Air and water Flashcards
What is the evidence for the composition of the early atmosphere?
Very limited evidence due to its occurrence about 4.6 billion years ago.
How did the early atmosphere likely compare to the atmospheres of Mars or Venus?
It consisted mostly of carbon dioxide with little or no oxygen gas and nitrogen.
What role did volcanic activity play in the formation of the early atmosphere?
Released mainly carbon dioxide and water vapour, gradually producing nitrogen.
What small proportions of gases may have been present in the early atmosphere?
- Methane
- Ammonia
How were the oceans formed?
From temperatures cooling, causing water vapour to condense into water.
What process led to the decrease of carbon dioxide in the atmosphere?
Carbon dissolved in water, forming carbonates that produced sediments.
When did photosynthetic organisms first begin to produce oxygen?
About 2.7 billion years ago.
What is the equation for photosynthesis?
6CO2 + 6H2O → C6H12O6 + 6O2
How did photosynthesis contribute to the atmosphere’s oxygen levels?
Produced oxygen and decreased carbon dioxide.
What are two additional ways carbon dioxide levels were decreased in the atmosphere?
- Formation of sedimentary rocks
- Formation of fossil fuels
What has been the proportion of gases in the atmosphere for the past 200 million years?
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.
What is potable water?
Water that is safe to drink
Potable water needs to have sufficiently low levels of dissolved salts and microbes.
Is potable water pure water in the chemical sense?
No
Potable water contains dissolved substances.
What provides fresh water in the UK?
Rain
Rain provides water with low levels of dissolved substances that collects in the ground and in lakes and rivers.
What is the first step in making fresh water safe to drink?
Passing it through filter beds
This typically includes a wire mesh followed by a bed of sand or gravel.
What is the purpose of sterilisation in water treatment?
To kill the microbes in the water
Sterilising agents can include chlorine, ozone, or ultraviolet light.
What may be required if there are limited supplies of fresh water?
Desalinisation of salty or sea water
Desalinisation can be done by distillation or reverse osmosis.
How is reverse osmosis performed?
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.
What are the energy requirements of desalinisation processes?
They require large amounts of energy
Filtration and sterilisation may also still be needed after these processes.
What types of waste require treatment before being released into the environment?
Sewage and agricultural waste water
Treatment is necessary due to organic matter and harmful microbes.
What needs to be removed from sewage and agricultural waste water?
Organic matter and harmful microbes
This is crucial for environmental safety.
What is required for the treatment of industrial waste water?
Removal of organic matter and harmful chemicals
What is the first step in the sewage treatment process?
Screening
To remove large insoluble materials and grit
What is produced during the sedimentation stage of sewage treatment?
Sewage sludge and effluent
What occurs during anaerobic digestion in sewage treatment?
Bacteria digest sewage sludge in lack of oxygen to create natural gas and fertiliser
What is the role of aerobic biological treatment in sewage treatment?
Aerobic bacteria remove organic waste from the effluent
What is the final step in the sewage treatment process?
Sterilisation
The effluent is sterilised to remove harmful microbes using chlorine
Define corrosion.
The destruction of material by chemical reactions in the environment
What is rusting?
A type of corrosion of iron/steel when exposed to oxygen and water
What are the conditions necessary for rusting to occur?
Both air and water need to be present and touching the metal
How can corrosion be protected against?
By physical barriers
A coating applied to the metal, such as greasing, painting, or electroplating
What happens if there are scratches in the protective barrier against corrosion?
Corrosion can happen
What natural protection does aluminium have against corrosion?
An oxide coating formed by reacting with oxygen in the air
What is a sacrificial barrier in corrosion prevention?
A coating of a more reactive metal that corrodes instead of the protected metal
What is galvanizing?
Plating with zinc to protect against corrosion
True or False: A sacrificial barrier must be applied only once.
False
It must be applied more than once as it can corrode away over time
