What is electrolysis?

electrolysis
Electrolysis is the production of a chemical reaction by passing an electric current through an electrolyte. In electrolysis, positive ions transfer to the cathode and negative ions to the anode. The reactions occurring depend on electron transfer at the electrodes and are therefore redox reactions. At the anode, negative ions in solution may lose electrons to form neutral species. Alternatively, atoms of the electrode can lose electrons and go into solution as positive ions. In either case the reaction is an oxidation. At the cathode, positive ions in solution can gain electrons to form neutral species. Thus cathode reactions are reductions.

What is electrolyte?

electrolyte
Electrolyte is a liquid that conducts electricity as a result of the presence of positive or negative ions. Electrolytes are molten ionic compounds or solutions containing ions, i.e. solutions of ionic salts or of compounds that ionize in solution. Liquid metals, in which the conduction is by free electrons, are not usually regarded as electrolytes. Solid conductors of ions, as in the sodium–sulphur cell, are also known as electrolytes.

e.g. acids, alkali, salts dissolved in water, molten salts

Electrolysis of molten lead (II) bromide

During the electrolysis of molten lead(II) bromide, PbBr2, bromine gas, Br2 is released at the cathode while the lead metal is formed at the anode.  

Pb2+ and Br- ions are present in the molten lead(II) bromide, PbBr2.  At the anode, bromide ions, Br- are discharged by donating electrons to form bromine molecules, Br2. At the cathode, each lead(II) ion, Pb2+ is discharged by accepting two electrons to form a lead atom.

SPM Form 4: Electrochemistry (Checklist)

electrochemistry
  • Electrode: A conductor in the form of a wire, rod or plate which carry electric current in and out of an electrolyte during electrolysis.
  • Electrolyte: A substances that can conduct electricity in molten state or aqueous solution and is decomposed by electric current.
  • Non-electrolyte: A substances that cannot conduct electricity in molten state or aqueous solution.
  • Anion: A negatively-charged ion.
  • Cation: A positively-charged ion.
  • Anode: An electrode which is connected to the positive terminal of the source of electricity during electrolysis. (donation of electrons)
  • Cathode: An electrode which is connected to the negative terminal of the source of electricity during electrolysis. (acceptance of electrons)
  • Electrolysis: The process whereby a compound is broken down into its constituent elements when electricity is passed through an electrolyte.
  • Aqueous solution: A solution produced when a compound is dissolved in water.
  • Electrochemical series: An arrangement of metals based on the tendency of each metal to donate electrons.
  • The lower the position of an ion in the electrochemical series, the higher is the tendency of the ions to be discharged.
  • Purification of metals: The process of obtaining a pure metal from an impure metal through electrolysis. E.g. Impure copper can be purified through electrolysis when the impure copper is used as the anode and a pure copper is used as the cathode.
  • Electroplating of metals: The process of coating a layer of metal onto another metal using electrolysis.
  • Simple voltaic acid: A cell that converts chemical energy to electrical energy. The chemical reactions in a simple voltaic cell produce electricity. No current flow will flow if both electrodes are made of the same metal.
  • Electropositivity: A measurement of the ability of an atom to donate electrons to form a positive ion.
  • Displacement reaction: A reaction where a more electropositive metal displace another metal from its salt solution. A metal which has a higher position in the electrochemical series is able to displace the metal below it in the series from their salt solutions.


STPM Chemistry Syllabus 2nd Term

Chapter 7: Chemical Energetics
7.1 Enthalpy changes of reaction, ΔH
7.2 Hess’ law
7.3 Born-Haber cycle
7.4 The solubility of solids in liquids

Chapter 8: Electrochemistry
8.1 Half-cell and redox equations
8.2 Standard electrode potential
8.3 Non-standard cell potentials
8.4 Fuel cells
8.5 Electrolysis
8.6 Applications of electrochemistry

Chapter 9: Periodic Table: Periodicity
9.1 Physical properties of elements of Period 2 and Period 3
9.2 Reactions of Period 3 elements with oxygen and water
9.3 Acidic and basic properties of oxides and hydrolysis of oxides

Chapter 10: Group 2
10.1 Selected Group 2 elements and their compounds
10.2 Anomalous behavior of beryllium
10.3 Uses of Group 2

Chapter 11: Group 14
11.1 Physical properties of Group 14 elements
11.2 Tetrachlorides and oxides of Group 14 elements
11.3 Relative stability of +2 and +4 oxidation states of Group 14 elements
11.4 Silicon, silicone and silicates
11.5 Tin alloys

Chapter 12: Group 17
12.1 Physical properties of selected Group 17 elements
12.2 Reactions of selected Group 17 elements
12.3 Reactions of selected halide ions
12.4 Industrial applications of halogens and their compounds

Chapter 13: Transition elements
13.1 Physical properties of first row transition elements
13.2 Chemical properties of first row transition elements
13.3 Nomenclature and bonding of complexes
13.4 Uses of first row transition elements and their compounds

SPM Chemistry Syllabus Form 4

Chapter 1: Introduction to Chemistry
1.1 Chemistry and its importance
1:2 Scientific methods

Chapter 2: The Structure of the Atom
2.1 Matter
2.2 The atomic structure
2.3 Isotopes
2.4 The electronic structure of an atom

Chapter 3: Chemical Formulae and Equations
3.1 Relative atomic mass and relative molecular mass
3.2 The mole and the number of particles
3.3 The mole and the mass of substances
3.4 The mole and the volume of gas
3.5 Chemical Formulae
3.6 Chemical Equations

Chapter 4: Periodic Table of Elements
4.1 The Periodic Table of Elements
4.2 Group 18 elements
4.3 Group 1 elements
4.4 Group 17 elements
4.5 Elements in a period
4.6 Transition elements

Chapter 5: Chemical Bonds
5.1 Formation of compounds
5.2 Ionic bonds
5.3 Covalent bonds
5.4 The properties of ionic and covalent compounds

Chapter 6: Electrochemistry
6.1 Electrolytes and non-electrolytes
6.2 Electrolysis of molten compounds
6.3 Electrolysis of aqueous solutions
6.4 Electrolysis in industries
6.5 Voltaic cells
6.6 The electrochemical series

Chapter 7: Acids and bases
7.1 Acids and bases
7.2 The strength of acids and alkalis
7.3 Concentrations of acids and alkalis
7.4 Neutralization

Chapter 8: Salts
8.1 Salts
8.2 Qualitative analysis of salts

Chapter 9: Manufactured Substances in Industry
9.1 Sulphuric acid
9.2 Ammonia and its salts
9.3 Alloys
9.4 Synthetic polymers
9.5 Glass and polymers
9.6 Composite materials