C1 Module Introduction

Transcription

1 OCR 21st Century Science: C1 Air quality C1 Module Introduction Pages in the Student Book provide an introduction to this module. When and how to use these pages These pages summarise what students should already know from KS3 or from previous GCSE units and provide an overview of the content that they will learn in this module. o Use these pages as a revision lesson before you start the first new topic. o Brainstorm everything that students remember about the different topics using the headings as a starting point. Compare your list with the points on page 104. o Use the questions on page 104 as a starting point for class discussions. o Ask students if they can tell you anything about the topics on the right-hand page. o Make a note of any unfamiliar / difficult terms and return to these in the relevant lessons. Suitable answers to the questions on page 104 are: o The smell particles diffuse/move through the air. o Any element, compound and mixture. o Use an indicator (e.g. litmus, methyl orange) solution, or paper/ph indicator a particular colour change shows the presence of an acid, or a ph meter will give a reading below 7; alternatively add a piece of magnesium ribbon or a marble chip (or similar) and look for fizzing. o Lots of possibilities but particularly any activity which involves burning fossil fuels. You could revisit these pages at the following points: o before lesson c1_05 on burning fuels, pages o before lesson c1_09 on removing pollutants, pages Overview of module Students begin by learning about the gases that make up the air, how the composition of the atmosphere changed over time and in particular how humans affect the air with a detrimental effect on air quality. In the second section, students study the sources and processes involving pollutants in the air, using ideas about elements and compounds and the rearrangement of atoms to explain the process of combustion. The final section explores how air quality can be improved by tackling pollution from power stations, reducing the amount of fossil fuels burned and ways of reducing the damaging emissions from vehicles. Obstacles to learning Students may need extra guidance with the following terms and concepts: Gases Students are often misled by diagrams into thinking that the particles in a gas are closer together than they in fact are. Note that percentages of gases in the air are usually given for dry air. The percentage of water vapour is very variable and so is removed from air before accurate analysis takes place. Students may confuse water vapour an invisible gas with clouds, which are droplets of liquid water or ice. The changing atmosphere To understand the past changes in the atmosphere, students need some knowledge of the evolution of organisms and to recognise that the surface of the Earth has not always looked like it does today with trees and flowering plants. Students need to know that scientists accept that geological processes occurring today also took place 4 billion years ago. Concentration data The units used in data on trace gases in the atmosphere can be difficult for students to understand e.g. parts per million, ppm, and micrograms per metre cubed, g/m 3. The concentrations of pollutants (even carbon dioxide) are actually very small and difficult to measure, even though the long-term effects can be severe. Correlations Looking for and explaining links between complex issues like air quality and health demands reading skills and the ability to evaluate evidence. Weaker students may struggle to understand the correlation seen in the patterns.

2 C1 Module Introduction continued Reactants and products Students need a clear understanding of elements and compounds in order to realise that chemical reactions rearrange atoms into new substances without destroying the atoms themselves. Some students find it difficult to recognise that it is just the reorganisation of atoms that gives rise to substances with different properties. Students may also have difficulty with the word property meaning something belonging to, which in science does not mean an object that someone can own, rather the qualities a substance possesses. Reducing emissions There many ideas and technological solutions to the problem and students may get overwhelmed or confused. Practicals in this module In this module students will do the following practical work: o measuring the percentage of oxygen in the air (demonstration) o detecting carbon dioxide in the air (demonstration) o products of combustion (demonstration) o reactions of oxygen o oxidation reactions o measuring mass changes in reactions o combustion of sulfur (demonstration) o observing the properties of iron, sulfur and iron sulfide o collecting and analysing particulate pollution o reactions of sulfur dioxide (Higher tier only) o comparing the efficiency of fuels. Key vocabulary covered in this module gas molecule mean range lava bacteria photosynthesis fossil fuel sediment sedimentary composition carbon monoxide nitrogen oxides sulfur dioxide particulates pollutant correlation smog acid rain hydrocarbon oxidation reduction combustion molecule reactants products element law of conservation of mass products property reactants compound particulates mean range outlier flue-gas desulfurisation biofuels sustainable catalytic converter oxidised reduced

3 OCR 21st Century Science: C1 Air quality C1 Module Checklist Pages in the Student Book provide a student-friendly checklist for revision. When and how to use these pages This checklist is presented in three columns showing progression, based on the grading criteria. Bold italic means Higher tier only. Remind students that they need to be able to use these ideas in various ways, such as: o interpreting pictures, diagrams and graphs o applying ideas to new situations o explaining ethical implications o suggesting some benefits and risks to society o drawing conclusions from evidence they have been given. These pages can be used for individual or class revision using any combination of the suggestions below. o Ask students to construct a mind map linking the points on this checklist. o Work through the checklist as a class and note the points that need further class discussion. o Ask students to tick the boxes on the checklist worksheet (on the Teacher Pack CD) if they feel confident that they are well prepared for the topics. Students should refer back to the relevant Student Book pages to revise the points that they feel less confident about. o Ask students to use the search terms at the foot of the relevant Student Book pages to do further research on the different points in the checklist. o Students could work in pairs, and ask each other what points they think they can do, and why they think that they can do those, and not others.

