3.4 Component 4 – Chemistry: Chemistry in our world
Acids react with metals, alkalis and bases to produce compounds known as salts. Many chemical reactions produce a change in temperature. Chemical reactions can be made to go faster or slower by changing the conditions. The Earth’s atmosphere has changed over billions of years. Human activities increase the amounts of some substances in the atmosphere. Water that is safe to drink is essential for human health.
Reactions of acids
Students should have knowledge and understanding of the following content.
| Content | Additional guidance and suggested TDAs | Specification reference GCSE Combined Science: Trilogy | Specification reference GCSE Combined Science: Synergy |
|---|---|---|---|
| Outcome 1 | |||
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Acids react with some metals to produce salts and hydrogen. Hydrochloric acid produces chlorides and sulfuric acid produces sulfates. Students should be able to complete word equations for these reactions, given the names of the reactants. |
Knowledge of reactions is limited to those of magnesium, zinc and iron with hydrochloric and sulfuric acids. |
5.4.2.1 |
4.7.3.1 |
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The test for hydrogen uses a burning splint held at the open end of a test tube of the gas. Hydrogen burns rapidly with a pop sound. |
Suggested activity for TDA Investigate the amount of hydrogen produced when acids react with different metals. |
5.8.2.1 |
4.7.3.1 |
| Outcome 2 | |||
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Acids are neutralised by alkalis (eg sodium hydroxide) and bases (eg insoluble metal oxides) to produce salts and water. |
Household chemicals may be used to illustrate these reactions. |
5.4.2.2 |
4.7.3.2 |
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Acids are neutralised by carbonates to produce salts, water and carbon dioxide. Students should be able to complete word equations for these reactions, given the names of the reactants. Carbon dioxide turns limewater milky. |
Suggested activity for TDA Investigate the reactions of acids with different carbonates. |
5.4.2.2 |
4.7.3.1 |
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Salt solutions can be crystallised to produce solid salts. |
5.4.2.3 |
4.7.3.2 |
Energy and rate of reaction
Students should have knowledge and understanding of the following content.
| Content | Additional guidance and suggested TDAs | Specification reference GCSE Combined Science: Trilogy | Specification reference GCSE Combined Science: Synergy |
|---|---|---|---|
| Outcome 3 | |||
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Some reactions transfer energy to the surroundings so the temperature increases. Such reactions include combustion, oxidation and neutralisation. |
Students are not required to know the term ‘exothermic’. |
5.5.1.1 |
4.7.3.3 |
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Other reactions take in energy from the surroundings, so the temperature decreases. These reactions include dissolving ammonium chloride in water and reacting citric acid with sodium hydrogencarbonate. |
Students are not required to know the term ‘endothermic’. Suggested activity for TDA Compare the temperature changes caused by some reactions. |
5.5.1.1 |
4.7.3.3 |
| Outcome 4 | |||
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The rate of a chemical reaction may be increased by increasing the temperature, increasing the concentration of reactants, increasing the surface area of solid reactants or by adding a suitable catalyst. |
Students do not need to calculate rates of reactions, but should be able to compare relative rates by measuring the time for a reactant to be used up, the volume of a gas produced in a given time, the time for a solution to become opaque or coloured. Suggested activity for TDA Investigate how to make a chemical reaction go faster. |
5.6.1.2 |
4.7.4.6 |
Earth's atmosphere
Students should have knowledge and understanding of the following content.
| Content | Additional guidance and suggested TDAs | Specification reference GCSE Combined Science: Trilogy | Specification reference GCSE Combined Science: Synergy |
|---|---|---|---|
| Outcome 5 | |||
|
During the first billion years of the Earth’s existence, there was intense volcanic activity that released gases that formed the early atmosphere and water vapour that condensed to form the oceans. The early atmosphere was mainly carbon dioxide with little or no oxygen. |
5.9.1.2 |
4.4.1.1 |
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From about three billion years ago, algae and plants developed and produced the oxygen that is now in the atmosphere, by a process called photosynthesis. Photosynthesis can be represented by the word equation: carbon dioxide + water → glucose + oxygen |
Suggested activity for TDA Investigate the production of oxygen by aquatic plants in different conditions by counting bubbles. |
5.9.1.3 |
4.4.1.1 |
| Outcome 6 | |||
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Carbon dioxide was removed from the early atmosphere by dissolving in the oceans and by photosynthesis. Most of the carbon from the carbon dioxide gradually became locked up in rocks as carbonates and fossil fuels. |
5.9.1.4 |
4.4.1.1 |
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The Earth’s atmosphere is now about four-fifths (80%) nitrogen and about one-fifth (20%) oxygen, with small amounts of other gases, including carbon dioxide, water vapour and argon, which is a noble gas. |
Suggested activity for TDA Compare the amount of carbon dioxide in fresh air and exhaled air. |
5.9.1.1 |
Fuels and human impacts on the atmosphere
Students should have knowledge and understanding of the following content.
| Content | Additional guidance and suggested TDAs | Specification reference GCSE Combined Science: Trilogy | Specification reference GCSE Combined Science: Synergy |
|---|---|---|---|
| Outcome 7 | |||
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Crude oil is a mixture of a very large number of compounds. Crude oil is found in deposits underground, eg the oil fields under the North Sea. |
Students will not be required to recall the name of any other fractions. |
5.7.1.1 |
4.8.1.2 |
| Crude oil may be separated into fractions by fractional distillation. This process, which takes place in a refinery, can be used to produce a range of useful fuels and oils, including petrol and diesel. |
5.7.1.2 |
4.8.1.3 |
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| Outcome 8 | |||
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When fuels burn completely the gases released into the atmosphere include carbon dioxide, water (vapour), and oxides of nitrogen. Sulfur dioxide is also released if the fuel contains sulfur. When fuels burn in a limited supply of air carbon monoxide is produced. Solid particles (soot) may also be produced. Students may be required to describe the impact on the environment of burning fossil fuels. Oxides of nitrogen and sulfur dioxide cause acid rain and problems for human health. Carbon monoxide is a colourless, odourless, poisonous gas that can cause death. Solid particles can cause global dimming and problems for human health. |
Suggested activity for TDA Compare the amount of soot produced when burning different fuels. |
5.9.3.2 |
4.4.1.6 |
| Outcome 9 | |||
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Some human activities increase the amounts of greenhouse gases in the atmosphere, such as carbon dioxide from burning fossil fuels and methane from landfill and cattle farming. |
5.9.2.2 |
4.4.1.4 |
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| Increased levels of greenhouse gases in the atmosphere cause the temperature to increase. Many scientists believe that this will result in global climate change. |
5.9.2.3 |
4.4.1.4 |
Water for drinking
Students should have knowledge and understanding of the following content.
| Content | Additional guidance and suggested TDAs | Specification reference GCSE Combined Science: Trilogy | Specification reference GCSE Combined Science: Synergy |
|---|---|---|---|
| Outcome 10 | |||
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Water that is safe to drink has small amounts of dissolved substances and low levels of microbes. Most drinking water is produced by choosing a suitable source of fresh water, filtering to remove solids and sterilising to kill microbes. If supplies of fresh water are limited, salty water can be distilled to produce fresh water. This requires a large energy input. |
Suggested activity for TDA Investigate the amount of dissolved solids in water from different locations by evaporating samples and weighing residues. |
5.10.1.2 |
4.4.1.8 |
