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OCR (A) A-Level
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*Revision Materials and Past Papers* 2.1.1 Atomic structure and isotopes 2.1.2 Compounds, formulae and equations 2.1.3 Amount of substance 2.1.4 Acids 2.1.5 Redox 2.2.1 Electron structure 2.2.2 Bonding and structure 3.1.1 Periodicity 3.1.2 Group 2 3.1.3 The halogens 3.1.4 Qualitative analysis 3.2.1 Enthalpy 3.2.2 Reaction Rates 3.2.3 Chemical equilibrium 4.1 Basic concepts and hydrocarbons 4.1.2 Alkanes 4.1.3 Alkenes 4.2.1 Alcohols 4.2.2 Haloalkanes 4.2.3 Organic synthesis 4.2.4 Analytical techniques 5.1.1 How fast? 5.1.2 How far? 5.1.3 Acids, bases and buffers 5.2.1 Lattice enthalpy 5.2.2 Enthalpy and entropy 5.2.3 Redox and electrode potentials 5.3.1 Transition elements 5.3.2 Qualitative analysis 6.1.1 Aromatic compounds 6.1.2 Carbonyl compounds 6.1.3 Carboxylic acids and esters 6.2.1 Amines 6.2.2 Amino acids, amides and chirality 6.2.3 Polyesters and polyamides 6.2.4 Carbon–carbon bond formation 6.2.5 Organic synthesis 6.3.1 Chromatography and qualitative analysis 6.3.2 Spectroscopy Required Practicals

Required Practicals

1 Moles determination 2 Acid–base titration 3 Enthalpy determination 4 Qualitative analysis of ions 5 Synthesis of an organic liquid 6 Synthesis of an organic solid 7 Qualitative analysis of organic functional groups 8 Electrochemical cells 9 Rates of reaction – continuous monitoring method 10 Rates of reaction – initial rates method 11 pH measurement 12 Research skills

Core Practical 1: Moles Determination

Aim: To determine the percentage purity of an impure sample of copper(II) carbonate by measuring the volume of CO₂ gas produced when it reacts with excess sulfuric acid.

Chemical Reaction

Reaction equation:
CuCO3(s) + H2SO4(aq) → CuSO4(aq) + H2O(l) + CO2(g)

From the equation, 1 mole of CuCO3 produces 1 mole of CO2.

Note from Matt – you may have carried out a different practical to the example here. That is fine, don’t worry – the key thing is that you know how to accurately measure masses of solids and volumes of gases, using these measurements to determine moles.

Safety Notes

Apparatus and Chemicals

Equipment

Chemicals

Method

OCR (A) A-Level Chemistry practical setup showing CuCO3 reacting with H2SO4 and CO2 collected in an inverted measuring cylinder.
  1. Weigh a sample of impure copper(II) carbonate (e.g. 1.50 g).
  2. Add 50 cm³ of 1.0 mol dm⁻³ sulfuric acid to a conical flask connected via a delivery tube to a filled, inverted measuring cylinder in a trough of water (or to a gas syringe).
  3. Quickly add the copper(II) carbonate and seal the flask with a bung.
  4. Measure the volume of CO₂ collected until no more gas is produced.
  5. Record the volume of gas collected, along with room temperature and pressure.

Example Calculations

Measurements:

  1. Convert volume of gas to m³:
    168 cm³ = 0.000168 m³
  2. Use Ideal Gas Equation:
    PV = nRT → n = PV ÷ RT
    n = (100,000 × 0.000168) ÷ (8.31 × 298)
    n ≈ 6.78 × 10⁻³ mol of CO₂
    This is also the number of moles of pure CuCO₃.
  3. Calculate the mass of pure CuCO₃:
    Mr of CuCO₃ = 63.5 + 12.0 + (3 × 16.0) = 123.5 g mol⁻¹
    Mass = moles × Mr = 6.78 × 10⁻³ × 123.5 ≈ 0.838 g
  4. Calculate percentage purity:
    Purity = (mass of pure CuCO₃ ÷ total mass of sample) × 100
    Purity = (0.838 ÷ 1.50) × 100 ≈ 55.9%

Potential Sources of Error

Improvements