4 C1 Module Checklist continued Module summary In the introduction to this module, students were presented with a number of new ideas. Work through the list below as part of their revision. Ask students to write their own summaries and mind maps, using this list as a starting point. The air o the air is made up of a mixture of different gases o the air has changed since the Earth was formed o humans are now changing the composition of the air o changing air quality has effects on health Burning fuels o a chemical reaction takes place when fuels burn o rearrangements of atoms take place in chemical reactions o burning fuels containing sulfur produces sulfur dioxide o several pollutants in the air result from burning fossil fuels o pollutants in the air may undergo further reactions Removing pollutants o we are trying to reduce pollutants from power stations o the amount of carbon dioxide we produce needs to be reduced o there are ways of reducing the pollutants given out by vehicles

5 OCR 21st Century Science: C1 Air quality Checklist C1 Aiming for A Use these checklists to see what you can do now. Refer back to the relevant topic in your Student Book if you are not sure. Look across the rows to see how you could progress bold italic means Higher Tier only. Remember that you will need to be able to use these ideas in various ways, such as: interpreting pictures, diagrams and graphs applying ideas to new situations explaining ethical implications suggesting some benefits and risks to society drawing conclusions from evidence that you are given. Working towards an A grade Aiming for Grade C Aiming for Grade A recall that the relative proportions of the main gases in the atmosphere are about 78% nitrogen, 21% oxygen and 1% argon understand that geological processes and living organisms have changed the oceans and the atmosphere over time explain how photosynthesising organisms added oxygen to and removed carbon dioxide from the atmosphere, and how carbon dioxide was removed by dissolving in the oceans and forming sedimentary rocks and fossil fuels explain how human activity has added extra carbon dioxide and small particles of solids (for example carbon) to the atmosphere understand that some of these substances are harmful to the environment and so may cause harm to humans indirectly understand that combustion reactions involve oxidation explain why a substance chemically joining with oxygen is an example of oxidation, why loss of oxygen is an example of reduction, and how this relates to combustion explain how a supply of oxygen can be used to control combustion rates interpret drawings showing the rearrangement and conservation of atoms during a chemical reaction understand that mass is conserved in a chemical reaction, and that the conservation of atoms during combustion reactions means that some atoms in the fuel may react to give products that are pollutants

6 OCR 21st Century Science: C1 Checklist Aiming for Grade C Aiming for Grade A relate the formulas for carbon dioxide, carbon monoxide, sulfur dioxide, nitrogen monoxide, nitrogen dioxide and water to drawings of their molecules recall that particulate carbon is deposited on surfaces; carbon dioxide is used by plants in photosynthesis and dissolves in rain and seawater understand how power station pollution can be reduced by removing sulfur from natural gas and fuel oil, and by removing sulfur dioxide and particulates from flue gases of coal-burning power stations understand how vehicle pollution can be decreased by using more efficient engines, using low-sulfur fuels, using catalytic converters in which nitrogen monoxide is reduced and carbon monoxide is oxidised, and having legal limits to emissions recall that nitrogen monoxide is formed during the combustion of fuels in air, and is subsequently oxidised to nitrogen dioxide, and that NO and NO 2 are jointly referred to as NO x recall that sulfur dioxide and nitrogen dioxide react with water and oxygen to produce acid rain understand how sulfur dioxide is removed from flue gases by reaction with lime or by using seawater understand the benefits and problems of using alternatives to fossil fuels for vehicles, particularly biofuels and electricity

7 OCR 21st Century Science: C1 Air quality Checklist C1 Aiming for C o achieve your forecast grade in the exam you will need Use these checklists to see what you can do. Refer back to the relevant topic in your Student Book if you are not sure. Remember that you will need to be able to use these ideas in various ways, such as: interpreting pictures, diagrams and graphs applying ideas to new situations explaining ethical implications suggesting some benefits and risks to society drawing conclusions from evidence that you are given. Working towards a C grade Aiming for Grade E Aiming for Grade C recall that air forms part of the atmosphere, and is made up of nitrogen, oxygen and argon, plus small amounts of water vapour, carbon dioxide and other gases; recall that this mixture of gases consists of small molecules with large spaces between them recall that the Earth s first atmosphere of mainly carbon dioxide and water vapour was probably formed by volcanic activity, and that when the Earth cooled water vapour condensed to form the oceans understand that human activity has added small amounts of carbon monoxide, nitrogen oxides and sulfur dioxide to the atmosphere describe how some of these substances, called pollutants, are directly harmful to humans recall that coal is mainly carbon and that petrol, diesel and fuel oil are compounds of hydrogen and carbon, called hydrocarbons; recall that hydrocarbons burn to form carbon dioxide and water recall that the relative proportions of the main gases in the atmosphere are about 78% nitrogen, 21% oxygen and 1% argon understand that geological processes and living organisms have changed the oceans and the atmosphere over time explain how human activity has added extra carbon dioxide and small particles of solids (for example carbon) to the atmosphere understand that some of these substances are harmful to the environment and so may cause harm to humans indirectly understand that combustion reactions involve oxidation

8 OCR 21st Century Science: C1 Checklist Aiming for Grade E Aiming for Grade C understand that fuels burn more rapidly in pure oxygen than in air understand that atoms are rearranged during a chemical reaction, and that the numbers of atoms of each element must be the same in the products as in the reactants; understand that the properties of the reactants and products are different explain how a supply of oxygen can be used to control combustion rates interpret drawings showing the rearrangement and conservation of atoms during a chemical reaction understand how burning fossil fuels pollutes the atmosphere with carbon dioxide, sulfur dioxide, carbon monoxide, particulate carbon (from incomplete burning) and nitrogen oxides understand that atmospheric pollutants cannot just disappear, they have to go somewhere understand how pollution caused by power stations can be reduced by using less electricity understand that the only way of producing less carbon dioxide is to burn less fossil fuels; understand how vehicle pollution can be decreased by burning less fuel, using cleaner fuels, and by encouraging the use of public transport relate the formulas for carbon dioxide, carbon monoxide, sulfur dioxide, nitrogen monoxide, nitrogen dioxide and water to drawings of their molecules recall that particulate carbon is deposited on surfaces; carbon dioxide is used by plants in photosynthesis and dissolves in rain and sea water understand how power station pollution can be reduced by removing sulfur from natural gas and fuel oil, and by removing sulfur dioxide and particulates from flue gases of coal-burning power stations understand how vehicle pollution can be decreased by using more efficient engines, using low-sulfur fuels, using catalytic converters in which nitrogen monoxide is reduced and carbon monoxide is oxidised, and having legal limits to emissions

