Flashcards
C3.2 - Water Hardness
Cards in this deck (22)
- 1what does hard water form?scum
- 2what can soft water do easier than hard water?lather
- 3what can form when hard water is heated?limescale (CaCO3)
- 4how is scum formed?ions react with soap
- 5what ions cause hard water?Ca2+ and Mg2+
- 6what is Ca2+ good for in hard water?good for teeth and bones
- 7what is Mg2+ good for in hard water?reducing the risk of heart disease
- 8what is temporary hardness caused by?the hydrogen carbonate (HCO3-) ion in calcium hydrogencarbonate Ca(HCO3)2
- 9how can temporary hardness be removed?boiling
- 10what is the equation for temporary hardness?calcium hydrogencarbonate -> calcium carbonate + water + carbon dioxide
- 11what is permanent hardness caused by?dissolved calcium sulphate
- 12how can permanent hardness not be removed?by boiling
- 13how can permanent hardness be removed using washing soda?*adding sodium carbonate (Na2CO3)
*the CO32- ions react with the Ca2+ and Mg2+ ions in the hard water
*forms insoluble precipitate of calcium carbonate and magnesium carbonate which can be filtered out - 14how does an ion exchange column work?*sodium ions on resin beads
*exchange sodium ions for the calcium and magnesium ions
*adds the sodium ions to the water and takes out the calcium and magnesium - 15why is ok for the sodium ions to be in the water?doesn't make the water hard
- 16how can the ion exchange column be reused?running salt water through to replace the calcium and magnesium ions with the sodium ions
- 17how is water treated to be safe for drinking?*rainwater collected in reservoirs
*aluminium sulphate and calcium oxide added to remove dirt
*precipitate allowed to settle out
*water filtered through sand
*chlorine added to kill bacteria
*water quality tested before piped to customers - 18why does the use of chlorine have to be carefully controlled when killing microbes?it is toxic and can be used to make more toxic products
- 19why is fluoride compounds added to the water supplies and toothpaste?it prevents tooth decay
- 20what are one of the arguments against adding fluoride to water?people feel they should be able to choose if they have extra fluoride
- 21how is pure water made?distillation
- 22why is pure water not made very often?it needs a large amount of energy to boil so is expensive to produce on a large scale
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- GCSE Chemistry (C3) Flashcards on C3.2 - Water Hardness, created by Kelly Jowett on 12/05/2015.
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- Kelly Jowett
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