pH of a buffer formed by partly neutralising a weak acid with sodium hydroxide, what happens to a buffer when a little strong acid is added, the pH of a mixture in which the strong base is in excess (using Kw), the pH of a strong acid after dilution and the pH of a strong base.

The equilibrium calculations work from starting moles to equilibrium moles, then to mole fractions and partial pressures, and finally to the value of Kp and its units. The kinetics calculations use the Arrhenius equation in both forms: finding the activation energy from the gradient of a graph of ln k against 1/T (gradient = −Ea/R), and finding how much the rate constant grows for a ten-degree rise. First-order half-life links the rate constant to the time for the concentration to halve.

The redox titration calculations use balanced ionic equations for manganate(VII) and dichromate(VI) with iron(II), ethanedioate and hydrogen peroxide: the concentration of an iron(II) solution, the mass of iron in a tablet, the percentage and formula calculations that follow, and the water of crystallisation in hydrated ammonium iron(II) sulfate.

Three formats are offered. The 12-question quiz gives one calculation per question, with distractors built from the usual slips (a ratio used the wrong way round, a missing factor, a log ratio inverted) and a full worked solution in each explanation. The flashcards collect the relationships you need: the buffer equation, partial pressure, the logarithmic form of the Arrhenius equation, half-life and mole ratios in redox titrations. The written work has eight longer, structured calculations to set out by hand, each with a reference answer showing every step, so you can check both the method and the final value.

The content is based on the A-level chemistry subject content for acids and bases, the equilibrium constant Kp, rate equations and redox titrations, using the approach set out for example in the AQA A-level specification. It is revision practice written by Zestly, not an exam board resource.

• Calculate the pH of acidic buffers, including buffers made by partial neutralisation and after adding a little strong acid
• Calculate pH after mixing a strong acid with excess strong base, after dilution and for a strong base, using Kw
• Calculate Kp and its units from starting and equilibrium moles and the total pressure
• Find an activation energy from a ln k against 1/T graph and use the Arrhenius equation
• Relate the rate constant of a first-order reaction to its half-life
• Carry out redox titration calculations with manganate(VII) and dichromate(VI)

Practice material written by Zestly, based on the A-level chemistry content for acids and bases, Kp, rate equations and redox titrations (for example AQA A-level Chemistry 7405, sections 3.1.9, 3.1.10, 3.1.12 and 3.2.5.5).