9 OCR 21st Century Science: C1 Air quality C1 Evaluating and analysing evidence Pages in the Student Book prepare students for assessment. When and how to use these pages This activity provides an opportunity to build and assess the skills that students will use when analysing and evaluating data. Ask students to: o read through the context and tasks, listing any terms that they do not understand o as a whole class or in small groups, discuss the tasks to ensure that all students understand the terminology used and to clarify what is required o work individually to answer the questions for each task. If time allows, ask the students to mark one another s work using the mark scheme provided. Notes This activity allows students to analyse information about air pollution from evidence supplied. The tasks encourage students to think about what the evidence shows and the conclusions that they can reasonably draw. The final task asks the wider question of what they might expect to find out from the direct gathering of evidence. The purpose of this is to encourage informed speculation based on the evidence already presented. Answers Task 1 The pattern in the variation of the readings is broadly similar for most of the days shown in that it is at its lowest in the early hours of the morning and highest in the afternoon. This is likely to be because the main causes of the pollution are traffic and industry and the pollutants build up during the course of the day and dissipate overnight. The pattern is broadly similar day by day but not identical. We would expect it to be similar because traffic patterns and industrial activity would be similar during weekdays, but not identical because there will be some changes to these day by day, and also the weather conditions will alter the extent to which the pollution lingers. The levels are also affected by other activities, such as bonfires, which are much less regular. Task 2 It could be expected that bonfires on 5th November would release particulates into the atmosphere but the data shows no sign of this. (Note that the date on the x-axis appears at the start of the 24-hour period). There is a significant rise in particulate levels on the night of 6th November, a Saturday in 2010: the advert for Bonfire Night gives the clue. This shows that bonfires do make a significant difference to pollution levels, but only briefly. Task 3 PM10 particulates are of particular concern because they are too small to be filtered out by nasal hairs and will therefore enter bronchial passages and the lungs, thus potentially affecting breathing and the ability of the body to take in oxygen and release carbon dioxide. A PM10 particulate is 10 micrometres or less across. A micrometre is 10 6 metres, or 10 3 millimetres. Therefore a PM10 particulate is no more than a hundredth of a millimetre across. A hundred of these particulates in a row would fit in a one millimetre division on a ruler. Students should be encouraged both to manipulate the numbers and to find a way of communicating the size in an accessible way. Higher tier candidates should be encouraged to use standard form.

10 C1 Evaluating and analysing evidence continued Task 4 The results are plotted from the hourly averages to avoid the impact of instantaneous high or low figures, such as a large truck passing by the sensor or a sudden gust of wind. It s easier to see the underlying trend if hourly averages are used. Double-sided sticky tape would gather particulates, which could then be counted using a microscope. Replacing the tape every hour would give an indication of the variation over a day; replacing the tape every day would show how it varied over the week. However, it would be difficult to record the number of PM10 particulates because particulates of many sizes would be gathered. Furthermore, counting particulates that have landed in a haphazard way is difficult and not very reliable. The evidence could be used to show that pollution levels rise on Bonfire Night. However the evidence shows that over the course of a year that the impact of regular sources is much greater than the occasional event and that the additional pollution soon clears. Mark scheme For grade E, students should show that they can: o understand that particulates may be released into the atmosphere by humans, and that these can affect air quality o understand how burning fossil fuels pollutes the atmosphere with particulates o identify trends in data displayed in a graph. For grades D, C, in addition show that they can: o understand how human activity has added extra carbon dioxide and small particles of solids (e.g. carbon) to the atmosphere o recall that particulate carbon is deposited on surfaces o suggest explanations for trends in data displayed in a graph o explain the scale of measurement. For grades B, A, in addition show that they can: o understand that some of these substances are harmful to the environment and so cause harm to humans indirectly o effectively convey a sense of scale o suggest how data can be manipulated to indicate underlying trends without being distorted by instantaneous variations.

11 OCR 21st Century Science: C1 Air quality C1 Exam-style questions Pages in the Student Book are exam-style questions. When and how to use these pages These questions are based on the whole of Module C1 and cover a range of different types of questions that students will meet in their written exams. o The questions could be used as a revision test once you ve completed the module. o Work through the questions as a class as part of a revision lesson. o Ask students to mark each other s work, using the mark scheme provided. o As a class, make a list of the questions that most students did not get right. Work through these as a class. Notes on the worked examples The first question looks at the effects of burning fuels containing sulfur. The first part asks students to complete an atom/molecule model diagram for the combustion of sulfur, drawing the SO 2 molecules. They are not asked to write the symbol equation. These diagrams have been used throughout the module to show the rearrangement of atoms in combustion reactions. For part (b) students need to know that sulfur dioxide undergoes oxidation in the air as well as in solution in rain water. In the final part students need to understand that burning coal is responsible for most of the sulfur released into the atmosphere. The second question, for Higher tier students, continues the theme of sulfur pollution. It is a 6-mark question requiring an extended answer. Students need to show knowledge of the processes for removing sulfur dioxide from power station flue gases and also their ability to evaluate the two alternative methods. Students must use correct grammar and spelling, the scientific terms appropriate to this topic and structure their answer suitably to score the quality of written communication marks. Assessment Objectives These exam-style questions cover the Assessment Objectives as described below. AO1 AO2 AO3 Assessment Objectives Recall, select and communicate their knowledge and understanding of science Apply skills, knowledge and understanding of science in practical and other contexts Analyse and evaluate evidence, make reasoned judgements and draw conclusions based on evidence Questions 1, 2a, b, c, 4a, b worked examples 1a, b, 2 2d, 3, 5 worked example 1c 4c worked example 2 Answers These answers are also supplied on the Teacher Pack CD so that students can mark their own or their peer s work. Question number Answer Additional notes Mark 1a Oxygen 21, carbon dioxide, very much less than 1, nitrogen 78, argon about 1 1 mark for each correct match max. 3 3 b Oxygen 1 c Valid points: Carbon dioxide concentration has increased; source burning fossil fuels. Other gases: carbon monoxide from incomplete combustion, nitrogen oxides from reactions in hot furnaces/engines, sulfur dioxide as a result of sulfur in fuel, methane from agriculture and rotting For 6 marks: answer describes correctly the change and sources for carbon dioxide and at least two other gases. All the information given is relevant, clear, organised and presented in a structured and coherent format. Specialist terms are used appropriately. Few, if any, errors in grammar, punctuation and spelling. 6

