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Fossil fuels are sources of hydrocarbons and produce CO2 and H2O when burned. Natural gas is mainly methane (CH4). Examples of fossil fuels. Peat, coal, oil

    Chemistry: 10. Air and Oxygen

    Please remember to photocopy 4 pages onto one sheet by going A3?A4 and using back to back on the photocopier

     Syllabus and 21% O, 22OC21 Understand that air is a mixture of gases, and state the composition of air (approximately 78% N

     with CO, water vapour and other gases making up the balance) 2

OC22 Show that approximately one fifth of the air is oxygen; show that there is CO and water vapour in air 2

OC23 Demonstrate and describe what happens when (i) a wooden splint and (ii) a piece of magnesium are burned in

     air

    OC24 Prepare a sample of oxygen by decomposing HO using MnO as a catalyst (word equation and chemical 222

     equation)

OC25 Investigate the ability of oxygen to support combustion in a wooden splint and a candle, and state two uses of

     oxygen

OC26 Burn carbon and magnesium in oxygen, and test the products using moist litmus paper

OC53 Recall that fossil fuels are sources of hydrocarbons, and that they produce CO and HO when burned 22

OC54 List two examples of fossil fuels

    OC55 Describe the role of the combustion of fuels and of SO in the production of acid rain, and describe the effects 2

     of acid rain

OC56 Describe the effect of acid rain on limestone and on plants

OC57 Understand that natural gas is mainly methane

     Student Notes

    Composition of the air

     The atmosphere is made up of 78% nitrogen and 21% oxygen

Carbon dioxide, water vapour and various other gases make up the remainder.

To show that approximately one fifth of the air is oxygen

    Method one

    Set up as shown - the water rises approximately one fifth of the height

    of the graduated cylinder to replace the oxygen used up by the burning

    candle.

Method two 3Volume of air before heating = 100cm 3Volume of air after heating the copper = 79cm 33Volume of oxygen present in 100cm = 21 cm

    Percentage of air = 21/100 = 21%

To show that there is carbon dioxide in air

    When air is drawn through limewater by a vacuum pump the limewater turns milky proving there is carbon dioxide in

    air.

To show that there is water vapour in air

    Fill a test-tube with ice and water and leave it for a few minutes; a liquid will form on the outside of the test-tube.

    Test the liquid using blue cobalt chloride paper it turns pink showing that the liquid was water which condensed.

    1

    Preparation of oxygen

    Hydrogen peroxide oxygen + water

    O ? O + HO 2222 H

Manganese dioxide (MnO) is added in as a catalyst (to speed up the reaction) 2

    Procedure

    1. In this case hydrogen peroxide (labelled X in the diagram) is added to

    manganese dioxide (labelled Y in the diagram).

    2. Oxygen then bubbles through the water in the trough.

    3. Test its pH using universal indicator paper.

    Conclusion: oxygen is a colourless, odourless gas. It has a pH of 7 so it is a

    neutral

To investigate the ability of oxygen to support combustion in a wooden splint and a candle

    Oxygen will relight a glowing splint. This is the characteristic test for oxygen.

Uses of oxygen

    1. Used in welding to increase combustion

    2. Used in medicine to help breathing

    Burning carbon in oxygen

    Heat a piece of carbon over a Bunsen burner and put it into a jar of oxygen.

    Result: The carbon ignites.

    Conclusion: oxygen aids combustion.

    Testing the products

    Add water and test using blue litmus paper.

    It turns red showing that carbon dioxide is an acidic gas.

    Burning magnesium in oxygen

    Hold a piece of magnesium ribbon over a Bunsen burner until it ignites.

    Result: The magnesium burns with a bright flame.

    Testing the products

    Add water and test using red litmus paper.

    It turns blue showing that magnesium oxide is a base.

In general metal oxides tend to be basic and non-metal oxides are acidic

    2

    Fossil fuels

     A fuel is a substance that burns in oxygen to produce heat

     Fossil fuels are fuels that were formed from the remains of plants and animals that lived millions of years ago

Although the three types of fossil fuels (coal, oil and gas) look different, they all contain the same sort of chemicals

    called hydrocarbons.

