BoS Stage 6 Chemistry Syllabus


Preliminary Course (Year 11)

8.0 Objectives and Outcomes

To be added


8.1 Chemistry Skills

To be added


8.2 The Chemical Earth

To be added


8.3 Metals

To be added


8.4 Water

To be added


8.5 Energy

To be added


HSC Course (Year 12)

9.0 Objective and Outcomes

To be added


9.1 Chemistry Skills

To be added


9.2 Production of Materials

Humans have always exploited their natural environment for all their needs including food, clothing and shelter. As the cultural development of humans continued, they looked for a greater variety of materials to cater for their needs.

The twentieth century saw an explosion in both the use of traditional materials and in the research for development of a wider range of materials to satisfy technological developments. Added to this was a reduction in availability of the traditional resources to supply the increasing world population.

Chemists and chemical engineers continue to play a pivotal role in the search for new sources of traditional materials such as those from the petrochemical industry. As the fossil organic reserves dwindle, new sources of the organic chemicals presently used have to be found. In addition, chemists are continually searching for compounds to be used in the design and production of new materials to replace those that have been deemed no longer satisfactory for needs.

This module increases students' understanding of the implications of chemistry for society and the environment and the current issues, research and developments in chemistry.

9.2.A - Synthetic Polymers

1. Fossil fuels provide both energy and raw materials such as ethylene, for the production of other substances

Students learn to:

  • construct word and balanced formulae equations of chemical reactions as they are encountered

  • identify the industrial source of ethylene from the cracking of some of the fractions from the refining of petroleum

  • identify that ethylene, because of the high reactivity of its double bond, is readily transformed into many useful products

  • identify that ethylene serves as a monomer from which polymers are made

  • identify polyethylene as an addition polymer and explain the meaning of this term

  • outline the steps in the production of polyethylene as an example of a commercially and industrially important polymer

  • identify the following as commercially significant monomers:
    - vinyl chloride
    - styrene
    by both their systematic and common names

  • describe the uses of the polymers made from the above monomers in terms of their properties

Students:

  • gather and present information from first-hand or secondary sources to write equations to represent all chemical reactions encountered in the HSC course

  • identify data, plan and perform a first-hand investigation to compare the reactivities of appropriate alkenes with the corresponding alkanes in bromine water

  • analyse information from secondary sources such as computer simulations, molecular model kits or multimedia resources to model the polymerisation process

 

9.2.B - Biological Polymers

2. Some scientists research the extraction of materials from biomass to reduce our dependence on fossil fuels

Students learn to:

  • discuss the need for alternative sources of the compounds presently obtained from the petrochemical industry

  • explain what is meant by a condensation polymer

  • describe the reaction involved when a condensation polymer is formed

  • describe the structure of cellulose and identify it as an example of a condensation polymer found as a major component of biomass

  • identify that cellulose contains the basic carbon-chain structures needed to build petrochemicals and discuss its potential as a raw material

Students:

  • use available evidence to gather and present data from secondary sources and analyse progress in the recent development and use of a named biopolymer. This analysis should name the specific enzyme(s) used or organism used to synthesise the material and an evaluation of the use or potential use of the polymer produced related to its properties

 

9.2.C - Ethanol

3. Other resources, such as ethanol, are readily available from renewable resources such as plants

Students learn to:

  • describe the dehydration of ethanol to ethylene and identify the need for a catalyst in this process and the catalyst used

  • describe the addition of water to ethylene resulting in the production of ethanol and identify the need for a catalyst in this process and the catalyst used

  • describe and account for the many uses of ethanol as a solvent for polar and non-polar substances

  • outline the use of ethanol as a fuel and explain why it can be called a renewable resource

  • describe conditions under which fermentation of sugars is promoted

  • summarise the chemistry of the fermentation process

  • define the molar heat of combustion of a compound and calculate the value for ethanol from first-hand data

  • assess the potential of ethanol as an alternative fuel and discuss the advantages and disadvantages of its use

  • identify the IUPAC nomenclature for straight-chained alkanols from C1 to C8


Students:

  • process information from secondary sources such as molecular model kits, digital technologies or computer simulations to model:
    - the addition of water to ethylene
    - the dehydration of ethanol

  • process information from secondary sources to summarise the processes involved in the industrial production of ethanol from sugar cane

