Overview
Metals have a wide range of uses in daily life. Therefore, the extraction of metals from their ores has been an important activity of human beings since prehistoric times. This topic provides opportunities for students to develop an understanding of how metals are extracted from their ores and how they react with other substances. Students are expected to establish a reactivity series of metals based on experimental evidence.
The corrosion of metals poses a socioeconomic problem to human beings. It is therefore necessary to develop methods to preserve the limited reserve of metals. An investigation of factors leading to corrosion and of methods to prevent metals from corroding is a valuable problem-solving exercise and can help students develop a positive attitude towards the use of resources on our planet.
A chemical equation is a concise and universally adopted way to represent a chemical reaction. Students should be able to transcribe word equations into chemical equations and appreciate that a chemical equation shows a quantitative relationship between reactants and products in a reaction. Students should also be able to perform calculations involving the mole and chemical equations. The mole concepts acquired from this topic prepare students for performing further calculations involving concentration of solutions, molar volume of gases and equilibrium constant of reaction in other topics of the curriculum.
Students should learn Students should be able to a. Occurrence and extraction of metals
occurrence of metals in nature in free state and in combined forms
obtaining metals by heating metal oxides or by heating metal oxides with carbon
extraction of metals by electrolysis
relation of the discovery of metals with the ease of extraction of metals and the availability of raw materials
limited reserves of metals and their
state the sources of metals and their occurrence in nature
explain why extraction of metals is needed
understand that the extraction of metals involves reduction of their ores
describe and explain the major methods of extraction of metals from their ores
relate the ease of obtaining metals from their ores to the reactivity of the metals
deduce the order of discovery of some metals from their relative ease of extraction
Students should learn Students should be able to
describe metal ores as a finite resource and hence the need to recycle metals
evaluate the recycling of metals from social, economic and environmental perspectives b. Reactivity of metals
reactions of some common metals (sodium, calcium, magnesium, zinc, iron, lead, copper, etc.) with oxygen/air, water, dilute
hydrochloric acid and dilute sulphuric acid
metal reactivity series and the tendency of metals to form positive ions
displacement reactions and their interpretations based on the reactivity series
prediction of the occurrence of reactions involving metals using the reactivity series
relation between the extraction method of a metal and its position in the metal reactivity series
describe and compare the reactions of some common metals with oxygen/air, water and dilute acids
write the word equations for the reactions of metals with oxygen/air, water and dilute acids
construct a metal reactivity series with reference to their reactions, if any, with oxygen/air, water and dilute acids
write balanced chemical equations to describe various reactions
use the state symbols (s), (l), (g) and (aq) to write chemical equations
relate the reactivity of metals to the tendency of metals to form positive ions
describe and explain the displacement reactions involving various metals and metal compounds in aqueous solutions
deduce the order of reactivity of metals from given information
write balanced ionic equations
predict the feasibility of metal reactions based on the metal reactivity series
relate the extraction method of a metal to its position in the metal reactivity series
Students should learn Students should be able to c. Reacting masses
quantitative relationship of the reactants and the products in a reaction as revealed by a chemical equation
the mole, Avogadro’s constant and molar mass
percentage by mass of an element in a compound
empirical formulae and molecular formulae derived from
experimental data
reacting masses from chemical equations
understand and use the quantitative information provided by a balanced chemical equation
perform calculations related to moles, Avogadro’s constant and molar masses
calculate the percentage by mass of an element in a compound using appropriate information
determine empirical formulae and molecular formulae from compositions by mass and molar masses
calculate masses of reactants and products in a reaction from the relevant equation and state the interrelationship between them
solve problems involving limiting reagents
d. Corrosion of metals and their protection
factors that influence the rusting of iron
methods used to prevent rusting of iron
socioeconomic implications of rusting of iron
corrosion resistance of aluminium
anodisation as a method to enhance corrosion resistance of aluminium
describe the nature of iron rust
describe the essential conditions for the rusting of iron
describe and explain factors that influence the speed of rusting of iron
describe the observations when a rust indicator (a mixture of potassium hexacyanoferrate(III) and phenolphthalein) is used in an experiment that investigates rusting of iron
describe and explain the methods of rusting prevention as exemplified by
i. coating with paint, oil or plastic ii. galvanising
iii. tin-plating iv. electroplating v. cathodic protection vi. sacrificial protection vii. alloying
be aware of the socio-economic impact of rusting
understand why aluminium is less reactive and more corrosion-resistant than expected
describe how the corrosion resistance of
Suggested Learning and Teaching Activities
Students are expected to develop the learning outcomes using a variety of learning experiences. Some related examples are:
searching for and presenting information about the occurrence of metals and their uses in daily life.
analysing information to relate the reactivity of metals to the chronology of the Bronze Age, the Iron Age and the modern era.
designing and performing experiments to extract metals from metal oxides (e.g. silver oxide, copper(II) oxide, lead(II) oxide, iron(III) oxide).
deciding on appropriate methods for the extraction of metals from their ores.
transcribing word equations into chemical equations.
writing balanced chemical equations with the aid of computer simulations.
performing experiments to investigate reactions of metals with oxygen/air, water and dilute acids.
constructing a metal reactivity series based on experimental evidence.
performing experiments to investigate the displacement reactions of metals with aqueous metal ions.
interpreting the observations from a chemical demonstration of the displacement reaction between zinc and copper(II) oxide solid.
writing ionic equations.
performing an experiment to determine the empirical formula of copper(II) oxide.
performing calculations related to moles and reacting masses.
performing an experiment to study the thermal decomposition of baking soda / sodium hydrogencarbonate and solving the related stoichiometric problems.
designing and performing experiments to investigate factors that influence rusting.
performing experiments to study methods that can be used to prevent rusting.
deciding on appropriate methods to prevent metal corrosion based on social, economic and technological considerations.
searching for and presenting information about the metal-recycling industry of Hong Kong and the measures for conserving metal resources in the world.
Values and Attitudes
Students are expected to develop, in particular, the following values and attitudes:
to appreciate the contribution of science and technology in providing us with useful materials.
to appreciate the importance of making fair comparisons in scientific investigations.
to value the need for adopting safety measures when performing experiments involving potentially dangerous chemicals and violent reactions.
to show concern for the limited reserve of metals and realise the need for conserving and using these resources wisely.
to appreciate the importance of the mole concept in the study of quantitative chemistry.
to appreciate the contribution of chemistry in developing methods of rust prevention and hence its socio-economic benefit.
STSE Connections
Students are encouraged to appreciate and to comprehend issues which reflect the interconnections of science, technology, society and the environment. Related examples are:
Although the steel industry has been one of the major profit-making industries in mainland China, there are many constraints on its growth, e.g. the shortage of raw materials in China.
New technologies are being implemented to increase the efficiency of the metal extraction process and at the same time to limit its impact on the environment.
Conservation of metal resources should be promoted to arouse concern for environmental protection.
The development of new alloys to replace pure metals is needed in order to enhance the performance of some products, such as vehicles, aircrafts, window frames and spectacles frames.