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Chemistry unit 3 revision

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Hard Water and Soft Water

Natural Water contains Microorganisms and dissolved salts to produce quality water we do this. Pass the water through a filter bed to remove any solid particles. Chlorine gas is then added to kill any microorganisms. Water can be then passed through a filter which gets rid of any left over compounds (optional).

Any water can be distilled to produce by boiling it then catching the condensed air.

The amount of compounds present in water determines whether it is Hard Water or Soft Water. Soft water doesnt contain many dissolved substances making it easily latherable with soap, where as hard water contains magneisium and calcium compounds which react with soap to form scum, making it not very latherable. The magnesium and calcium come from rocks and the ground.

Hard Water is good for your body as calcium helps with the development of strong bones and teeth, calcium also reduces the risk of getting heart disease.

Mort soap is needed to form a lather when washing, which increases the overall costs of living, furthermore hard water can lead to limescale which forms in different appliances, reducing the efficiency of the appliance.


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Hard Water being Removed.

To get rid of the Hardness in hard water you can add sodium carbonate solution which causes the carbonate ions to react with the magnesium and calcium which forms Magnesium carbonate and calcium carbonate which both percipate out of the solution as they both become insoluble.

You can also get rid of the hardness by passing the hard water through a Ion - exchange column which contains a resin that provides hydrogen and sodium ions which swap with the magnesisum and calcium compounds for the hydrogen and sodium ions when the water passes through the filter.

Key Facts:

  • Magnesium carbonate & Calcium Carbonate both percipate out the solution when they have reacted with Sodium carbonate solution because they both become insoluble.
  • Sodium and hydrogen ions swap with the manesium and calcium compounds when the hard water passes through the water filter.
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Identifying Substances

Flame tests - Flame tests can be used to idenify Metal Ions. Different metal ions produce different colours when in the presence of a flame. This is called a flame test. From doing this we can identify which metal ion is present, To do this we dip a Nickel-chromium alloy in some hydrochloric acid to clean it. We then dip the alloy in the comound followed by the flame.

These colours repesent the metal ion:

  • Apple Green for Barium
  • Brick Red for Calcium
  • Red for lithium
  • Lilac for Potassium
  • Yellow for Sodium

Reacting Carbonates with Dilute Acid - Carbonates reach with dilute Acids to form Carbon dioxide (gas), a salt and then some water. Carbon dioxide turns lime water milky.

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Identifying Substances

Precipitation Of Metal Ions - Metal compounds in solution contain metal ions. Some of these form preciptates, which are insoluble solids that come out of solution when sodium hydroxide solution is added to them.

For example, when sodium hydroxide solution is added to calcium chloride solution, a white precipate of calcium hydroxide of calcium hydroxide is formed.(as well as sodium chloride solution).


  • Decomposition
  • Insoluble
  • Ion
  • Precipitate
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Former Member



Amber Hornsby


Hello water revision ;)

Michael Gunson


Perfectly okay, you see i am expecting A* over in chemistry and just thought i would do the honourable thing and supply the world with the knowledge which i have quite clearly excelled through. :D

Amber Hornsby


Paha, loser.

My water notes are ace ;)and specially colour coded

Spell check it too :)

Alice Manterfield


sad people ;)

not that I can talk with my profile picture ^^


Amber Hornsby


Shussshhh alice :)

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