OCR 21st Century Science: C3 Chemicals in our lives – risks and benefits
c3_07 Making alkalis
Resources
Student Book pages 184−185  Homework pack c3_07
Files on Teacher Pack c3_07_worksheet; c3_07_technician
Equipment for demonstrations
Learning outcomes
C3.3. 7 understand that the first process for manufacturing alkali from salt and limestone using coal as a fuel
caused pollution by releasing large volumes of an acid gas (hydrogen chloride) creating great heaps of waste that
slowly released a toxic and foul-smelling gas (hydrogen sulfide)
C3.3.8 understand that pollution problems can sometimes be solved by turning wastes into useful chemicals
C3.3.9 understand that oxidation can convert hydrogen chloride to chlorine and that the properties of a compound
are completely different from the elements from which it is made
C3.3.10 recall that chlorine is used to kill microorganisms in domestic water supplies and as a bleach
Ideas about Science
IaS 6.1 science-based technology provides people with many things that they value, and which enhance the
quality of life. Some applications of science can, however, have unintended and undesirable impacts on the quality
of life or the environment – benefits need to be weighed against costs
IaS 6.2 scientists may identify unintended impacts of human activity (including population growth) on the
environment. They can sometimes help us to devise ways of mitigating this impact and of using natural resources
in a more sustainable way
Literacy focus: Developing characters in the drama.
ICT focus: Researching the development of the alkali industry.
In this lesson students are learning to:
 describe the first method of manufacturing alkali and the pollution problems it caused
 explain how one of the pollutants became a source of a useful substance
Obstacles to learning
This lesson may appear unusual to teachers and students, and students may be reluctant to engage in the
discussions and drama, but at its core is the chemistry behind the conversion of natural resources into useful
products and the side-effects that this can have, which teaches us lessons for today.
Stimuli and starter suggestions
 Recap what students have learned earlier in the module. Ask them what they recall about the rocks in NW
England, and the sources and uses of alkalis in early 19th century industry. Finally read out the introduction to
the lesson from Student Book p. 184.
Learning activities
worksheet c3_07
Low demand  Tell the story about Leblanc and Muspratt and the founding of the alkali industry in NW England,
using Student Book p. 184 as a guide. A further interesting point is that the French government was keen to put
Leblanc’s method of alkali production into practice because wars had blocked off supplies of alkali from overseas.
But the French Revolution intervened and this prevented Leblanc from making his fortune. Some points that come
out of the story are: while Britain was in the forefront of industrialisation, France, as the major European power,
was not far behind; Leblanc was the innovator and Muspratt the entrepreneur who made the fortune; wars and
shortages can drive innovation, taxes can delay it; NW England had access to all the raw materials needed but
Glasgow and Teesside also became important sites for the chemical industry. Discuss how people were attracted
to work in the new alkali factories because of the secure wages, but conditions were very poor. Students could do
further research on the development of the alkali industry in the north-west (St. Helens, Widnes, Runcorn). The
Catalyst Museum has resources on this topic. Students may be able to plan a dramatic presentation of the story of
Leblanc, Muspratt and the people of the north-west. The worksheet gives some ideas.
Teaching and learning notes: Students need to draw together the reasons for the importance of the chemical
industry and its beginnings in north-west England. The lesson shows how some knowledge of chemistry has
applications in other areas, such as history and economics.
