C9 - Chemistry Atmosphere

Question 1

What is the composition of the Atmosphere?

Answer 1

Composition of Atmosphere:

• 78% is nitrogen
• 21% is Oxygen
• The rest of the % contains other gases (Carbon dioxide, water vapour and noble gases like argon)

The gases have stayed constant for 200 million years but before that things were different.

Question 2

What was the composition of the early atmosphere?

What do scientists believe about the early atmosphere?

Answer 2

1. During the First billion years there was intense volcanic activity which released large amounts gases and water vapour to form the early atomosphere.
2. As the Earth cooled the water vapour condensed to form the oceans
3. The volcanoes also released large amounts of carbon dioxide with little or no oxygen. In the early stages the atmosphere was mostly carbon dioxide.
4. It was very much like Mars and Venus atmosphere (consisting of mainly carbon dioxide with little to no oxygen.)
5. Some of the carbon dioxide dissolved in the ocean to form a weak acid. This reacted with minerals to form a precipitate and over time formed sediments of carbonated rock on the seabed.(reducing CO2 in air)
6. Then 2.7 billion years ago photosynthetic algae evolved and as a result, photosynthesis produced oxygen and over the next billion years plants formed. This (increased the amount of Oxygen in the atmosphere and decreased CO2 in air.)
7. Volcanoes also produced nitrogen which gradually built up in the atmosphere and there may have been small proportions of methane and ammonia.

Question 3

How did carbon dioxide in the atmosphere decrease?

Answer 3

Algae and plants decreased the percentage of carbon dioxide in the atmosphere by photosynthesis.

Carbon dioxide was also decreased by the formation of sedimentary rocks and fossil fuels that contain carbon.

Question 4

How did oxygen increase and how did it allow life to form?

What did it enable?

Answer 4

Algae and plants produced the oxygen that is now in the atmosphere by photosynthesis, which can be represented by the equation:

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂.
Carbon dioxide + water → Glucose + Oxygen

Algae first produced oxygen about 2.7 billion years ago and soon after this oxygen appeared in the atmosphere. Over the next billion years plants evolved and the percentage of oxygen gradually increased to a level that enabled animals to evolve.

Question 5

Fossil Fuels

Answer 5

• Fossil Fuels are formed over millions of years
• *- They are non-renewable**

Question 6

How is Coal formed?
Why is it formed?

What happens if plants die in marshy wetlands

Answer 6

• Coal is formed from the remains of ferns and trees.
  Overtime, the plants remains are covered with sediment and compressed. High Temp and Pressure creates coal.

If these die in marshy wetlands then they do not decompose.

• That is due to a lack of oxygen or acidic conditions.
• This prevents bacteria from carrying out decomposition.

Question 7

Crude oil

Answer 7

• Crude oil is formed from plankton which are tiny plants and animals found in the sea.
• When they die they set on the seabed.
• If there is no oxygen present then they do not decompose.
• Overtime they are covered with sediment. Heat and pressure convert them into crude oil.

Question 8

How is Limestone formed?

Answer 8

Some of the carbon dioxide in the sea was used to make corals and shells of organisms such as mussels.

When these died these formed sedimentary rock called limestone. Carbon levels falls.

Question 9

How is natural gas formed?

Answer 9

Crude oil and natural gas were formed from simple plants and tiny animals which were living in oceans and lakes. These small organisms died and their remains sank to the bottom where they were buried under sediments. The lack of oxygen prevented oxidation from occurring

Over millions of years, heat and pressure turned the remains of the organisms(such as plankton) into crude oil and natural gas. Natural gas contains the smallest molecules and is often found on top of crude oil, trapped under sedimentary rock.

Question 10

What happens when fuels combust?

Answer 10

Fuels release energy when they are combusted e.g. Coal and Hydrocarbon.

When we burn fuels such as these, the carbon and hydrogen atoms react with oxygen in the air(oxidised). This process is called complete combustion. We know this as CO2 is formed. For It to take place we need plenty of oxygen.

methane + oxygen = Carbon Dioxide + water

If the amount of oxygen is reduced, then we make carbon monoxide instead of carbon dioxide. Carbon monoxide is a toxic gas with no colour and no smell. So many people have carbon monoxide detectors.

Question 11

When is sulphur dioxide produced in combustion:

Answer 11

When coal is burned, sulfur atoms are oxidised which produces sulfur dioxide.

Question 12

When is Nitrogen Oxide produced from combustion?

Answer 12

Oxides of nitrogen are produced in the engine of cars where temperatures are high enough for the nitrogen to react with oxygen.

There is a range of different different molecules that can be produced so scientists call them oxides of nitrogen.

They can cause breathing problems and ACid rain which can kill trees and damage buildings made of limestone.

Question 13

What is soot?

Answer 13

Soot is particles of carbon and unburned hydrocarbons.

They call this type of pollution particulates.

They can damage human health(increasesd risk of Heart disease and lung disease) and cause less energy to reach the earth from the sun. via global dimming

Question 14

How do scientists know the historic composition of the air?

Answer 14

Scientists know the historic composition of the air by analysing the tiny air bubbles trapped in ice cores taken at the poles
The air bubbles were trapped as the snow and ice was laid down tens of thousands of years ago and provide a snapshot of what our atmosphere was like back then

Question 15

How are these pollutants produced:

• *Carbon monoxide and soot**
• *Sulfure Dioxide**

Answer 15

Carbon Monoxide & Soot

• Carbon monoxide is an extremely poisonous gas as it combines with haemoglobin in blood and prevents it from carrying oxygen
• It is particularly malevolent as it is colourless and odourless, making it difficult to detect
• A lack of oxygen supply to the brain can lead to fainting, coma or in worst case scenarios, even death
• The carbon particles released from incomplete combustion clump together to form soot which gradually falls back to the ground
• Soot causes respiratory problems and covers buildings and statues, making them look unclean and accelerating corrosion

Sulfur Dioxide

• Sulfur dioxide is a colourless, pungent smelling gas that is a major air pollutant responsible for acid rain
• The sulfur dioxide released mixes with clouds and readily dissolves in rainwater
• SO₂ is a non-metal oxide so it forms an acidic solution in water, hence forming acid rain
• Acid rain causes corrosion to metal structures, buildings and statues made of carbonate rocks
• It causes damage to aquatic organisms, pollutes crops and water supplies, and irritates lungs, throats and eyes

Oxides of Nitrogen

• Oxides of nitrogen come largely from vehicle exhausts and also contribute to acid rain
• Aside from acid rain, oxides of nitrogen produce photochemical smog and breathing difficulties, in particular for people suffering from asthma