A huge pharmaceutical company is polluting the water supply of your town. How could you go about removing iron from the sample of ground water? 

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Iron is removed from municipal water supplies by a process known as oxidation.  Soluble iron ions in water are in the ferrous oxidation state (Fe2+).  When the iron is oxidized it is converted to the ferric oxidation state (Fe3+).  The ferric iron readily combines with hydroxide ions in the water...

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Iron is removed from municipal water supplies by a process known as oxidation.  Soluble iron ions in water are in the ferrous oxidation state (Fe2+).  When the iron is oxidized it is converted to the ferric oxidation state (Fe3+).  The ferric iron readily combines with hydroxide ions in the water to form iron hydroxide:

Fe3+ + 3(OH)- --> Fe(OH)3

Iron hydroxide is more commonly know as rust and it readily precipitates from water as a solid.  So you must add an oxidizing agent to the water to precipitate the iron from the water as rust and then simply filter off the solid.  The simplest and cheapest oxidizing agent is oxygen gas from the air.  Simply aerating the water by spraying it into the air or running it through the air as a waterfall will dissolve atmospheric oxygen into the water.  You can also bubble compressed oxygen into the water as well.  Another common oxidizing agent that is also used is chlorine.  This has the added benefit of killing harmful bacteria also present in the water.

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