COLLINS NEW GCSE SCIENCE
© HarperCollinsPublishers Ltd 2011
c3_07 Lesson continued
Standard demand  Further discuss how Muspratt established the Leblanc process. Students do not need detailed
knowledge of the process, other than the raw materials needed – salt, limestone and coal – and the one other
necessary reactant, sulfuric acid. The Leblanc process was complex and extremely inefficient. Most of the raw
materials were wasted as hydrogen chloride gas and a noxious solid called ‘galligu’, which locked up all the sulfur
but gave off poisonous hydrogen sulfide gas in the presence of any acid. The alkali towns rapidly became
environmental disaster sites and the workers and their families suffered dreadful ill-health. Tall chimneys were built
to spread out the hydrogen chloride vapour but they did not solve the problem. Nevertheless, the demand for alkali
meant that the industry grew and more and more people were attracted to the work. The Gossage tower solved the
hydrogen chloride problem, collecting it as hydrochloric acid, but it was 1862 before the Alkali Act forced factory
owners to adopt the process – and then they found they had a market for the hydrochloric acid. Ask students to
research further, finding out more about the Leblanc process, Gossage and the Alkali Acts. They could design a
presentation but a drama is a very good way to present the story – the worksheet gives some ideas.Optionally, you
could demonstrate the production and properties of hydrogen sulfide and hydrogen chloride – see the technician
sheet and do a full risk assessment in advance.
Teaching and learning notes: Students will need to understand that the Leblanc process brought benefits – alkali
for cheaper soaps, glass etc.– as well as serious pollution problems, but that Gossage’s development went some
way to making the process cleaner and more sustainable. Activities 1 and 2 on the worksheet are alternatives. The
drama/presentation may be attempted by all students.
High demand  Explain that hydrochloric acid was a by-product of the Leblanc process but that it was chlorine that
industry needed. Chlorine was used as a bleach in the textile industry before it was used to disinfect water
supplies. A number of reactions were tried to get the chlorine out of the hydrochloric acid; the manganese dioxide
process proved one of the best (Student Book p. 185). Explain that in the reaction the hydrogen in the hydrogen
chloride combines with oxygen to form water. Remind students that this is called an oxidation reaction. Looking at
the reaction in a different way they should see that removing the hydrogen from the hydrogen chloride to leave the
chlorine is another way of describing an oxidation reaction– the worksheet has some questions. Demonstrate a
similar process using potassium manganate(VII) instead of manganese dioxide (see the technician sheet). This
reaction works with only little or no heating. Explain that in this reaction the hydrogen from the hydrogen chloride
combines with oxygen from the manganate, to leave chlorine. Collect some chlorine and demonstrate its properties
– green gas, bleaching agent, (also non-flammable but supports combustion, reactive with metals) – and compare
these with the properties of hydrogen (colourless, flammable, does not affect litmus) and hydrogen
chloride/hydrochloric acid (strong acid but not a bleach) to show that a compound differs from its constituent
elements. Students should record observations and explanations.
Plenary suggestions
Ask students to reflect on the birth of the chemical industry in England. What were the benefits? – new products,
greater wealth, higher standard of living. What were the costs? – pollution, environmental degradation, ill-health.
Who benefited and who suffered? What could be done to improve things? – cleaner, more sustainable processes.
Student Book answers
Q1 Salt was too expensive to use industrially because of the salt tax; an Act ended the tax in 1823.
Q2 Raw materials – salt, coal, limestone; a factory site; workers; buyers.
Q3 Affected by the fumes of hydrogen chloride and hydrogen sulphide generated by the process.
Q4 The alkali manufacturers wouldn’t spend money to clean up their factories if they weren’t forced to.
Q5 Hydrogen and chlorine are gases, colourless and green respectively; chlorine is a bleach; hydrochloric acid is a
solution and is a strong acid.
Q6 Alkali manufacturers were encouraged to collect as much hydrochloric acid as possible to increase their profits;
the factory surroundings were less polluted; people were healthier.
Worksheet answers
Activity 3 (High demand)
Q1 Chlorine was valuable commodity and there was lots of waste hydrochloric acid from the alkali industry;
chlorine is a green gas and a bleach; hydrochloric acid is a colourless solution and a strong acid.
Q2 Hydrogen in the hydrochloric acid is oxidised by gaining oxygen to form water; chlorine is oxidised by loss of
hydrogen.
Q3 Yes and no; the Gossage method had been available for years and there was demand for chlorine; the alkali
manufacturers needed the spur of the law to improve their works.
COLLINS NEW GCSE SCIENCE
© HarperCollinsPublishers Ltd 2011