  • process information from secondary sources to summarise the use of ethanol as an alternative car fuel, evaluating the success of current usage

  • solve problems, plan and perform a first-hand investigation to carry out the fermentation of glucose and monitor mass changes

  • present information from secondary sources by writing a balanced equation for the fermentation of glucose to ethanol

  • identify data sources, choose resources and perform a first-hand investigation to determine and compare heats of combustion of at least three liquid alkanols per gram and per mole

 

9.2.D - Electrochemistry

4. Oxidation-reduction reactions are increasingly important as a source of energy

Students learn to:

  • explain the displacement of metals from solution in terms of transfer of electrons

  • identify the relationship between displacement of metal ions in solution by other metals to the relative activity of metals

  • account for changes in the oxidation state of species in terms of their loss or gain of electrons

  • describe and explain galvanic cells in terms of oxidation/reduction reactions

  • outline the construction of galvanic cells and trace the direction of electron flow

  • define the terms anode, cathode, electrode and electrolyte to describe galvanic cells

Students:

  • perform a first-hand investigation to identify the conditions under which a galvanic cell is produced

  • perform a first-hand investigation and gather first-hand information to measure the difference in potential of different combinations of metals in an electrolyte solution

  • gather and present information on the structure and chemistry of a dry cell or lead-acid cell and evaluate it in comparison to one of the following:
    - button cell
    - fuel cell
    - vanadium redox cell
    - lithium cell
    - liquid junction photovoltaic device (eg the Gratzel cell)
    in terms of:
    - chemistry
    - cost and practicality
    - impact on society - environmental impact

  • solve problems and analyse information to calculate the potential requirement of named electrochemical processes using tables of standard potentials and half-equations

 

9.2.E - Nuclear Chemistry

5. Nuclear chemistry provides a range of materials

Students learn to:

  • distinguish between stable and radioactive isotopes and describe the conditions under which a nucleus is unstable

  • describe how transuranic elements are produced

  • describe how commercial radioisotopes are produced

  • identify instruments and processes that can be used to detect radiation

  • identify one use of a named radioisotope:
    - in industry
    - in medicine

  • describe the way in which the above named industrial and medical radioisotopes are used and explain their use in terms of their properties

 

Students:

  • process information from secondary sources to describe recent discoveries of elements

  • use available evidence to analyse benefits and problems associated with the use of radioactive isotopes in identified industries and medicine

 


9.3 The Acidic Environment

Acidic and basic environments exist everywhere. The human body has a slightly acidic skin surface to assist in disease control and digestion occurs in both acidic and basic environments to assist the breakdown of the biopolymers constituting food. Indeed, microorganisms found in the digestive system are well adapted to acidic or basic environments.

Many industries use acidic and basic compounds for a wide range of purposes and these compounds are found in daily use within the home. Because of this, an awareness of the properties of acids and bases is important for safe handling of materials. Currently, concerns exist about the increased release of acidic and basic substances into the environment and the impact of these substances on the environment and the organisms within those environments.

This module increases students' understanding of the history, nature and practice of chemistry, the applications and uses of chemistry and implications of chemistry for society and the environment.

9.2.B - Identification

1. Indicators were identified with the observation that the colour of some flowers depends on soil composition

Students learn to:

  • classify common substances as acidic, basic or neutral

  • identify that indicators such as litmus, phenolphthalein, methyl orange and bromothymol blue can be used to determine the acidic or basic nature of a material over a range, and that the range is identified by change in indicator colour

  • identify and describe some everyday uses of indicators including the testing of soil acidity/basicity

Students:

  • perform a first-hand investigation to prepare and test a natural indicator

  • identify data and choose resources to gather information about the colour changes of a range of indicators

  • solve problems by applying information about the colour changes of indicators to classify some household substances as acidic, neutral or basic


9.2.A - Synthesis
9.2.C - Equilibrium

2. While we usually think of the air around us as neutral, the atmosphere naturally contains acidic oxides of carbon, nitrogen and sulfur. The concentrations of these acidic oxides have been increasing since the Industrial Revolution

Students learn to:

  • identify oxides of non-metals which act as acids and describe the conditions under which they act as acids

  • analyse the position of these non-metals in the Periodic Table and outline the relationship between position of elements in the Periodic Table and acidity/basicity of oxides

