The Ever-Changing Earth (WJEC GCSE Science (Double Award): Chemistry): Flashcards

Wegener used three main types of evidence:

1. Rock layers and mountain ranges that matched across different continents

2. Fossils of the same plants and animals found on different continents

3. Glacial features in tropical regions and coal deposits in Antarctica

False.

Wegener's theory was not accepted because his evidence was all observational and he could not explain the mechanism by which continental drift occurred.

Circular movements of material in the mantle driven by heat from the core. Radioactive decay releases thermal energy, causing less dense material to rise and denser material to sink, which slowly moves the tectonic plates above.

Studies found that rock in the middle of the Atlantic Ocean floor was younger than rock at the edges, and no Atlantic rock samples were older than about 175 million years. This suggested that new ocean floor was being created at the centre and moving outwards, providing evidence for tectonic plate movement.

Radioactive atoms in the Earth's core decay, releasing thermal energy that heats the mantle. This causes convection currents which move the tectonic plates.

False.

Glossopteris fossils were found on five continents: South America, Africa, Asia, Australasia and Antarctica, providing strong support for Wegener's theory.

The lithosphere consists of the crust and the upper mantle. It is the rigid outer layer of the Earth on which the tectonic plates sit.

A plate boundary where two tectonic plates are moving apart. Magma rises to fill the gap, producing new igneous rock. Both volcanic eruptions and earthquakes occur here. The Mid-Atlantic Ridge is an example.

False.

At a conservative boundary, plates slide past each other and no melting occurs, so volcanoes cannot form. Only powerful earthquakes occur at this type of boundary.

At a destructive plate boundary, one tectonic plate is pushed down into the mantle where it melts to form magma.

Scientists plot the epicentres of major earthquakes and the sites of active volcanoes on a world map. Because earthquakes and volcanoes occur at or near plate boundaries, the pattern of these data points reveals the locations of tectonic plates.

A plate boundary where two tectonic plates slide past each other in opposite directions or the same direction at different speeds. Only powerful earthquakes occur here. The San Andreas Fault is an example.

Both constructive and destructive plate boundaries produce volcanic eruptions. At constructive boundaries, lava erupts gently to form new rock as plates move apart. At destructive boundaries, volcanoes are explosive because one plate melts into the mantle as they converge.

True.

At this boundary the Nazca plate is pushed under the South American plate into the mantle, making it a destructive plate boundary that produces both volcanic eruptions and earthquakes.

The Mid-Atlantic Ridge is an example of a constructive plate boundary where new igneous rock is formed.

The atmosphere of the early Earth, thought to have been mainly carbon dioxide and water vapour (similar to Venus and Mars today), with little or no oxygen. It formed from gases released by volcanic eruptions.

In the early atmosphere, water vapour condensed when conditions cooled, forming the oceans. This caused large amounts of CO₂ to dissolve from the atmosphere.

True.

About four-fifths (approximately 78%) of the atmosphere is nitrogen and one-fifth (approximately 21%) is oxygen, with small amounts of carbon dioxide, water vapour and noble gases making up the rest.

Carbon dioxide levels decreased because:

1. CO₂ dissolved in the oceans as water vapour condensed, forming carbonates that were precipitated as sediments

2. Photosynthesis by green plants and algae absorbed CO₂ and released oxygen, locking carbon into living organisms and eventually fossil fuels

Photosynthesis: carbon dioxide + water → glucose + oxygen

Photosynthesis removed CO₂ from the atmosphere and released O₂, causing oxygen levels to increase and carbon dioxide levels to decrease over billions of years.

The combustion of methane: CH₄ + 2O₂ → CO₂ + 2H₂O. This process uses oxygen and releases carbon dioxide into the atmosphere.

True.

In sunlight, ammonia reacted with oxygen to form nitrogen and water. This process reduced ammonia levels and increased the level of nitrogen in the atmosphere.

Fossil fuels contain carbon that was locked up millions of years ago. Burning them releases this carbon as CO₂ into the atmosphere, disturbing the current equilibrium of the carbon cycle and increasing atmospheric carbon dioxide levels, which contributes to global warming.

The process used to separate useful gases in the air, such as nitrogen, oxygen, neon and argon. It works because these gases have different boiling points.

The greenhouse effect is the process by which greenhouse gases such as CO₂ absorb infrared radiation emitted by the Earth's surface and re-emit it in all directions, warming the atmosphere. Increasing CO₂ from burning fossil fuels intensifies this effect, raising the Earth's average temperature.

