Dual Award Higher tier shaded blue, separate science Chemistry shaded green
| 5.1 Formation and Composition of the Atmosphere | |
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recall that originally the atmosphere of the Earth probably contained methane, ammonia, carbon dioxide and steam |
Discuss the formation of the Earth, the loss of the first primitive atmosphere, and the formation of the atmosphere above solidified molten rocks. |
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explain the origin of the oceans by condensation of steam and their importance as gas reservoirs, particularly for carbon dioxide |
Discuss what happened to the primitive atmosphere as the temperature cooled down: water vapour condensed to form oceans into which soluble gases dissolved (especially CO2). |
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explain that the first primitive plants released oxygen as a result of photosynthesis and that the amount of oxygen gradually increased |
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describe an experiment to determine the approximate percentage of oxygen in the atmosphere |
Discuss possible substances which could remove oxygen from air. |
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recall how to test for carbon dioxide and water |
Discuss tests for CO2 and H2O. |
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recall the composition of the atmosphere |
Discuss gases which are present in the air in small amounts; emphasise that CO2 is present only at a concentration of 0.03%. |
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recall the composition of the atmosphere |
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explain how the carbon cycle helps to maintain atmospheric composition, i.e. carbon dioxide is added to the atmosphere by respiration and combustion and removed by photosynthesis and solution in water |
Discuss the methods by which CO2 is added to and removed from the atmosphere. |
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explain how the carbon cycle helps to maintain atmospheric composition, i.e. carbon dioxide is added to the atmosphere by respiration and combustion and removed by photosynthesis and solution in water |
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5.2 The Nature, Properties and Uses of Noble Gases |
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recall the monatomic nature of noble gases |
Consider the electronic configuration of the elements to elicit the fact that noble gases have eight electrons in their outer shells. |
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explain the monatomic nature of noble gases |
A full outer shell provides the explanation for their monatomic and unreactive nature. |
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relate the uses of noble gases to their physical properties and lack of chemical reactivity |
Obtain ‘Argon’ by breaking a lightbulb around a filemark under water and collecting the gas over an inverted funnel; this can be shown to be unreactive with e.g. burning Mg. |
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5.3 Atmospheric Pollution |
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recall that the combustion of fuels can produce the pollutants: carbon, carbon monoxide, sulphur dioxide and oxides of nitrogen |
Test gas jars of SO2 and NO2 with Universal Indicator paper or solution. |
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recall the ways in which CO, SO2 and NOx are formed and how they are harmful |
Explain the formation of CO, NOx and SO2 in car engines. Discuss how many people in the class are asthmatic and what they think are the reasons for their asthma - this leads to the effects of some of the pollutants. Consider briefly some of the sources other than combustion of fuels in car engines. |
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5.4 Fuels |
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understand that the vapours of volatile flammable materials are more dense than air and pose a fire hazard |
Discuss why naked flames must be extinguished in petrol stations. |
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recall and explain the formation of the products of the complete and incomplete combustion (oxidation) of hydrocarbons |
Recall that the products of complete combustion of hydrocarbon fuels are H2O and CO2. CO and/or C can be formed if insufficient O2 is present. |
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5.5 Energy Changes accompanying Physical and Chemical Changes |
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recall that changes of temperature often accompany reactions |
Demonstrate reactions such as: concentrated H2SO4 added to water, burning Mg, Thermit reaction. |
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define an exothermic reaction as one in which heat energy is given out |
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define an endothermic reaction as one in which heat energy is taken in |
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give examples of exothermic and endothermic processes |
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explain the progress of a reaction, where relevant, in terms of first the breaking of covalent bonds and then the forming of other covalent bonds, (NB. Calculations involving average bond enthalpies (bond energies) are not required) |
Discuss reaction of H2 with O2 to form H2O; for reaction to occur, H-H and O=O bonds have to be broken before O-H bonds formed. |
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recall that the breaking of bonds is endothermic and that the making of bonds is exothermic |
Explain that energy is required to break existing bonds and energy is released when new bonds form. Explain that, in the reaction between H2 and O2, a lighted splint is required to provide energy for breaking existing bonds and energy is given out when new bonds form. |
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understand that most fuels contain carbon compounds and that combustion releases energy, carbon dioxide, and, often, water |
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recall that photosynthesis converts carbon dioxide and water into glucose and oxygen |
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understand that the overall process of photosynthesis is endothermic, that the source of energy is sunlight and that chlorophyll is essential to the process |
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understand that, as regards reactants and products, respiration is effectively the reverse of photosynthesis and is exothermic |
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write balanced equations for the overall processes of respiration and photosynthesis |
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understand the chemical reactions and energy changes involved in the carbon cycle |
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understand that CO2 may be involved in the warming of the Earth's atmosphere (the greenhouse effect) |
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