  • define Le Chatelier's principle

  • identify factors which can affect the equilibrium in a reversible reaction

  • describe the solubility of carbon dioxide in water under various conditions as an equilibrium process and explain in terms of Le Chatelier's principle

  • identify natural and industrial sources of sulfur dioxide and oxides of nitrogen

  • describe, using equations, examples of chemical reactions which release sulfur dioxide and chemical reactions which release oxides of nitrogen

  • assess the evidence which indicates increases in atmospheric concentration of oxides of sulfur and nitrogen

  • calculate volumes of gases given masses of some substances in reactions, and calculate masses of substances given gaseous volumes, in reactions involving gases at 0°C and 100kPa or 25°C and 100kPa

  • explain the formation and effects of acid rain

Students:

  • identify data, plan and perform a first-hand investigation to decarbonate soft drink and gather data to measure the mass changes involved and calculate the volume of gas released at 25°C and 100kPa

  • analyse information from secondary sources to summarise the industrial origins of sulfur dioxide and oxides of nitrogen and evaluate reasons for concern about their release into the environment


9.2.D - Behaviour
9.2.E - Analysis

3. Acids occur in many foods, drinks and even within our stomachs

Students learn to:

  • define acids as proton donors and describe the ionisation of acids in water

  • identify acids including acetic (ethanoic), citric (2-hydroxypropane-1,2,3-tricarboxylic), hydrochloric and sulfuric acid

  • describe the use of the pH scale in comparing acids and bases

  • describe acids and their solutions with the appropriate use of the terms strong, weak, concentrated and dilute

  • identify pH as -log10 [H+] and explain that a change in pH of 1 means a ten-fold change in [H+]

  • compare the relative strengths of equal concentrations of citric, acetic and hydrochloric acids and explain in terms of the degree of ionisation of their molecules

  • describe the difference between a strong and a weak acid in terms of an equilibrium between the intact molecule and its ions


Students:

  • solve problems and perform a first-hand investigation to use pH meters/probes and indicators to distinguish between acidic, basic and neutral chemicals

  • plan and perform a first-hand investigation to measure the pH of identical concentrations of strong and weak acids

  • gather and process information from secondary sources to write ionic equations to represent the ionisation of acids

  • use available evidence to model the molecular nature of acids and simulate the ionisation of strong and weak acids

  • gather and process information from secondary sources to explain the use of acids as food additives

  • identify data, gather and process information from secondary sources to identify examples of naturally occurring acids and bases and their chemical composition

  • process information from secondary sources to calculate pH of strong acids given appropriate hydrogen ion concentrations


4. Because of the prevalence and importance of acids, they have been used and studied for hundreds of years. Over time, the definitions of acid and base have been refined

Students learn to:

  • outline the historical development of ideas about acids including those of:
    - Lavoisier
    - Davy
    - Arrhenius

  • outline the Brönsted-Lowry theory of acids and bases

  • describe the relationship between an acid and its conjugate base and a base and its conjugate acid

  • identify a range of salts which form acidic, basic or neutral solutions and explain their acidic, neutral or basic nature

  • identify conjugate acid/base pairs

  • identify amphiprotic substances and construct equations to describe their behaviour in acidic and basic solutions

  • identify neutralisation as a proton transfer reaction which is exothermic

  • describe the correct technique for conducting titrations and preparation of standard solutions

  • qualitatively describe the effect of buffers with reference to a specific example in a natural system

Students:

  • gather and process information from secondary sources to trace developments in understanding and describing acid/base reactions

  • choose equipment and perform a first-hand investigation to identify the pH of a range of salt solutions

  • perform a first-hand investigation and solve problems using titrations and including the preparation of standard solutions, and use available evidence to quantitatively and qualitatively describe the reaction between selected acids and bases

  • perform a first-hand investigation to determine the concentration of a domestic acidic substance using computer-based technologies

  • analyse information from secondary sources to assess the use of neutralisation reactions as a safety measure or to minimise damage in accidents or chemical spills


9.2.F - Esters

5. Esterification is a naturally occurring process which can be performed in the laboratory

Students learn to:

  • describe the differences between the alkanol and alkanoic acid functional groups in carbon compounds

  • identify the IUPAC nomenclature for describing the esters produced by reactions of straight-chained alkanoic acids from C1 to C8 and straight-chained primary alkanols from C1 to C8