12 C1 Exam-style questions continued waste. For 4 marks: answer describes correctly the change for carbon dioxide and one other gas and gives a source. For the most part the information given is relevant and presented in a structured and coherent format. Specialist terms are used for the most part appropriately. There may be occasional errors in grammar, punctuation and spelling. For 2 marks: answer describes correctly the change for one gas and gives a source. Answer may be simplistic. There may be limited use of specialist terms. Errors of grammar, punctuation and spelling may be intrusive. For 0 marks: Insufficient or irrelevant science. Answer not worthy of credit. 2a Carbon dioxide; water 1 mark for each 2 b Molecule diagrams of CO 2 and H 2O 1 mark each for the correct diagrams 2 c Oxidation; combustion 2 d 3a b 20 g of propane has been burnt; mass is not lost / mass of products equals mass of reactants; products have escaped into the air. As the levels of sulfur dioxide go down the deaths from pneumonia go down. An explanation / mechanism for how sulfur dioxide makes pneumonia sufferers more likely to die; other factors that affect cases of pneumonia. Any two of these statements for 2 marks 2 Must refer to the direction of both graphs for 2 marks. Reference to being the same shape sufficient for 1 mark 1 mark for each valid point 2 4a Air 1 b The nitrogen monoxide has lost oxygen. 1 c 5a b Catalyst does not work when car engines are started/cold; hence car exhaust contains pollutants/named gases; many cars are started at a similar time; so increased concentration of pollutant gases; hence air quality poor. Electric cars may improve air quality because they do not burn fuels so do not release pollutants. However, they need electricity that is generated in power stations and if these burn fossil fuels then pollutants are emitted. When biofuels are burned they do not give out pollutants such as particulates or sulfur dioxide, and the carbon dioxide that they give out was taken in when the plants were growing.. However, the processing and transportation of biofuels will cause pollutants that affect air quality. Any 3 valid points

13 OCR 21st Century Science: C1 Air quality c1_01 The percentage of oxygen in air P Measuring the percentage of oxygen in the air Watch the experiment. Wear eye protection. This is what your teacher will do: Pack copper turnings into the glass tube and fit the tube between the two gas syringes. Set one of the syringes at its maximum, empty the other, then seal the apparatus. Heat the copper and pass air from one syringe to the other over the hot copper. Leave the apparatus to cool. Measure the volume of air in the apparatus. Repeat the experiment at least three times. Results Fill in the table below with the measurements when your teacher tells you to do so. Run Volume of air at start (cm 3 ) Why is the copper heated? Volume of air at end (cm 3 ) Change in volume of air (cm 3 ) % oxygen in the air 2 Why are the syringes pushed in one after the other? 3 Why is the final volume of air less than the volume of air at the start? 4 Calculate the percentage of oxygen in each air sample and fill in the last column. 5 Why are the figures in the last column not all the same? 6 Find the mean of the percentages of oxygen in the air.

14 c_01 Percentage of oxygen in air continued Extension 7 What is your best estimate for the true value of the percentage of oxygen in the air? 8 If argon and other gases make up about 1% of the air, calculate the percentage of nitrogen in the air. Draw a pie chart for the composition of the air. 9 What happens to the volume of air in the apparatus during the heating of the copper? Explain your observation. 10 The expected percentage of oxygen is 20 to 21%. What errors could cause the percentage to be a) too low, or b) too high? Suggest improvements to the procedure.

15 OCR 21st Century Science: C1 Air quality c1_02 Changing air

16 c1_02 Changing air continued 1 Timeline labels: sentence starters Complete the sentences in the boxes below. Then cut out the boxes and stick them at the point on the timeline when they happened. There were many volcanoes giving out... The Earth and the atmosphere cooled so... Tiny bacteria-like organisms formed in the oceans and began to... Organisms that had taken in carbon dioxide died and... Shellfish took in carbon dioxide to... At the bottom of the oceans, layers of... Animals evolved in the oceans and on land to breathe... People burn fossil fuels that... 2 Changes in the atmosphere Use the Student Book and the internet to find information on how the atmosphere has changed since the Earth formed. Write brief notes on the timeline diagram to show what happened and when. Make sure you explain: the composition of Earth s early atmosphere how the oceans formed how carbon dioxide was removed from the atmosphere why animals were able to evolve what is causing the atmosphere to change now.

