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chemistry > water > Flashcards

water Flashcards

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1
Q

what happens when soft water and hard water mix with soap

A

the soft water lathers but the hard water doesn’t

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2
Q

what can natural water supplies contain

A

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

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3
Q

how can you save water

A

take shorter showers
fix leaky taps
reuse bath or sink water for washing plants

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4
Q

how can we abstract water

A

pumping water from underground
building dams and creating reservoirs
taking water from rivers and lakes
collecting rainwater
desalination

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5
Q

why is distribution of water hard

A

it’s expensive and most areas that need at the most are the poorest

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6
Q

what are the names of the 4 stages of purification of water

A

screening
sedimentation
filtration
chlorination

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7
Q

screening - stage 1

A

large objects such as leaves and rocks are removed by passing through a screen

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8
Q

sedimentation- stage 2

A

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

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9
Q

filtration stage 3

A

small objects are removed by passing the water through a fine sieve

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10
Q

chlorination stage 4

A

chlorine gas is bubbled and injected into water to sterilise it, chlorine is poisonous and kills the microorganisms

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11
Q

what is fluoridation

A

the addition of small amounts of fluoride to drinking water to prevent tooth decay

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12
Q

Advantages of fluoridation

A

fluoride on young children who have developing enamel makes it more resistant to acid attach
fluoride reduces ability of plaque forming

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13
Q

disadvantages of fluoridation

A

high concentrations of fluoride can cause fluorosis which stains teeth
it’s linked to bone cancer and infertility
mass medication- people have no choice

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14
Q

what is desalination

A

removal of salt from seawater to produce clean drinking water

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15
Q

micro filtration/ reverse osmosis desalination

A

seawater is forced through membrane at high pressure, membrane only allows water molecules

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16
Q

thermal desalination )distillation)

A

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

17
Q

why is desalination commonly used in the middle east

A

rainfall is low
countries have coastlines to access salty seawater
countries are wealthy

18
Q

Hard water

A

hard water contains dissolved magnesium ions and calcium ions after it comes into contact w limestone other rocks

19
Q

disadvantages of hard water

A

difficult to form lather with soap
scum forms
scale forms inside kettles, wasting energy
scale block pipes

20
Q

advantages of hard water

A

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

21
Q

temporary hardness removed

A

it’s removed by boiling the water, calcium hydrocarbonate decomposes

22
Q

permanent hardness

A

caused by dissolved calcium sulfate which can break down from boiling

23
Q

what the main ways of softening hard water

A

boiling
adding washing soda
ion exchange column

24
Q

method ad and dis of boiling temp hard water

A

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

25
Q

method, advantages and disadvantages of softening hard water by washing soda

A

adding washing soda (sodium carbonate) to hard water
calcium ions are removed so it’s not hard
advantages- works for temp and perm
disadvantage- limescale is formed

26
Q

how can we soften hard water by using an ion exchange column
advantages and disadvantages

A

used inside a dishwasher ion exchange removes hardness because the calcium ions stick to the column and get exchanged for sodium ions
water passes out of collin containing just sodium ions
advantages- works for temp and permanent hard water
disadvantages/ exchange columns are expensive and need to be regularly refreshed w sodium chloride

27
Q

how do we measure hardness experiment

A

put a known volume of water in a boiling tube
add soap solution one drop at a time and shake mixture for ten seconds
record number of drops needed to make a stable lather
to seperaye temporary and permanent hard water boil the samples
and repeat adding soap steps

28
Q

what happens if a substance is soluble

A

it will dissolve in a given amount of liquid called the solvent
when no more solute can dissolve the solution is said to be saturated

29
Q

how can we work out the solubility of a solid

A

measure some water and add to beaker
add small amounts of solute until no more can dissolve
record mass of evaporating fish
filter mixture so i dissolved solid is left behind and solution is in evaporating dish
remove water by heating or evaporation
weigh evaporating dish with solute in it
work out mass of solute that was dissolved

30
Q

what happens to solids as temperature increases

A

they become more soluble

31
Q

what does a solubility curve show

A

a graph that shows the solubility of a solute a different temperature

32
Q

what happens when you cool a saturated solution

A

results in crystallisation of some solute because solubility decreases w temperature

chemistry (5 decks)

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