  • explain the difference in melting point and boiling point caused by straight-chained alkanoic acid and straight-chained primary alkanol structures

  • identify esterification as the reaction between an acid and an alkanol and describe, using equations, examples of esterification

  • describe the purpose of using acid in esterification for catalysis

  • explain the need for refluxing during esterification

  • outline some examples of the occurrence, production and uses of esters

Students:

  • identify data, plan, select equipment and perform a first-hand investigation to prepare an ester using reflux

  • process information from secondary sources to identify and describe the uses of esters as flavours and perfumes in processed foods and cosmetics



9.4 Chemical Monitoring and Management

The state of our environment is an important issue for society. Pollution of air, land and water in urban, rural and wilderness areas is a phenomenon that affects the health and survival of all organisms, including humans. An understanding of the chemical processes involved in interactions in the full range of global environments, including atmosphere and hydrosphere, is indispensable to an understanding of how environments behave and change. It is also vital in understanding how technologies, which in part are the result of chemical research, have affected environments. This module encourages discussion of how chemists can assist in reversing or minimising the environmental problems caused by technology and the human demand for products and services.

Some modern technologies can facilitate the gathering of information about the occurrence of chemicals — both those occurring in natural environments and those that are released as a result of human technological activity. Such technologies include systems that have been developed to quantify and compare amounts of substances.

This module increases students' understanding of the nature, practice, applications and uses of chemistry and the implications of chemistry for society and the environment.

9.4.A - Chemical Monitoring

1. Much of the work of chemists involves monitoring the reactants and products of reactions and managing reaction conditions

Students learn to:

  • outline the role of a chemist employed in a named industry or enterprise, identifying the branch of chemistry undertaken by the chemist and explaining a chemical principle that the chemist uses

  • identify the need for collaboration between chemists as they collect and analyse data

  • describe an example of a chemical reaction such as combustion, where reactants form different products under different conditions and thus would need monitoring

Students:

  • gather, process and present information from secondary sources about the work of practising scientists identifying:

    - the variety of chemical occupations
    - a specific chemical occupation for a more detailed study

 

9.4.B - Haber Process

2. Chemical processes in industry require monitoring and management to maximise production

Students learn to:

  • identify and describe the industrial uses of ammonia

  • identify that ammonia can be synthesised from its component gases, nitrogen and hydrogen

  • describe that synthesis of ammonia occurs as a reversible reaction that will reach equilibrium

  • identify the reaction of hydrogen with nitrogen as exothermic

  • explain why the rate of reaction is increased by higher temperatures

  • explain why the yield of product in the Haber process is reduced at higher temperatures using Le Chatelier's principle

  • explain why the Haber process is based on a delicate balancing act involving reaction energy, reaction rate and equilibrium

  • explain that the use of a catalyst will lower the reaction temperature required and identify the catalyst(s) used in the Haber process

  • analyse the impact of increased pressure on the system involved in the Haber process

  • explain why monitoring of the reaction vessel used in the Haber process is crucial and discuss the monitoring required

Students:

  • gather and process information from secondary sources to describe the conditions under which Haber developed the industrial synthesis of ammonia and evaluate its significance at that time in world history

 

9.4.C - Ions

3. Manufactured products, including food, drugs and household chemicals are analysed to determine or ensure their chemical composition

Students learn to:

  • deduce the ions present in a sample from the results of tests.

  • describe the use of atomic absorption spectroscopy (AAS) in detecting concentrations of metal ions in solutions and assess its impact on scientific understanding of the effects of trace elements.

Students:

  • perform first-hand investigations to carry out a range of tests, including flame tests, to identify the following ions:
    - phosphate
    - sulfate
    - carbonate
    - chloride
    - barium
    - calcium
    - lead
    - copper
    - iron

  • gather, process and present information to describe and explain evidence for the need to monitor levels of one of the above ions in substances used in society.

  • identify data, plan, select equipment and perform first-hand investigations to measure the sulfate content of lawn fertiliser and explain the chemistry involved.

  • analyse information to evaluate the reliability of the results of the above investigation and to propose solutions to problems encountered in the procedure.

  • gather, process and present information to interpret secondary data from AAS measurements and evaluate the effectiveness of this in pollution control.

9.4.D - Atmospheric Chemistry

4. Human activity has caused changes in the composition and structure of the atmosphere. Chemists monitor these changes so that further damage can be limited.