17 c1_02 Changing air continued 3 Changing ideas Discuss the following passage and answer the questions that follow. In the 1950s, many scientists thought that the atmosphere on Earth before life evolved may have resembled the atmosphere on other planets in the Solar System. Jupiter and Saturn have a lot of methane and ammonia in their atmospheres. In 1953, an American, Stanley Miller, performed an experiment in which he passed electric sparks, representing lightning, through a mixture of these gases and water. He found that after a few weeks the mixture contained complex molecules including amino acids, which are the basis of life. Miller concluded that his experiment showed how life started on Earth. Evidence from rocks and present-day volcanoes collected over the past 50 years suggests that the early atmosphere was mainly water vapour and carbon dioxide. Most scientists now accept that Miller s experiment does not suggest how life started on Earth. 1 What changes have there been in the source of evidence about the early atmosphere? 2 Miller s experiment has been repeated many times and gives similar results each time. Why do scientists today not agree with Miller s conclusion? 3 Why did it take a number of years before scientists decided that Miller s experiment was not an accurate model of how life formed on Earth? 4 Do you think that the change in ideas about the Earth s early atmosphere happened quickly or gradually? Explain your answer.

18 OCR 21st Century Science: C1 Air quality c1_03 Humans and the air 1 Fact file on gases added to the air Collect information from the tables to fill out the fact file for each gas. Fact file: carbon dioxide Fact file: nitrogen monoxide Fact file: carbon monoxide Fact file: sulfur dioxide Gas Carbon dioxide Carbon monoxide Nitrogen monoxide Sulfur dioxide Chemical reactions Weak acid; turns lime water cloudy Burns; not an acid Acidic gas Acidic gas Gas Carbon dioxide Carbon monoxide Nitrogen monoxide Sulfur dioxide Natural sources Volcanoes, animals, rotting plants and animals Forest fires Lightning Volcanoes Gas Carbon dioxide Carbon monoxide Nitrogen monoxide Sulfur dioxide Properties No colour or smell No colour or smell Colourless but turns brown in air; Smells like chlorine No colour, strong smell irritates throat

19 c1_03 Humans and the air continued 2 Air quality data Look at air quality data for a place in a city and a place in the country. You can choose your own sites on the air quality website, or use the two shown below. Data from Leominster is a small town in the West Midlands with very little industry. Birmingham is a large city in the West Midlands and is an important industrial centre. Write a report on the air quality at the two sites: Note which gas is being examined. Note the scale of the concentrations of the gas. Describe the changes in the concentration of the gas through the week. Compare the concentrations at the same times at the two sites. Try to give explanations. 3 Carbon dioxide Look at the graph of carbon dioxide concentration on page 111 of the Student Book. 1 Describe the shape of the graph. 2 What prediction could you make about the concentration of carbon dioxide in 2020? 3 Why does the graph zig-zag? 4 By about how much does the concentration of carbon dioxide change on each rise and fall?

20 OCR 21st Century Science: C1 Air quality c1_04 Air quality and health Mexico City fact file Population Mexico City grew from a small town during the 20th century. In 1950, the population was about 2 million. It grew to over 20 million in the 1990s, where it has stayed to the present day. Health Since the 1950s there has been an increasing number of cases of lung diseases including asthma, bronchitis, emphysema and lung cancer. The number of deaths reached a peak in the 1990s. Air quality Up to the 1950s, air quality in Mexico City was good, but by the 1990s there was smog on every day in the year, with the concentrations of nitrogen oxides, sulfur dioxide and particulates many times above the standards set by the World Health Organisation. Recent laws reducing the amount of fossil fuels burned have improved air quality but smog still forms on at least 150 days a year. Smog Smog is formed from the mixture of particulates and gases, such as nitrogen oxides, carbon monoxide and sulfur dioxide, given off by burning fossil fuels particularly coal. It is a mixture of fog and smoke which sometimes is pale brown or yellow in colour. The Great London Smog of 1952 One of the most well-researched examples of poor air quality is the Great Smog that enveloped London in December London was one of the largest cities in the world with a population over 10 million. For over 100 years millions of homes, factories and offices had been burning coal for heating. The smoke from the fires contained sulfur dioxide and particulates, which reacted to form a yellow/brown smog that often hung in the air, especially in winter. At the beginning of December 1952, the weather was cold and calm and the smog got thicker and thicker, day after day, even seeping through doors and windows into buildings. People stayed indoors or covered their mouths to avoid breathing the stinking air which irritated the throat. Eventually, on the night of the 9th December, a strong wind blew and cleared the air. Date: Dec Particulates (g/m 3 ) Sulfur dioxide (ppb) Deaths per day

21 c1_04 Air quality and health continued 1 Air quality in Mexico City Cut out the boxes of the Mexico City fact file and stick them in your exercise book or on a sheet of paper. Read them and answer these questions. 1 When was air quality in Mexico City at its worst? 2 Why did air quality in Mexico City get worse after 1950? 3 When did most people die from lung diseases? 4 Why do you think there is a correlation between the number of deaths and air quality? 2 A tale of two cities Read the facts in the Mexico City fact file and write an article for a magazine describing what the air quality is like in Mexico City. Explain why you think there is, or is not, a correlation between air quality and deaths from breathing diseases. Explain why poor air quality may not be the cause of deaths. Plot graphs or charts of the data for the Great London Smog. Put the date on the horizontal axis. Put the particulates, sulfur dioxide and daily deaths on the vertical axis. Then answer these questions: 1 The smog started on 5th December. What was the range of the number deaths each day for the days before the smog began? 2 Describe what the air quality was like before the smog began. 3 The smog cleared on 10th December. What happened to the air quality after the smog cleared? 4 Is there evidence of a correlation between air quality and deaths? Would you say that poor air quality causes deaths? 3 Analysis of the Great London Smog 1 What was the mean number of deaths per day from 1st to 4th December? 2 What was the number of extra deaths on each day from 5th to 15th December? 3 What was the total number of extra deaths during the smog (5th to 9th December)? 4 Did the number of deaths per day return to normal after the smog cleared? 5 One report on the London Smog disaster said that the number of deaths caused by the smog was over Another report said it was up to Which figure do you think is correct? Explain your answer. 6 Does the data give evidence of a correlation between the London Smog and deaths from lung diseases? Is there evidence that the smog was the cause of death?

