goodbye forever chemistry!!!!!!!!!!! Flashcards
(47 cards)
Potable water what is it
safe to drink
3 conditions for potable water
-low levels of dissolved substances
-ph 6.5-8.5
-no microorganisms
where do you get potable warter - limitations of surface warer
-fresh water e.g. rain collects as surface (e.g. lake/river) /ground (e.g. aquifer) water
surface water benefit - easy access, replaced by rain
but can dry if hot and sunny
OR
-de salination
how is fresh water treated? 3 steps
- pass through wire mesh - filter big things out
- pass through bed of sand and gravel - filter smaller solids
- sterilise - kill harmful microbes
-bubble chlorine gas
-expose to ozone
-expose to UV
Desalination problems
requires loads of energy and expensive
How is water desalinated by simple distillation?
water vapour collected and condensed
How is water desalinated by reverse osmosis?
passed through membrane - only allow water through
-ions and larger molecules trapped and separated
3 main sources of waste water
- domestic - household e.g. showers, sinks, toilets - sewers, sewage treatment plants
- Agriculture - nutrient run off - animal waste
- Industrial - factories that make and use chemicals
What must be done to waste water before disposal?
treatment to make it safe
How is domestic and agricultural waste water treated to make it safe
Remove any organic matter and harmful microbes which could pollute fresh water and make people ill.
How is industrial waste water treated to make it safe
Extra steps needed to remove harmful waste chemicals
How does sewage treatment work? - 3 general steps
- screening - pass through mesh, anything large filtered out
- let sewage sit in settlement tank - undergo sedimentation - heavy solids sink to form sludge, lighter effluent part left at top
then separate into 2 tanks - sludge and effluent - breakdown of organic matter - biological breakdown by microorganisms - effluent - aerobic - pump air in
sludge - anaerobic - tank sealed
so microbes break down organic matter in effluent tank by aerobic digestion but organic matter in sludge - anaerobic
eventually, effluent water is safe and can be released back into the envuironment.
sludge - anaerobic produces methane - captured and burned as energy source. remaining digested waste used as fertiliser as its rich in nutrients
What additional stages remove toxic substances
- adding chemicals
- UV radiation
Why do some countries rely on waste water for their drinking supplies?
Much cheaper than desalination
What is haber process
industrial preoduction of ammonia from nitrogen and hydrogen
what is the ammonia from haber process used for?
nitrogen based fertilisers - allow us to grow enough food.
How we aquire nitrogen and hydrogwen for haber process
nitrogen - in air
hydrogen - make it from hydrocarbons
Is the haber process reaction exothermic, reversible or both?
both
How does the Haber Process work?
- nitrogen and hydrogen fed into top left of machine, where they mix
- in the reaction vessel, conditions are kept at 450 degrees C and 200 atmoapheres pressure
- gases free to pass over iron catalyst
- under the conditions in the reaction vessel, some of the nitrogen and hydrogen will react to form ammonia but as the reaction is reversible, there will still be nitrogen and hydrogen too.
- to separate ammonia, pass entire mixture through pipe into condenser (much cooler)
- ammonia has a low b.p.t so condenses whilst hydrogen and nitrogen stay gaseous and are recycled back to the reactant mixture
Why 450 deg and 200 atm for haber
temp:
exothermic so need low temp to favour forward for high percentage yield.
but need high temp for higher rate of reaction as particles need enough kinetic energy to react
450 deg is a compromise
higher temp also too costly
pressure - high pressure for high percentage yield as fewer molecules of gaseous product than reactant and high pressure shifts equilibrium to the left.
high pressure - more frequent collisions so higher rate of reaction
so oly thing limiting how hogh pressure is are cost and safety
maintaining high pressure is expensive and dangerous if something goes wrong
200 atm is a compromise - best overall
what is a fertiliser?
a substance that is applied to soil, in order to supply plants with nutrients.
How are fertilisers made - past, now
In the past, fertilisers were usually made from animal waste such as cow manure. Now though, we tend to use formulated fertilisers, which are made in factories.
what is a formulated fertiliser
A formulation is a mixture that has been designed as a useful product. So if we make fertilisers by combining certain chemicals in a specific ratio, then we would call it a formulated fertiliser.
3 key parts of formulated fertilisers
The three main elements that plants needs from the soil are are nitrogen (N), phosphorus (P), and potassium (K). For this reason, fertilisers normally consist mainly of nitrogen, phosphorus, and potassium compounds.
This is why we sometimes call them NPK fertilisers. NPK fertilisers are formulations of various salts containing appropriate percentages of these three elements.