Students learn to:

  • describe the composition and layered structure of the atmosphere.

  • identify the main pollutants found in the lower atmosphere and their sources.

  • describe ozone as a molecule able to act both as an upper atmosphere UV radiation shield and a lower atmosphere pollutant.

  • describe the formation of a coordinate covalent bond.

  • demonstrate the formation of coordinate covalent bonds using Lewis electron dot structures.

  • compare the properties of the oxygen allotropes O2 and O3 and account for them on the basis of molecular structure and bonding.

  • compare the properties of the gaseous forms of oxygen and the oxygen free radical.

  • identify the origins of chlorofluorocarbons (CFCs) and halons in the atmosphere.

  • identify and name examples of isomers (excluding geometrical and optical) of haloalkanes up to eight carbon atoms.

  • discuss the problems associated with the use of CFCs and assess the effectiveness of steps taken to alleviate these problems.

  • analyse the information available that indicates changes in atmospheric ozone concentrations, describe the changes observed and explain how this information was obtained.

Students:

  • analyse the information available that indicates changes in atmospheric ozone concentrations, describe the changes observed and explain how this information was obtained.

  • present information from secondary sources to write the equations to show the reactions involving CFCs and ozone to demonstrate the removal of ozone from the atmosphere.

  • gather, process and present information from secondary sources including simulations, molecular model kits or pictorial representations to model isomers of haloalkanes.

  • present information from secondary sources to identify alternative chemicals used to replace CFCs and evaluate the effectiveness of their use as a replacement for CFCs.

9.4.E - Water Quality

5. Human activity also impacts on waterways. Chemical monitoring and management assists in providing safe water for humans to use and to protect the habitats of other organisms.

Students learn to:

  • identify that water quality can be determined by considering:
    - concentrations of common ions
    - total dissolved solids
    - hardness
    - turbidity
    - acidity
    - dissolved oxygen and biochemical oxygen demand

  • identify factors that affect the concentrations of a range of ions in solution in natural bodies of water such as rivers and oceans.

  • describe and assess the effectiveness of methods used to purify and sanitise mass water supplies.

  • describe the design and composition of microscopic membrane filters and explain how they purify contaminated water.

Students:

  • perform first-hand investigations to use qualitative and quantitative tests to analyse and compare the quality of water samples.

  • gather, process and present information on the range and chemistry of the tests used to:
    - identify heavy metal pollution of water
    - monitor possible eutrophication of waterways

  • Gather, process and present information on the features of the local town water supply in terms of:
    - catchment area
    - possible sources of contamination in this catchment
    - chemical tests available to determine levels and types of contaminants
    - physical and chemical processes used to purify water
    - chemical additives in the water and the reasons for the presence of these additives

 


9.5 Industrial Chemistry

Industry uses chemical reactions to produce chemicals for use by society. This module develops the ideas that some chemicals have been produced to replace naturally occurring chemicals that are no longer available or are not economically viable. The concepts of qualitative and quantitative equilibrium are further developed.

Industrial chemical processes cover the full range of reactions but concentration on some case studies is sufficient to illustrate the range of reactions and the role of chemists and chemical engineers involved in these processes. This allows some insight into the qualitative and quantitative aspects of the chemical industry and allows a consideration of the analytical processes and monitoring that are necessary for efficient production.

This module increases students' understanding of the history, applications and uses of chemistry, and current issues, research and developments in chemistry.

9.5.A - Replacement Products

9.5.1 Industrial chemistry processes have enabled scientists to develop replacements for natural products

Students learn to:

  • discuss the issues associated with shrinking world resources with regard to one identified natural product that is not a fossil fuel, identifying the replacement materials used and/or current research in place to find a replacement for the named material

Students:

  • identify data, gather and process information to identify and discuss the issues associated with the increased need for a natural resource that is not a fossil fuel and evaluate the progress currently being made to solve the problems identified

9.5.B - Quantitative Equilibrium

2. Many industrial processes involve manipulation of equilibrium reactions

Students learn to:

  • explain the effect of changing the following factors on identified equilibrium reactions

    - pressure
    - volume
    - concentration
    - temperature

  • interpret the equilibrium constant expression (no units required) from the chemical equation of equilibrium reactions