    Hydrocarbons are compounds that contain hydrogen and carbon only.

     and HO when burned Fossil fuels are sources of hydrocarbons and produce CO22

Examples of fossil fuels Natural gas is mainly methane (CH) 4Peat, coal, oil, natural gas

    Acid Rain

    The role of the combustion of fuels and of sulphur dioxide in the production of acid rain

    Many fossil fuels contain small amounts of sulphur.

    As the fuel gets burnt the sulphur combines with oxygen to from sulphur dioxide (SO) which gets released into the air 2

    When this gas dissolves in water (e.g. rainwater) it forms sulphuric acid, which is corrosive.

    This is the main culprit in acid rain.

     Acid Rain is rain water with a pH of less than 5.5

The effect of acid rain on limestone and on plants

    Acid rain destroys lakes, kills fish and harms trees.

    It corrodes limestone and iron.

Ways to reduce effects of acid rain

    1. Install chemical plants to remove sulfur dioxide from emissions in the chimney of power stations.

    2. Reduce the content of sulfur in fuels like oil and gas. However, this makes them more expensive.

    3. Install catalyst converts in cars to remove harmful oxides of nitrogen from exhaust fumes.

    4. Burn less fossil fuels and use other types of energy such as wind energy, hydroelectric energy, etc.

    3

    Exam Questions

    1. [2008 OL][2009 OL]

    Name any three gases normally found in clean air.

2. [2006]

    The composition of air can be investigated in different ways.

    Two experiments are shown in the diagram.

     3 In Experiment A the air was pushed repeatedly over the heated copper powder and only 79 cmof gas remained at

    the end of the experiment.

    (i) Why is it necessary to let the apparatus cool down before measuring the volume of the remaining gas?

    (ii) Why did the volume of gas decrease and then remain steady? (iii) What is the remaining gas mainly composed of?

    (iv) Experiment B is less accurate than Experiment A.

    Give a reason why this is so.

3. [2006 OL]

    (i) What happens when a “glowing splint” (very hot piece of wood) is placed in a gas jar of oxygen?

    (ii) Give one property of oxygen that this demonstrates.

4. [2008 OL]

    The diagram shows a piece of magnesium being burned in air.

    Magnesium oxide is formed.

    When magnesium oxide is tested with moist red litmus indicator it changes

    colour to blue.

    What does this tell us about magnesium oxide?

5. [2008]

    Magnesium was burned in oxygen as shown in the diagram. (i) What colour was the flame?

    (ii) Pieces of moist blue and red litmus paper were mixed with the product of the combustion.

    What result was seen?

    (iii) What conclusion can be made from the result of the litmus test?

6. [2006]

    In 1774 Joseph Priestley, an English chemist, discovered oxygen. (i) Name the two chemicals that you reacted together to prepare oxygen in the school

    laboratory.

    (ii) One of the chemicals acted as a catalyst.

    Which one of the two chemicals used was the catalyst?

7. [2009]

    Oxygen can be prepared by decomposing liquid A using solid B as

    a catalyst.

    This preparation is shown in the diagram.

    (i) Name liquid A.

    (ii) Name solid B.

    (iii) What is a catalyst?

    4

8. [2006 OL]

    Oxygen gas can be prepared in a school laboratory using the apparatus drawn on

    the right.

    (i) Identify a liquid X and a solid Y that can be used in this preparation.

    (ii) Solid Y speeds up the breakdown of liquid X. What name is given to this type of

    chemical?

    Fossil fuels and acid rain 9. [2007 OL]

    Fossil fuels are sources of hydrocarbons.

    (i) Name one element found in all hydrocarbons.

    (ii) The burning of fossil fuels can give rise to acid rain.

    Give one harmful effect of acid rain.

    (iii) Natural gas is mainly composed of one particular hydrocarbon.

    What is the name of this gas?

