Water summary

Here is a water summary for everything you need to know about for AQA triple award chemistry

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The water cycle
This is where the heat from the sun causes the evaporation of water from the salt solution (the sea) and the
water vapour is then carried upwards because warm air rises and as the air rises it cools due to general
cooling of the lower part of the atmosphere at higher altitudes. This makes the temperature fall and so the
water condenses to forms clouds and then precipitation occurs as condensed droplets get too heavy and
fall. The water then runs back into the sea however, on the water's journey back to the sea at some stage
the water comes into contact with the rocks on/or underneath the ground. This means that the water in
different places will dissolve different materials.
Where else could water vapour occur?
Water vapour could occur from evaporation, transpiration, respiration and the combustion of fossil fuels.
How can water be polluted and how can you treat it?
Water can be polluted by: fertilising leaks, dumped waste and sewage leaks.
The process of water treatment drinking water has to be treated in order to make it safe. Solids are
removed in large filter beds then chlorine is added to kill any bacteria present. Other treatments may also be
used depending on the purity of the water source.
What is `hard' water?
Hard water is where there is a presence of Ca2+ and/or Mg2+ ions.
Hard water can be tested by titration. This is with the use of a soap solution and a known value of water and
if it lathers easy in the time given then it is soft water because less soap is needed so in hard water more
soap is needed in order to form lather.
Advantages Disadvantages
Hard water Good for your health as Calcium ions Washing becomes more
are needed to produce healthy bones expensive due to the soap
and teeth. reacting with Calcium ions and
this forms a greasy scum and
this sticks to clothes and to stop
this reaction extra soap is
needed to form lather and
causes the buildup of lime
scale in kettles.
Soft water Contains few or no Calcium and They are less health benefits.
Magnesium ions.
What are the different types of hardness?
Hardness is caused by calcium hydrogencarbonate and can easily be removed through heating.
Permanent hardness is caused by calcium sulphate and cannot be removed through heating.
Soap stearate is added with Mg2+/Ca2+ to form magnesium/calcium stearate.

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This is Calcium Carbonate (lime scale).
How did the ions come in contact with the water to form hard water?
Water has passed over (contact) over rocks that contained Calcium/Magnesium ions. Water has reacted
with the rocks and minerals dissolve in the water to form the hard water.
If there is a comparison question then compare and include both points and use words such as `harder'
`softer' `stronger'.…read more


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