water Flashcards
what happens when soft water and hard water mix with soap
the soft water lathers but the hard water doesn’t
what can natural water supplies contain
dissolved ions
picks up sodium calcium magnesium ions as it runs through rocks
dissolved gases
gases from the atmosphere dissolve into the water as it falls as rain oxygen carbon dioxide
microorganisms
bacteria from animal waste can lead to diseases
pollutants
chemical fertiliser and pesticides can be washed into rivers at a toxic level
how can you save water
take shorter showers
fix leaky taps
reuse bath or sink water for washing plants
how can we abstract water
pumping water from underground
building dams and creating reservoirs
taking water from rivers and lakes
collecting rainwater
desalination
why is distribution of water hard
it’s expensive and most areas that need at the most are the poorest
what are the names of the 4 stages of purification of water
screening
sedimentation
filtration
chlorination
screening - stage 1
large objects such as leaves and rocks are removed by passing through a screen
sedimentation- stage 2
sedimentation- aluminium sulfate is added to water causing particles to clump and sink to the bottom of tank or reservoir, cleaner water can be extracted from the top
filtration stage 3
small objects are removed by passing the water through a fine sieve
chlorination stage 4
chlorine gas is bubbled and injected into water to sterilise it, chlorine is poisonous and kills the microorganisms
what is fluoridation
the addition of small amounts of fluoride to drinking water to prevent tooth decay
Advantages of fluoridation
fluoride on young children who have developing enamel makes it more resistant to acid attach
fluoride reduces ability of plaque forming
disadvantages of fluoridation
high concentrations of fluoride can cause fluorosis which stains teeth
it’s linked to bone cancer and infertility
mass medication- people have no choice
what is desalination
removal of salt from seawater to produce clean drinking water
micro filtration/ reverse osmosis desalination
seawater is forced through membrane at high pressure, membrane only allows water molecules
thermal desalination )distillation)
salty water is placed in flask and heated until it becomes steam,
steam rises into liebig condenser
cold jacket of water enters condenser where it cools and turns water back into liquid
water is collected in a beaker and the salt is left behind in flask
why is desalination commonly used in the middle east
rainfall is low
countries have coastlines to access salty seawater
countries are wealthy
Hard water
hard water contains dissolved magnesium ions and calcium ions after it comes into contact w limestone other rocks
disadvantages of hard water
difficult to form lather with soap
scum forms
scale forms inside kettles, wasting energy
scale block pipes
advantages of hard water
some people prefer the taste
calcium in it is good for children’s teeth and bones
scale stops poisonous salts from dissolving in our water
temporary hardness removed
it’s removed by boiling the water, calcium hydrocarbonate decomposes
permanent hardness
caused by dissolved calcium sulfate which can break down from boiling
what the main ways of softening hard water
boiling
adding washing soda
ion exchange column
method ad and dis of boiling temp hard water
method- heated to boil to become soft
layer of lime scale forms at bottom
advantages- easily done and not expensive
disadvantages- only works for temp hardness and only practical for small volumes of water