10. [2006 OL]

    ). (i) Natural gas is mainly methane (CH4

    Name one of the two elements found in methane.

    (ii) Name one gas produced when methane is burned in air.

11. [2008 OL] Coal

    (i) Choose two fossil fuels from the list on the right. Nuclear

    (ii) Name two products formed when a fossil fuel is burned in air. Oil

     Tidal

    12. [2009 OL]

    (i) Write the letter F beside the name of a fossil fuel in the table. Coal

    (ii) Write the letter P beside a product formed when a fossil fuel is burned. Nuclear Oxygen 13. [2008] Water (i) Natural gas is a fossil fuel. What is a fossil fuel?

    (ii) Name the main constituent of natural gas.

14. [2006]

    (i) Fossil fuels are burnt to provide energy to generate

    electricity.

    Give the name or formula of a compound of sulfur

    formed when a sulphur containing fossil fuel burns

    in air.

    (ii) Acid rain is formed when this sulfur compound

    dissolves in and reacts with water in the

    atmosphere.

    Describe the effect of acid rain on limestone.

15. [2009]

    The photograph shows the emissions from a coal burning electricity generating station.

    Name a pollutant present in the emissions and describe its effect on the environment.

16. [2006]

    In Ireland 90% of electricity is generated by burning fossil fuels compared to other European

    countries who have an average of 50% use of fossil fuels and a 30% use of fossil fuels in the

    USA.

    List two disadvantages, excluding acid rain, of this heavy reliance on fossil fuels for the

    production of electricity.

    5

    Exam Solutions

    1. Carbon dioxide, oxygen, nitrogen, water vapour, helium, ozone

    2.

    (i) Because gases expand on heating which would result in an incorrect reading.

    (ii) Only the oxygen in the air gets removed (used up).

    (iii) Nitrogen

    (iv) A: The gas syringe measures the volume more accurately.

    B: A graduated cylinder is not as accurate as gas syringe.

    3.

    (i) Re-ignites / lights

    (ii) Oxygen supports combustion / substances burn in oxygen

    4. It is basic (alkaline)

    5.

    (i) White

    (ii) Blue stayed blue and red turned blue

    (iii) The product is a base (alkali).

    6.

    (i) Hydrogen peroxide (HO), manganese dioxide (MnO) 222

    (ii) Manganese dioxide (MnO) 2

    7.

    (i) Hydrogen peroxide (HO) 22

    (ii) Manganese dioxide (MnO) 2

    (iii) It is a chemical which speeds up (or slows down) a chemical reaction

    8.

    (i) X: Hydrogen peroxide (HO) Y: Manganese dioxide (MnO) 22 2

    (ii) It is a catalyst

    9.

    (i) Carbon // hydrogen

    (ii) (Damage to buildings / statues / metals / lakes / trees (plants) / fish life / leaches minerals from soil

    (iii) Methane

    10.

    (i) Hydrogen / carbon

    (ii) Carbon dioxide / carbon monoxide / water vapour / steam [accept correct formulae]

    11.

    (i) Coal, Oil

    (ii) Carbon dioxide (CO), water (steam) (HO), sulphur dioxide (SO) 222

    12.

    (i) F: coal

    (ii) P: water

    13.

    (i) It is a fuel produced from dead animals and plants

    (ii) Methane (CH) 4

    14.

    (i) Sulfur dioxide/ SO 2(ii) Acid rain erodes/ dissolves the limestone

    15. Carbon dioxide: global warming/ greenhouse effect.

    Sulphur dioxide: acid rain/ kill plants/ kill fish.

    Smoke: damage to lungs/ lung disease.

    16. CO production, global warming (greenhouse effect), possibly insecure supplies, acidification of oceans, non 2

    renewable, rising fuel (electricity) costs.