22 c1_05 Burning fuels OCR 21st Century Science: C1 Air quality 1 The products of combustion Watch the demonstration and answer the following questions. 1 What happens to the substance in the U-tube?. 2 What happens to the limewater?.. 3 Fill in the gaps in the sentences below: The candle is a hydrocarbon.. A hydrocarbon is a. made up of. and... The change in the U-tube shows that is given off. The change to the limewater shows that is given off. 4 Which gas in the air has the fuel combined with?

23 c1_05 Burning fuels continued 2 Combustion an oxidation reaction Priestley and Lavoisier Joseph Priestley was one of many scientists in the 1770s who thought that a substance, called phlogiston, was given off when substances burned. He did a lot of experiments to see what happened when substances were heated. One day he heated mercury in air to make a red powder. He thought the red powder was the ash left when the mercury had lost all its phlogiston. Nevertheless, he heated the red powder again in a glass flask and was surprised to find that it gave off a gas. He collected the gas and found that a candle and a wooden spill burned brightly in it. A mouse breathed the gas quite happily. Later, Priestley visited Lavoisier in Paris and told him about his experiment. Lavoisier repeated it and worked out a new theory of what was happening. He called the new gas oxygen, and said that when substances are heated in air they combine with the oxygen that is in it to form compounds that he called oxides. This reaction is called oxidation. The red powder is mercury oxide, which loses oxygen when it is heated. This is called reduction. 1 What are the differences between Lavoisier s theory and the older theory that Priestley accepted? 2 Complete the word equations for the two parts of Priestley s and Lavoisier s experiment: A Mercury + mercury oxide B Mercury oxide + Which reaction is oxidation? Which reaction is reduction? Practical: Observing combustion reactions Equipment and materials Bunsen burner bench mat tongs goggles lab coat Test materials: magnesium copper iron WARNING: Do not look at magnesium directly when it is burning. Task Use the tongs to hold one of the test materials in a blue Bunsen flame. Observe what happens. Results Make a table like this and write your observations in it.. Test material Appearance before heating Appearance in flame Appearance after heating 3 Why are these reactions described as oxidation reactions? 4 Write word equations for the reactions.

24 c1_05 Burning fuels continued 3 Pure oxygen By 1800, most scientists accepted Lavoisier s theory. His book was popular and his experiments had been repeated many times. Other reactions could be explained better by his oxygen theory, such as the increase in mass when metals are burned. Priestley, however, never gave up his Phlogiston theory before he died aged 71 in Why was Lavoisier s oxygen theory a better theory than the one Priestley accepted? 2 What reasons are possible for Priestley not accepting Lavoisier s theory? 3 Why did most scientists accept Lavoisier s theory after a relatively short time?

25 OCR 21st Century Science: C1 Air quality c1_06 Burning magnesium P How does the mass of reactants change? Equipment and materials Bunsen burner tripod and triangle tongs crucible and lid magnesium ribbon access to balance You must wear eye protection when carrying out this experiment. Method 1 Weigh a crucible and lid. 2 Loosely coil up a piece of magnesium ribbon and put it in the crucible. Weigh the crucible, lid and magnesium. 3 Put the crucible on the triangle on the tripod and heat it strongly for a few minutes. 4 Carefully lift the lid from time to time to see if the magnesium is burning but don t let any smoke escape. 5 When it looks as if all the magnesium has reacted, stop heating and let the crucible cool. 6 Weigh the crucible, lid and the contents left behind. Draw a results table to record all your measurements. Questions 1 What has happened to the magnesium atoms? 2 Did the mass you measured increase, decrease or stay the same? 3 Write a word equation and sketch a diagram showing what happened in the reaction. 4 Explain why the masses you recorded may not be the true values. Extension 5 Calculate: the mass of magnesium you used the final mass of the powder left in the crucible after heating the change in mass the percentage change in mass = final mass 100% mass of magnesium Compare your percentage change with others in your class. Are the values the same? If not, try to explain why not. 6 How could you find the true value for the percentage change? 7 Explain how this experiment supports the law of conservation of mass.

26 OCR 21st Century Science: C1 Air quality c1_06 Rearranging atoms 1 Atoms and molecules 1 Look at the diagrams of molecules and complete the table: Compound carbon dioxide water methane Element carbon oxygen hydrogen oxygen carbon hydrogen Number of atoms of the element in the compound 2 Look at the reaction shown in the diagram below: Which substances are the reactants?.. Which substances are the products? a) Complete the table: number of hydrogen atoms number of oxygen atoms Reactants Products b) What do you notice about the number of hydrogen atoms in the reactants and the products in the table? c) What can you say about the number of oxygen atoms and hydrogen atoms in the reactants and products? 3 When copper is heated in air it gets coated with black copper oxide. Describe what happens to the copper atoms and the molecules of oxygen in the air during this reaction.

