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sonyalo
Temporary Hardness testing

I was doing 2018 question one and the last question was to suggest a way of detemining if the water supply contained temporary hardness. Initially I thought that you coould use the anion test for the hydrogencarbonate where upon addition of magnesium sulfate and Heat a precipitate forms. Since temorary hardness is caused my calcium hydrogencarbonate But the answers in the marking scheme where to boil the water; titration ; amount of lather formed. Just wondering if that makes sence....


2 Comments
MRREILLY
MRREILLY
The problem with your answer is that hardness is caused by Calcium or Magnesium ions whereas you are testing for the hydrogen carbonate ion which can occur in water without either of Ca2+ of Mg2+ being present. Therefore to boil the water and look for the limescale precipitate or titrate against EDTA would be your best bet
Fergal
Fergal
The good old Junior Cert method was to test a 10cm3 sample of hard water with LUX soap flakes and count the number of flakes needed to give a lather (say 7). Then boil the water and test another 10cm3 of the water with LUX flakes. If all hardness is temp then just one flake of soap will give some lather. If some permanent hardness remains after boiling then 3-4 flakes wil be required to get a lather.
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