    6

    Other Test Questions

    1. What are the four main components of air?

2. What is the approximate percentage of oxygen in air?

3. What is the approximate of nitrogen in air?

4. How would you demonstrate the percentage of air in oxygen?

5. How would you test for carbon dioxide in air?

6. How would you test for water vapour in air?

7. How would you demonstrate what happens when a wooden splint is burned in air?

    8. How would you demonstrate what happens when a piece of magnesium is burned in air?

    9. Draw a labelled diagram of the apparatus used to prepare oxygen gas in the school laboratory.

10. (i) Given the diagram of apparatus used to prepare oxygen

    (ii) Name the liquid and the solid required to produce oxygen in the lab.

    (iii) What is the purpose of the solid?

    (iv) What are such substances called?

    11. Describe using a labelled diagram, how a sample of oxygen could be prepared and collected.

    O using MnO as a catalyst. 12. Describe a laboratory experiment to prepare a sample of oxygen by decomposing H222

13. Give the word equation for this reaction.

14. Give the chemical equation for this reaction.

    15. Describe how you would investigate the ability of oxygen to support combustion in a wooden splint and a candle.

16. Give two uses of oxygen.

    17. How would you test for the products of burning carbon and magnesium in oxygen, using moist litmus paper.

18. A sample of carbon (charcoal) was burnt in oxygen.

    (i) What colour was the carbon?

    (ii) What result was achieved when the compound formed was tested with universal indicator paper?

    (iii) What conclusion can be made about the compound from the result achieved?

19. A sample of carbon(charcoal) was burnt in oxygen.

    The compound formed was tested using blue litmus paper and a colour change was observed.

    (i) What was the colour change?

    (ii) What is the name of the compound formed?

    20. Complete the word equation showing the products formed when a hydrocarbon is burned in oxygen:

    Hydrocarbon + oxygen +

21. What type of fire extinguisher would be suitable for a chip pan fire?

22. What type of fire extinguisher would be suitable for burning fabric or cloth?

23. What are the three conditions are necessary for a fire.

24. What is a catalyst?

    7

25. Three gas jars contain oxygen, hydrogen and carbon dioxide gas.

    (i) How would you identify which one contains oxygen gas?

    (ii) How would you identify which one contains hydrogen gas?

    (iii) How would you identify which one contains carbon dioxide gas?

    (iv) Which of these gases could be used in fire extinguishers?

     3 air was pushed repeatedly over heated copper 26. In an experiment to determine the composition of air, 100cm3powder from one syringe to another. At the end, only 79cm was left.

    (i) Why is it necessary to let the apparatus cool down before measuring the volume of the remaining gas?

    (ii) Why did the volume of gas decrease and then remain steady?

    (iii) What is the remaining gas mostly composed of?

    (iv) A second experiment can be performed to show the composition of air using a burning candle placed inside an

    inverted graduated cylinder placed in a basin of water. This is a less accurate method. Why?

27. (i) Balance the chemical equation for the decomposition of hydrogen peroxide

     HO HO + O2222

    (ii) Name the catalyst used in this experiment.

    (iii) Describe a laboratory test for oxygen gas.

28. When iron is exposed to both water and oxygen, it rusts.

    (i) Draw a diagram to show what would happen when you place steel wool in a test tube and invert it in a basin

    of water.

    (ii) What can be concluded from this experiment?

    Fossil fuels and acid rain

    1. Give one example of a fossil fuel.

2. Write down one harmful effect of acid rain.

3. Identify one gas that causes acid rain.

4. State one way in which acid rain damages the environment.

5. Name one of the gases released when fossil fuels are burnt.

    Describe a harmful effect of this gas.

6. Name a gas that dissolves in rain water to form acid rain

7. Give the name or formula of a compound of sulphur formed when a fossil fuel containing sulphur is burned.

8. What can we do to prevent acid rain?

9.

    (i) What are hydrocarbons?

    (ii) When hydrocarbons are burnt, water vapour is produced. How do we confirm the presence of water vapour. (iii) Identify the black deposit formed on surfaces above the combustion of a hydrocarbon. (iv) What other gas is formed during the combustion of a hydrocarbon?

    (v) How do we test for the presence of this gas?

    8

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