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 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)
- 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
Labels:
Acids,
Bases,
Chemical Bonds,
Electrochemistry,
Form 4,
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Periodic Table,
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SPM Chemistry




