Students should learn Students should be able to a. Chemical cells in daily life
primary cells and secondary cells
uses of chemical cells in relation to their characteristics such as size, voltage, capacity, rechargeability and price
distinguish between primary and secondary cells
describe the characteristics of common primary and secondary cells:
i. zinc-carbon cell
ii. alkaline manganese cell iii. silver oxide cell
iv. lithium ion cell
v. nickel metal hydride (NiMH) cell vi. lead-acid accumulator
justify uses of different chemical cells for particular purposes
understand the environmental impact of using dry cells
b. Reactions in simple chemical cells
chemical cells consisting of:
i. two metal electrodes and an electrolyte
ii. metal-metal ion half cells and salt bridge/porous device
changes occurring at the electrodes and electron flow in the external circuit
half equations and overall cell equations
describe and demonstrate how to build simple chemical cells using metal electrodes and electrolytes
measure the voltage produced by a chemical cell
explain the problems associated with a simple chemical cell consisting of two metal electrodes and an electrolyte
explain the functions of a salt bridge/porous device
describe and demonstrate how to build simple chemical cells using metal-metal ion half cells and salt bridges/porous devices
explain the differences in voltages produced in chemical cells when different metal couples are used as electrodes
write a half equation representing the reaction at each half cell of a simple chemical cell
write overall equations for simple chemical cells
predict the electron flow in the external circuit and the chemical changes in the simple chemical cells
Students should learn Students should be able to c. Redox reactions
oxidation and reduction
oxidation numbers
common oxidising agents (e.g.
MnO4
(aq)/H+(aq), Cr2O72
(aq)/H+(aq), Fe3+(aq), Cl2(aq), HNO3(aq) of different concentrations and conc. H2SO4(l))
common reducing agents (e.g.
SO32(aq), I(aq), Fe2+(aq), Zn(s))
balancing equations for redox reactions
identify redox reactions, oxidising agents and reducing agents on the basis of
i. gain or loss of oxygen/hydrogen atom(s) ii. gain or loss of electron(s)
iii. changes in oxidation numbers
assign oxidation numbers to the atoms of elements and compounds
construct a general trend of the reducing power of metals and the oxidising power of metal ions
describe the chemical changes of some common oxidising agents and reducing agents
relate the trends of the reducing power and oxidising power of chemical species to their positions in a given electrochemical series
balance half equations of reduction and oxidation
balance redox equations by using half equations or changes in oxidation numbers
d. Redox reactions in chemical cells
chemical cells with inert electrodes
fuel cell
describe and construct chemical cells with inert electrodes
predict the chemical changes at each half cell of the chemical cells with inert electrodes
write a half equation for reaction occurring at each half cell and the overall ionic equation for reaction in the chemical cells with inert electrodes
understand the principles of hydrogen-oxygen fuel cell
write the half equation for reaction occurring at each electrode and the overall equation for reaction in a hydrogen-oxygen fuel cell
state the pros and cons of a hydrogen-oxygen fuel cell
Students should learn Students should be able to e. Electrolysis
electrolysis as the decomposition of substances by electricity as exemplified by electrolysis of i. dilute sulphuric acid
ii. sodium chloride solutions of different concentrations iii. copper(II) sulphate solution
anodic and cathodic reactions
preferential discharge of ions in relation to the electrochemical series, concentration of ions and nature of electrodes
industrial applications of electrolysis in electroplating
describe the materials needed to construct an electrolytic cell
predict products at each electrode of an electrolytic cell with reference to the factors affecting the preferential discharge of ions
describe the anodic and cathodic reactions, overall reaction and observable changes of the electrolyte in electrolytic cells
understand the principles of electroplating
describe the anodic and cathodic reactions, overall reaction and observable changes of electrolyte in electroplating
understand the environmental impact of the electroplating industry
Suggested Learning and Teaching Activities
Students are expected to develop the learning outcomes using a variety of learning experiences. Some related examples are:
making decisions on the choice of chemical cells in daily life based on available information.
making simple chemical cells and measuring their voltages.
writing ionic half equations.
performing experiments to investigate redox reactions with common oxidising and reducing agents.
determining oxidation numbers of atoms in elements and compounds.
balancing redox equations by using ionic half equations or by using oxidation numbers.
investigating redox reactions of concentrated sulphuric acid with metals.
investigating redox reactions of nitric acid of different concentrations with metals.
searching for and presenting information about the applications of fuel cells.
investigating the working principles of a fuel cell car.
performing experiments to investigate the working principles of a lead-acid accumulator.
predicting changes in chemical cells based on given information.
viewing or constructing computer simulations illustrating the reactions in chemical cells.
performing experiments to investigate changes in electrolysis.
performing experiments to study electrolysis of tin(II) chloride solution or dilute sodium chloride solution using microscale apparatus.
performing experiments to investigate factors affecting preferential discharge of ions during electrolysis.
searching for and presenting information about the possible adverse impact of the electroplating industry on the environment.
designing and performing electroplating experiments.
reading articles about the industrial processes involved in the extraction of aluminium from aluminium ore.
discussing the pros and cons of using hydrogen-oxygen fuel cells in vehicles.
investigating the chemistry involved in oxygen absorbers of packaged food.
Values and Attitudes
Students are expected to develop, in particular, the following values and attitudes:
to value the contribution of technological innovations to the quality of life.
to appreciate the usefulness of the concept of oxidation number in the study of redox reactions.
to develop a positive attitude towards the safe handling, storage and disposal of chemicals, and hence adopt safe practices.
to value the need for assessing the impact of technology on our environment.
STSE Connections
Students are encouraged to appreciate and comprehend issues which reflect the interconnections of science, technology, society and the environment. Related examples are:
Various breath-testing technologies, such as passive alcohol sensors, preliminary breath tests, and evidentiary breath tests (e.g. the intoximeter EC/IR) all utilise fuel cell technology to detect alcohol.
Hydrogen-oxygen fuel cells are being used for some areas like space missions and vehicles, but not widely for commercial or domestic purposes.
Lithium cell chemistry variants, such as lithium-ion battery, lithium-ion polymer battery, lithium cobalt battery, lithium manganese battery and lithium nickel battery, have been developed to cope with the need for a wide range of consumer products.
Many electrolytic processes are involved in industrial processes, e.g. refining of metals, the chloroalkali industry and the aluminium production from ore (bauxite).
The development of electrolysis in extracting reactive metals is closely related to human history.