9 g environmental chemistry

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Chemistry

Environmental Chemistry

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Environmental Chemistry

Acid rain

Summary activities

Greenhouse effect

Soil chemistry

Rocks and weathering

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What is soil?A layer of soil covers much of the Earth’s surface. What is soil made up of?

Plants need soil to grow. How does soil support plant growth?

Soil supplies plants with water and important nutrients and also helps to anchor roots.

weathered rock particles decaying remains of dead plants

and animals (called humus) water air living things, including plants

and animals such as worms

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How are soils different?Soils in different areas are different.

What factors affect the composition and properties of different soils?

The weathered rock particles come from different types of rock and can vary in size.

The amount of humus can vary depending on the plants and animals that lived in the soil.

The amount of water in the soil is affected by the type of rock particles. Clay particles are much smaller than sand. A clay soil is heavier and contains more water than asandy soil which contains lots of room for air.

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The pH of soil affects the availability of nutrients and plants prefer to grow in soils of a certain pH.

pH of different soilsDifferent soils have different pHs.

Soils have different pHs because they are made up of different rocks and so contain different chemicals.

Why do farmers and gardeners need to check soil pH?

For example, strawberries prefer acidic soil and plums prefer alkaline soil.

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Soil pH experiment

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Changing soil pHIf soil is too acidic to grow certain crops, lime can be added.

Lime is a base called calcium oxide. What effect does lime have on the pH of soil?

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Changing soil pHFarmers and gardeners can choose only plants that prefer the pH of their soil.

Alternatively, they can add chemicals that change the soil pH to suit the plants they want to grow.

If soil is too acidic, lime (calcium oxide) is a base that can be added.

The lime neutralizes the acid in the soil and so increases the soil pH.

What type of chemical can be added if soil is too alkaline?

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How do rocks change?Rocks change over time due to environmental conditions such as temperature and acid rain.

The breakdown of rocks into smaller fragments is called weathering.

What are the three types of weathering?

Physical weathering – due to extremes of temperature which can cause freeze-thaw or onion-skin weathering.

Chemical weathering – due to chemical reactions between substances in the rock and acidic rainwater.

Biological weathering – due to the actions of plantsand animals.

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Physical weathering – freeze-thaw weathering

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Physical weathering – onion-skin weathering

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What is acid rain?Normal rainwater has a pH of about 5.6, which means it is naturally slightly acidic.

This natural acidity is due to carbon dioxide which dissolves in rainwater and forms carbonic acid, a weak acid.

Rainwater with a lower pH than normal is called acid rain.

The burning of fossil fuels in power stations and cars forms pollutants such as sulfur dioxide and nitrogen oxides.

These gases dissolve in rainwater to make sulfuric and nitric acids, which are strong acids and so form acid rain.

Why is acid rain a serious environmental problem?

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Acid rain animation

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Effects of acid rainAcid rain has many damaging effects on the environment:

The strong acids in acid rain speed up the chemical weathering of rocks and buildings.

Rivers, lakes and streams become more acidic so that animals and plants cannot live in them.

Soil that becomes more acidic has les nutrients so trees and other plants cannot grow. Acid rain also damages trees by breaking down the waxy coating of leaves.

What can be done to reduce acid rain and its effects?

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Reducing acid rainGovernments are working to reduce the emission of acidic pollutants caused by burning fossil fuels.

Sulfur dioxide is formed when coal containing sulfur is burned in power stations.

This acidic pollutant can be removed from the gases that are released to the atmosphere.

Nitrogen oxides are formed when petrol burns in vehicle engines.

A car’s exhaust system can be fitted with a catalytic converter which turns harmful gases into harmless gases.

How do these changes help to reduce acid rain?

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The greenhouse effectThe atmosphere is a thin layer of gases that surrounds the Earth.

Certain gases in the atmosphere trap some of the heat given off from Earth. This trapped heat is reflected back to the surface and warms the Earth.

The glass in a greenhouse also traps heat inside and so the trapping of heat by the Earth’s atmosphere is called the greenhouse effect.

Without the atmosphere and the greenhouse effect, Earth would be too cold for life to exist!

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The greenhouse effect

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Global warmingCarbon dioxide is the main greenhouse gas involved the warming of the Earth by the greenhouse effect.

Human activity is producing more carbon dioxide and other greenhouse gases.

An increase in the amount of greenhouse gases could increase the amount of heat trapped in the atmosphere.

Some scientists think that this increased greenhouse effect is making the Earth warmer and leading to global warming.

What human activities might contribute to global warming?

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Effects of global warmingIf global warming rises as some scientists predict, it could cause major climate changes:

temperature – some areas may be warmer, others colder;

coastal flooding – sea levels could rise as ocean’s get warmer;

Not all scientists agree about global warming. What evidence is needed to support the theory about global warming?

rainfall – some areas may be wetter and others drier;

plants – some crops may be able to grow better and others not at all.

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Glossaryacid rain – Rainwater that is more acidic than normal

because acidic gases have dissolved in it.

humus – Soil material that is the decaying remains of dead plants and animals.

global warming – The increased greenhouse effect that some scientists think is causing climate change.

greenhouse effect – The warming of the Earth due to the trapping of heat by certain gases in the atmosphere.

greenhouse gases – Gases, such as carbon dioxide and methane, that are involved in the greenhouse effect.

nitrogen oxides – Pollutant gases that mainly come from vehicle engines and form acid rain.

pollutant – A substance which damages the environment.

sulfur dioxide – A pollutant gas that mainly comes fromburning coal in power stations and forms acid rain.