27 OCR 21st Century Science: C1 Air quality c1_07 Reactants and products P Investigating the compounds of sulfur Equipment and materials Bunsen burner 5 test tubes test tube rack tongs small spatula mineral wool iron powder sulfur powder mixture of iron and sulfur powder iron sulfide powder magnet You must wear eye protection when carrying out this experiment. Method 1 Put small samples (about half a spatula) of the iron powder, the sulfur powder, the mixture of iron and sulfur and the iron sulfide in four separate test tubes. Describe the appearance of each substance. 2 Run the magnet up and down the outside of each test tube and record what happens. 3 Add about half a test tube of water to each test tube. Shake each tube gently and then let it settle. Record what you see. 4 Using the spatula, put a small amount of the iron and sulfur mixture in a clean, dry test tube. Plug the end of the tube with mineral wool. Using tongs, hold the bottom of the tube in the Bunsen burner flame. As soon as you see something begin to change take the test tube out of the flame and watch it. Record your observations. Results Write your observations in the table: Appearance Magnet Water Heat Iron The colour is... The... is / is not attracted to the magnet It floats /sinks Sulfur The colour is... The... is / is not attracted to the magnet It floats /sinks Iron/sulfur mixture Iron sulfide The colour is... The colour is... The... is / is not attracted to the magnet The... is / is not attracted to the magnet It floats /sinks The powder turned It floats /sinks......

28 c1_07 Reactants and products continued Questions When iron and sulfur are heated they form iron sulfide. 1 What did you see that suggested a chemical reaction was taking place? Compare the properties of the product iron sulfide and the reactants, iron and sulfur. Colour: Magnetism: Behaviour in water: Write a word equation for the reaction Are the properties of : a) the compound iron sulfide... b) the iron/sulfur mixture... similar to or different from the elements iron and sulfur? Explain your answer

29 OCR 21st Century Science: C1 Air quality c1_08 Sources of pollutants Data on the sources of air pollutants Table A: Fossil fuels and pollutants This table shows the percentage of each pollutant that is produced by burning different types of fossil fuels. A certain amount of the pollutant is produced from other sources. Source of % of pollutant produced by burning each type of fuel (2005) pollutant carbon carbon nitrogen sulfur particulates dioxide monoxide oxides dioxide coal oil (petrol, diesel, fuel oil) natural gas other sources (Source: UK emissions of air pollutants , AEA Energy and Environment) Table B: Vehicle emissions This table gives the pollutant emissions by some cars available in Engine size (litres) Pollutant gases carbon dioxide (g/km) Vehicle carbon monoxide nitrogen oxides (mg/km) (mg/km) Aston Martin DB9 Ford Ka Ford Mondeo Land Rover Discovery 4 Mini Volvo V (Source: VCA Car Fuel Data, Department for Transport) 1 Looking at pollutants 1 Look at Table A. Plot a bar chart of the source of pollutant and percentage of carbon dioxide and carbon monoxide formed. 2 Look at Table A and your bar chart from question 1. Which source produces the biggest percentage of: a) carbon dioxide... b) carbon monoxide... c) sulfur dioxide... d) nitrogen oxides... e) particulates?... Highlight on your bar chart the biggest source of each pollutant.

30 c1_08 Sources of pollutants continued 3 Coal and natural gas are used in power stations. Oil is used mainly in transport. Natural gas is burned in homes and factories. Write a sentence about each pollutant gas saying how it is formed. a carbon dioxide b carbon monoxide c sulfur dioxide d nitrogen oxides e particulates Pollutants and molecules 1 Make models of the six molecules given off when fossil fuels are burned carbon dioxide, carbon monoxide, sulfur dioxide, nitrogen oxide, nitrogen dioxide and water. Copy, cut out and join together the templates of atoms shown below. Stick the models alongside your bar chart. 2 Draw a graph of engine size (x-axis) against the amount of carbon dioxide produced (y-axis) for each vehicle in table B. Is there a correlation? If so, describe it. 3 Look at Table B. Compare the amount of pollutants produced with the engine size of the vehicles. Comment on your findings. 4 Use the VCA Car Fuel Data website to look up emission data for other vehicles. Does it fit with your answers to questions 2 and 3 above? carbon nitrogen sulfur oxygen

31 c1_08 Sources of pollutants continued 3 Nitrogen oxides 1 Table B gives data for emissions of nitrogen oxides (or NO x ). Only nitrogen monoxide (NO) is produced in car engines. Is it fair to include all nitrogen oxides in the car emission data? Explain your answer 2 Use the VCA Car Fuel Data website to look up the particulate emissions of diesel engine cars. Is there a pattern?

32 OCR 21st Century Science: C1 Air quality c1_09 Removing pollutants Equipment and materials sticky cards pins or Blu-tack microscope and lamp 1 Collecting particulates Tiny particles of soot and smoke, given off by burning fuels, float in the air until washed out by rain, or they fall on plants or buildings. In this experiment, you will compare the amount of particulates that have been deposited in different locations. Note: steps 1 and 2 take at least 24 hours and must be completed before the rest of the experiment can be done. 1 Put your sticky cards in various places. Note where they are to be left and write the location on the back of the card. 2 Remove the backing tape on each to expose the sticky layer. Leave the sticky cards exposed for at least a day. 3 Collect your sticky cards and make sure you record where each one had been left. 4 Place the sticky card under a microscope and count the number of particles you can see in one square centimetre. Repeat the reading two or three times. Record the numbers. 5 Repeat for other sticky cards or share results with other groups. Place where sticky card was left Number of particles counted in 1 cm Questions 1 Are the numbers all the same for each location? If not, why not? Which place had the highest number of particles on the sticky card? Can you explain why this was?

