Using resources - Chemistry Paper 2 Flashcards
What is potable water?
Water that is safe to drink
Why isn’t potable water pure?
Because it contains other dissolved substances too - not just water
What is the pH of potable water?
between 6.5 and 7.5
Where does most potable water in the Uk come from?
Fresh water sources e.g lakes, rivers, reservoirs, aquifers
What are aquifers?
Rocks that trap water underground
What are the processes of treating fresh water?
Filtration which involves passing the water through filter beds to remove insoluble particles. And, sterilisation, which involves killing harmful bacteria or microbes in the water
How is fresh water sterilised?
Using chlorine, ozone, or ultraviolet light
How can desalination be performed?
Through distillation or through reverse osmosis
What happens during the reverse osmosis of sea water?
Salty water is passed through a membrane that only allows water molecules through. Ions and larger molecules , like salt, are trapped by the membrane and so are separated from the water.
How does distillation remove salt from seawater?
Sea water is heated until it boils. The salt remains in the liquid, and the steam is pure water. The steam is cooled and condensed to make potable water.
What are the disadvantages of desalination methods?
They require a lot of energy and are very expensive. Reverse osmosis also produces a large volume of waste water, so its efficiency is often quite low.
Why does waste water need to be treated?
- human waste contains harmful bacteria and high levels of nitrogen compounds which can harm aquatic ecosystems
- industrial waste water may contain harmful chemicals such as toxic metal compounds
- agricultural waste water may contain fertilisers or pesticides which can disrupt sensitive ecosystems
What are the stages of waste water treatment?
Screening
Sedimentation
Aerobic digestion of effluent
Anaerobic digestion of sludge
What happens during the screening stage of waste water treatment?
Insoluble and large objects are removed, like sticks
What happens during the sedimentation stage of waste water treatment?
In a settlement tank, the heavier suspended solids sink to the bottom to produce sludge and the less dense effluent floats to the top
What happens during the aerobic digestion stage of waste water treatment?
The effluent is treated via aerobic digestion. This is where air is pumped through the water to encourage aerobic bacteria to break down any organic matter - including other harmful microbes in the water
What happens during the anaerobic digestion stage of waste water treatment?
The sludge gets broken down by bacteria via anaerobic digestion. The organic matter in the sludge is broken down, releasing methane gas and digested waste
What can the methane gas from waste water treatment be used for?
As an energy source
What can the remaining digested waste from waste water treatment be used for?
Fertilisers
What is effluent treated with?
chlorine, ozone and ultraviolet light
What is the Haber process?
when nitrogen gas is reacted with hydrogen gas to make ammonia gas. The forward reaction is exothermic.
What is the word equation for the Haber process?
nitrogen + hydrogen <=> ammonia
What is the symbol equation for the Haber process?
N2 + 3H2 <=> 2NH3
Where does the nitrogen for the haber process come from?
The air
