Air and water

Question 1

What is the evidence for the composition of the early atmosphere?

Answer 1

Very limited evidence due to its occurrence about 4.6 billion years ago.

Question 2

How did the early atmosphere likely compare to the atmospheres of Mars or Venus?

Answer 2

It consisted mostly of carbon dioxide with little or no oxygen gas and nitrogen.

Question 3

What role did volcanic activity play in the formation of the early atmosphere?

Answer 3

Released mainly carbon dioxide and water vapour, gradually producing nitrogen.

Question 4

What small proportions of gases may have been present in the early atmosphere?

Answer 4

• Methane
• Ammonia

Question 5

How were the oceans formed?

Answer 5

From temperatures cooling, causing water vapour to condense into water.

Question 6

What process led to the decrease of carbon dioxide in the atmosphere?

Answer 6

Carbon dissolved in water, forming carbonates that produced sediments.

Question 7

When did photosynthetic organisms first begin to produce oxygen?

Answer 7

About 2.7 billion years ago.

Question 8

What is the equation for photosynthesis?

Answer 8

6CO2 + 6H2O → C6H12O6 + 6O2

Question 9

How did photosynthesis contribute to the atmosphere’s oxygen levels?

Answer 9

Produced oxygen and decreased carbon dioxide.

Question 10

What are two additional ways carbon dioxide levels were decreased in the atmosphere?

Answer 10

• Formation of sedimentary rocks
• Formation of fossil fuels

Question 11

What has been the proportion of gases in the atmosphere for the past 200 million years?

Answer 11

About 78% nitrogen and 21% oxygen and 1% argon with small proportions of various other gases

This includes carbon dioxide, water vapour, and noble gases.

Question 12

What is potable water?

Answer 12

Water that is safe to drink

Potable water needs to have sufficiently low levels of dissolved salts and microbes.

Question 13

Is potable water pure water in the chemical sense?

Answer 13

No

Potable water contains dissolved substances.

Question 14

What provides fresh water in the UK?

Answer 14

Rain

Rain provides water with low levels of dissolved substances that collects in the ground and in lakes and rivers.

Question 15

What is the first step in making fresh water safe to drink?

Answer 15

Passing it through filter beds

This typically includes a wire mesh followed by a bed of sand or gravel.

Question 16

What is the purpose of sterilisation in water treatment?

Answer 16

To kill the microbes in the water

Sterilising agents can include chlorine, ozone, or ultraviolet light.

Question 17

What may be required if there are limited supplies of fresh water?

Answer 17

Desalinisation of salty or sea water

Desalinisation can be done by distillation or reverse osmosis.

Question 18

How is reverse osmosis performed?

Answer 18

At high pressure, forcing water against the normal osmotic gradient across very fine membranes

This process allows only water to cross, leaving dissolved ions behind.

Question 19

What are the energy requirements of desalinisation processes?

Answer 19

They require large amounts of energy

Filtration and sterilisation may also still be needed after these processes.

Question 20

What types of waste require treatment before being released into the environment?

Answer 20

Sewage and agricultural waste water

Treatment is necessary due to organic matter and harmful microbes.

Question 21

What needs to be removed from sewage and agricultural waste water?

Answer 21

Organic matter and harmful microbes

This is crucial for environmental safety.

Question 22

What is required for the treatment of industrial waste water?

Answer 22

Removal of organic matter and harmful chemicals

Question 23

What is the first step in the sewage treatment process?

Answer 23

Screening

To remove large insoluble materials and grit

Question 24

What is produced during the sedimentation stage of sewage treatment?

Answer 24

Sewage sludge and effluent

Question 25

What occurs during anaerobic digestion in sewage treatment?

Answer 25

Bacteria digest sewage sludge in lack of oxygen to create natural gas and fertiliser

Question 26

What is the role of aerobic biological treatment in sewage treatment?

Answer 26

Aerobic bacteria remove organic waste from the effluent

Question 27

What is the final step in the sewage treatment process?

Answer 27

Sterilisation

The effluent is sterilised to remove harmful microbes using chlorine

Question 28

Define corrosion.

Answer 28

The destruction of material by chemical reactions in the environment

Question 29

What is rusting?

Answer 29

A type of corrosion of iron/steel when exposed to oxygen and water

Question 30

What are the conditions necessary for rusting to occur?

Answer 30

Both air and water need to be present and touching the metal

Question 31

How can corrosion be protected against?

Answer 31

By physical barriers

A coating applied to the metal, such as greasing, painting, or electroplating

Question 32

What happens if there are scratches in the protective barrier against corrosion?

Answer 32

Corrosion can happen

Question 33

What natural protection does aluminium have against corrosion?

Answer 33

An oxide coating formed by reacting with oxygen in the air

Question 34

What is a sacrificial barrier in corrosion prevention?

Answer 34

A coating of a more reactive metal that corrodes instead of the protected metal

Question 35

What is galvanizing?

Answer 35

Plating with zinc to protect against corrosion

Question 36

True or False: A sacrificial barrier must be applied only once.

Answer 36

False

It must be applied more than once as it can corrode away over time