Chemistry - 14 The Earth's Resources - 14.1 Finite and Renewable Resources & 14.2 Water Safe to Drink & 14.3 Treating Waste Water

Renewable

resources that will not run out and reform as they are used

Finite

resources that will run out and cannot reform at the same rate as they are used

Natural resources [5]

- wood

- rubber

- fossil fuels

- metal

- water

Man-made resources [4]

- plastic

- glass

- paper

- alloys

Sustainable development

development that meets the needs of the present without compromising the needs of the future

Biofuels

fuel derived directly from living matter

Ore

rock that contains enough metal to make it economically worth extracting

Advantages of mining [2]

- creates employment opportunities

- brings money to local and country economy

Disadvantages of mining [4]

- metals are finite

- noise and dust pollution from machines

- greenhouse gases from machinery

- damages habitats and settlements

How can ethanol be made? [2]

- fermentation of glucose

- cracking of ethene

What features define a 'good' fuel? [4]

- strongly exothermic

- easy to make/extract

- non-toxic (including products)

- cheap

Advantages of fermentation to produce ethanol [3]

- sugar cane regrows (renewable)

- sugar cane absorbs carbon dioxide as it grows

- low energy process

Disadvantages of fermentation to produce ethanol [3]

- ethanol produced is impure

- large areas of land required

- slow process

Advantages of cracking ethene to produce ethanol [2]

- pure product

- faster process

Disadvantages of cracking ethene to produce ethanol [2]

- high energy process (requires high temperatures)

- uses finite resources

Potable

suitable and safe to drink

Groundwater

water held underground in the soil or in pores and crevices in rock

Surface water

water that collects on the surface of the ground, such as in rivers and lakes

Fresh water

water that contains insignificant amounts of salts, as in rivers and lakes, from rain

Sterilising agent

removes microorganisms from an object or substance

Sterilising agents used to treat drinking water [3]

- chlorine

- ozone

- UV light

Treating fresh water process [6]

- water travels through screens to filter out debris

- settlement tank allows sand and soil to settle out

- aluminium sulfate and lime are added to cause particulates to clump and sink

- passed through a filter made from fine sand and gravel

- sterilising agents are added to kill pathogens

- potable water is kept in a reservoir

Pure water

only contains H₂O molecules

Pure water is made by ...

distillation

Why is drinking water not distilled? [4]

- time-consuming

- high energy process

- expensive

- unnecessary

Why might desalination be needed? [2]

- surface water evaporates in hotter areas

- drier regions may not get enough rain for their population

How is an appropriate source for potable water found? [2]

- samples are evaporated and crystallised

- solids are weighed and compared to total mass

Desalination

removing salt from water

Methods for desalination [2]

- distillation

- reverse osmosis

Flash distillation

reducing pressure so that water's boiling point becomes lower, which saves on energy and money

Reverse osmosis

water is pressurised through a partially permeable membrane, removing 98% of salts

Problem with reverse osmosis

requires high energy and money

Sewage

solid and liquid waste from homes, businesses and agriculture that is carried away by sewers or drains

What must be removed from sewage? [3]

- organic matter

- harmful live microbes

- harmful chemicals

Treatment of sewage [4]

- screening

- primary treatment

- secondary treatment

- final treatment

Screening

passing sewage through mesh screens to remove solid debris

Primary treatment [2]

- sedimentation

- separation of sludge and effluent

Sedimentation

allowing solid substances to settle out of the sewage

Sludge

solids from sewage

Effluent

sewage without solid debris

Secondary treatment [1]

- aerobic digestion of effluent

What is the purpose of aerobically digesting effluent?

breaking down any remaining organic matter, including harmful microbes

Final treatment [3]

- secondary sedimentation

- (optional) filtering

- (optional) sterilisation

Secondary sedimentation

allows remaining organic matter, including both harmful and helpful microbes, to settle out

Sludge treatment [2]

- anaerobic digestion

- drying out

Anaerobic digestion of sludge [2]

- can take up to 30 days

- releases biogas which can be used as fuel

Drying sludge

can be dried into 'cakes' which can be burnt to generate electricity