  • identify that temperature is the only factor that changes the value of the equilibrium constant (K) for a given equation

Students:

  • identify data, plan and perform a first-hand investigation to model an equilibrium reaction

  • choose equipment and perform a first-hand investigation to gather information and qualitatively analyse an equilibrium reaction

  • process and present information from secondary sources to calculate K from equilibrium conditions

9.5.C - Sulfuric Acid

3. Sulfuric acid is one of the most important industrial chemicals

Students learn to:

  • outline three uses of sulfuric acid in industry

  • describe the processes used to extract sulfur from mineral deposits, identifying the properties of sulfur which allow its extraction and analysing potential environmental issues that may be associated with its extraction

  • outline the steps and conditions necessary for the industrial production of H2SO4 from its raw materials

  • describe the reaction conditions necessary for the production of SO2 and SO3

  • apply the relationship between rates of reaction and equilibrium conditions to the production of SO2 and SO3

  • describe, using examples, the reactions of sulfuric acid acting as:

    - an oxidising agent
    - a dehydrating agent

  • describe and explain the exothermic nature of sulfuric acid ionisation

  • identify and describe safety precautions that must be taken when using and diluting concentrated sulfuric acid

Students:

  • gather, process and present information from secondary sources to describe the steps and chemistry involved in the industrial production of H2SO4 and use available evidence to analyse the process to predict ways in which the output of sulfuric acid can be maximised

  • perform first-hand investigations to observe the reactions of sulfuric acid acting as:

    - an oxidising agent
    - a dehydrating agent

  • use available evidence to relate the properties of sulfuric acid to safety precautions necessary for its transport and storage

9.5.D - Sodium Hydroxide

4. The industrial production of sodium hydroxide requires the use of electrolysis

Students learn to:

  • explain the difference between galvanic cells and electrolytic cells in terms of energy requirements

  • outline the steps in the industrial production of sodium hydroxide from sodium chloride solution and describe the reaction in terms of net ionic and full formulae equations

  • distinguish between the three electrolysis methods used to extract sodium hydroxide:

    - mercury process
    - diaphragm process
    - membrane process

    by describing each process and analysing the technical and environmental difficulties involved in each process

Students:

  • identify data, plan and perform a first-hand investigation to identify the products of the electrolysis of sodium chloride

  • analyse information from secondary sources to predict and explain the different products of the electrolysis of aqueous and molten sodium chloride

9.5.E - Saponification

5. Saponification is an important organic industrial process

Students learn to:

  • describe saponification as the conversion in basic solution of fats and oils to glycerol and salts of fatty acids

  • describe the conditions under which saponification can be performed in the school laboratory and compare these with industrial preparation of soap

  • account for the cleaning action of soap by describing its structure

  • explain that soap, water and oil together form an emulsion with the soap acting as an emulsifier

  • distinguish between soaps and synthetic detergents in terms of:

    - the structure of the molecule
    - chemical composition
    - effect in hard water

  • distinguish between anionic, cationic and non-ionic synthetic detergents in terms of:

    - chemical composition
    - uses

Students:

  • perform a first-hand investigation to carry out saponification and test the product

  • gather, process and present information from secondary sources to identify a range of fats and oils used for soap-making

  • perform a first-hand investigation to gather information and describe the properties of a named emulsion and relate these properties to its uses

  • perform a first-hand investigation to demonstrate the effect of soap as an emulsifier

  • solve problems and use available evidence to discuss, using examples, the environmental impacts of the use of soaps and detergents

9.5.E - Sodium Carbonate

6. The Solvay process has been in use since the 1860s

Students learn to:

  • identify the raw materials used in the Solvay process and name the products

  • describe the uses of sodium carbonate

  • identify, given a flow chart, the sequence of steps used in the Solvay process and describe the chemistry involved in:

    - brine purification
    - hydrogen carbonate formation
    - formation of sodium carbonate
    - ammonia recovery

  • discuss environmental issues associated with the Solvay process and explain how these issues are addressed

Students:

  • perform a first-hand investigation to assess risk factors and then carry out a chemical step involved in the Solvay process, identifying any difficulties associated with the laboratory modelling of the step

  • process information to solve problems and quantitatively analyse the relative quantities of reactants and products in each step of the process

  • use available evidence to determine the criteria used to locate a chemical industry using the Solvay process as an example