33 c1_09 Removing pollutants continued 2 Mean and range From your results of the particulate-collecting activity, calculate the mean and range of the number of particles per cm 2 for each location. 1 Which location had the highest mean number of particles per cm 2? Can you give a reason for this? 2 Why is it important to calculate a mean and range for a set of readings? 3 Use an air quality website to find the level of sulfur dioxide and nitrogen oxides pollution in your area and in others. Look at the data recorded for a period. Are variations between readings due to errors in recording or are there valid reasons for the variation? Write a report comparing the data from different places and times and give explanations for the variation. 3 Patterns 1 Look at your particulate pollution data. Which of your results are outliers, if any? What should you do with results that are outliers? 2 Look at the air quality website data across a period of time. Are there patterns in the data? What evidence is there of variation in the measurements? Can you identify any outliers in the measurements? 3 Use the internet to explore the effect of acid rain caused by sulfur dioxide and nitrogen oxide pollution. Produce a presentation or a report on what you discover.

34 OCR 21st Century Science: C1 Air quality c1_10 Removing sulfur dioxide P The reactions of sulfur dioxide solution (Higher tier only) Objectives In this experiment you will look at the reactions used to remove sulfur dioxide from waste gases of coal-fired power stations. Equipment and materials 2 small beakers 100 cm 3 measuring cylinder spatula dropper ph indicator flue-gas solution crushed limestone seawater You must wear eye protection. Method Part 1 1 Measure out 50 cm 3 of flue-gas solution (sulfur dioxide solution) into the beaker. Add a few drops of ph indicator and note the colour. 2 Add a little of the limestone powder using the spatula and stir well. When the reaction has subsided check the indicator colour. 3 Repeat step 2 until the ph indicator shows that all the acidic sulfur dioxide has been used up. Record the appearance during and after the reaction. Part 2 1 Measure out 10 cm 3 of the flue-gas solution (sulfur dioxide solution) into a clean beaker and add a few drops of ph indicator. Note the colour. 2 Add the seawater 5 cm 3 at a time using the dropper until the ph indicator shows that the mixture has become neutral, or slightly alkaline. Note how much seawater was needed. Questions 1 In part 1, how did you know that the sulfur dioxide had been used up? 2 In part 2, how did you know when to stop adding the seawater? 3 For the purposes of this experiment, the sulfur dioxide has already been oxidised to form sulfuric acid. This happens at the end of the processes in power stations. Discuss the differences and similarities in the two reactions and the products of the reactions. Which process do you think is the best? Give your reasons. 4 Find out more about the processes and complete your presentation. The following search terms may be useful: flue-gas desulfurisation limestone flue-gas desulfurisation seawater

35 OCR 21st Century Science: C1 Air quality c1_10 Improving power stations 1 Reducing the use of electricity Investigate ways of reducing the amount of electricity we use which will mean that less pollutants are put into the atmosphere. There are some suggestions below. Putting save electricity in a search engine will give you lots of useful hits. Turn off the TV when it s not being used. Even on standby it uses electricity. Only boil the amount of water you need. When cooking, use the smallest pan you can and boil water in a kettle first. Replace old light bulbs with new low energy bulbs but still turn lights off when you re not in the room. Replace old fridges, freezers and washing machines with new energy-efficient ones. Don t use tumble driers. They use a lot of electricity to dry washing. 2 Removing pollutants Drax Power Station Drax in North Yorkshire is the biggest power station in Britain and one of the biggest coal-fired stations in the world. It produces 6 gigawatts of electricity which is 7% of all the electricity used in Britain. Coal from Yorkshire and Scotland is burned but most of the coal is now imported. Limestone is brought from Derbyshire to remove sulfur dioxide from the waste gases tonnes of limestone are used each week removing tonnes of sulfur dioxide every year. Changing the fuel Since 1980, the way that electricity is produced in Britain has changed. The overall amount of electricity generated has increased by about a quarter. In 1980, coal and oil accounted for 80% of the total now coal and oil produce only about 40% of our electricity. The gap has been filled by natural gas, which was hardly used at all before Nuclear and renewable energy sources make up the final 20%. Research methods of removing pollutants from power station emissions. Produce a presentation of what you find and your opinions of the methods. These search terms may be useful: low-sulfur fuels electrostatic smoke precipitators GCSE flue-gas desulfurisation + power stations (or Drax) 3 Removing sulfur dioxide 1 Read about the chemistry of the two main methods of flue-gas desulfurisation in the Student Book, page 125. Suggest what the benefits and disadvantages of each method might be. 2 Carry out the practical work on practical sheet c1_10 to compare the methods.

36 c1_11 Efficiency of fuels OCR 21st Century Science: C1 Air quality P Comparing fuels Objectives In this activity you will be learning how to: explain how we can minimise the amount of carbon dioxide released from fossil fuel use describe alternative fuels. You will: plan practical ways to answer scientific questions devise appropriate methods for the collection of numerical and other data assess and manage risks when carrying out practical work. Method You are going to compare the energy given out by some different fuels. You will be provided with some burners that contain different fuels. Each has a wick that can be lit and the flame can be used to heat a container of water. Before you start you must answer the following questions. 1 What factors can you compare for the different fuels? 2 What data will you need to gather? 3 How will you gather it? 4 How will you record it? 5 What safety precautions do you need to take? When your answers to these questions have been checked, collect your apparatus and carry out your planned experiment. Comment on what your results show.

37 OCR 21st Century Science: C1 Air quality c1_11 Reducing carbon dioxide 1 Cutting carbon dioxide 1 What are the benefits of walking or cycling on journeys that you might use a car for? Design a poster to encourage people to walk or cycle. Make sure it includes arguments for walking or riding a bike, as opposed to taking a car. 2 On this diagram of a house, write things you could do to reduce the amount of heat lost. 3 Draw up a plan showing how to reduce fossil fuel use one that you could promote to the public.