The combustion of propane: C₃H₈ + 5O₂ → 3CO₂ + 4H₂O. The carbon in the fuel is oxidised during this reaction.

Fossil fuels contain small amounts of sulfur impurities. When these fuels are combusted, the sulfur is oxidised to form sulfur dioxide (SO₂) according to:

S (s) + O₂ (g) → SO₂ (g)

False.

Clean rain is weakly acidic with a pH of approximately 5.5. Acid rain has a much lower pH in the range of 2 to 4 due to dissolved sulfurous and sulfuric acids.

SO₂ dissolves in rainwater to form sulfurous acid. SO₃ dissolves in rainwater to form sulfuric acid. Together these form acid rain.

Three consequences of climate change are:

1. Rising sea levels due to melting polar ice caps and glaciers, increasing flooding

2. Loss of habitats for birds, fish and plants

3. More extreme weather such as storms, heatwaves and changing rainfall patterns

True.

Acid rain reacts with the calcium carbonate (CaCO₃) in limestone and marble, causing stonework to corrode and weaken. This is why acid rain damages buildings and statues.

Fossil fuels (coal, oil and natural gas) all contain carbon, hydrogen and small amounts of sulfur. Combustion oxidises these elements to produce water vapour, carbon dioxide and sulfur dioxide, which contribute to the greenhouse effect and acid rain respectively.

Acid rain falls into rivers and lakes, causing a decrease in pH. The increased acidity affects aquatic life such as fish and other organisms, which can ultimately die if the pH drops too low.

Three measures to reduce CO₂ emissions are:

1. Using hydrogen or renewable energy (solar, wind) instead of fossil fuels

2. Using more fuel-efficient vehicles such as electric or hybrid cars

3. Reducing deforestation and planting more trees to absorb atmospheric CO₂

To reduce acid rain, sulfur dioxide emissions must be reduced. Weak alkalis can be used to neutralise soil and rivers affected by acid rain.

False.

Any method that reduces fossil fuel use will reduce both CO₂ and SO₂ emissions, because sulfur dioxide comes from the sulfur impurities contained within fossil fuels.

Carbon capture and storage is a large-scale method to reduce CO₂ emissions involving three steps:

1. Capture — CO₂ is separated from waste gases

2. Transport — CO₂ is compressed and moved by pipeline, road or ship

3. Storage — CO₂ is injected into rock formations deep underground

In sulfur scrubbing (flue gas desulfurisation), waste gases are passed into a scrubbing chamber where a wet slurry of calcium oxide and calcium carbonate is sprayed over them. The calcium compounds react with the sulfur dioxide to produce calcium sulfate, removing 90–95% of the SO₂ before the gases are released.

Farmers add 'lime' (calcium hydroxide) to their soil to reduce the acidity caused by acid rain.

False.

CCS is only performed on a large scale, for example in coal and natural gas power stations and steel and cement factories. It is not a technology used in private homes.

Acid rain forms because sulfur impurities in fossil fuels are oxidised to sulfur dioxide during combustion, which then dissolves in rainwater. Using low sulfur fuels means less sulfur dioxide is produced, so less acid is formed in the atmosphere and acid rain is reduced.

The limewater test is a chemical test for CO₂: the gas is bubbled through limewater (aqueous calcium hydroxide). A positive result is the limewater turning milky or cloudy, because CO₂ reacts with calcium hydroxide to form a white precipitate of calcium carbonate.

False.

Extinguishing a burning splint only shows a lack of sufficient oxygen — other gases such as nitrogen do this too. The definitive test for CO₂ is bubbling it through limewater, which turns milky or cloudy.

To test for oxygen, a glowing splint is placed in the gas. If oxygen is present, the splint will relight.

The test for carbon dioxide involves bubbling the gas through limewater (aqueous calcium hydroxide solution). The positive result is the limewater turning milky or cloudy.

The test for oxygen involves placing a glowing splint inside a test tube of the gas. The positive result is the splint relighting.

True.

A splint glowing very brightly without fully relighting can indicate the presence of oxygen. In an exam, however, it is best to state that oxygen relights the glowing splint.

Limewater is a solution of calcium hydroxide in water. When CO₂ is bubbled through it, the solution turns milky or cloudy because a white precipitate forms.