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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 8: Measuring the EMF of an Electrochemical Cell (Copper and Zinc Half-Cells)

Aim: To measure the EMF (electromotive force) of an electrochemical cell formed between two metal/metal ion half-cells (e.g., Cu²⁺/Cu and Zn²⁺/Zn) and understand the flow of electrons and standard cell potential.

Method Summary

Electrochemical cell setup with zinc and copper half-cells connected by a salt bridge and voltmeter.

Prepare the Electrodes

  1. Clean zinc and copper strips with emery (sand) paper.
  2. Degrease with cotton wool and propanone.

Prepare the Half-Cells

  1. Place copper strip in 100 cm³ of 1.0 mol dm⁻³ CuSO₄ solution.
  2. Place zinc strip in 100 cm³ of 1.0 mol dm⁻³ ZnSO₄ solution.
  3. Use a salt bridge made of filter paper soaked in saturated KNO₃ solution to connect the two half-cells.

Measure the EMF

  1. Connect the metals to a high-resistance voltmeter using crocodile clips and wires.
  2. Electrons flow from Zn (more reactive, more negative potential) to Cu.
  3. Repeat the process using different concentrations of CuSO₄ and ZnSO₄ solutions to investigate how the Ecell value changes with concentration.

Salt Bridge Explanation

  1. Contains free-moving ions (e.g., K⁺ and NO₃⁻) that maintain charge balance by completing the circuit.
  2. Must not react with solutions.
  3. Can be made by soaking filter paper in a saturated solution of KNO₃.
    4. Salt bridge used in an electrochemical cell, soaked in KNO3 solution to complete the circuit.

Platinum Electrode Use

For redox couples that do not include a metal (e.g., Fe²⁺/Fe³⁺), an inert platinum electrode is used as it conducts electricity without reacting.

Example Reaction & EMF

Half-equations:

Sources of Error