Hard and Soft Water

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  • Created by: Hope
  • Created on: 06-05-14 19:20

Hard Water

Hard water makes scum and scale. 

Hard water doesnt lather easily with soap and you get scum instead. The problem is the 'hardness minerals' in the water reacting with the soap.

Hard water also forms scale (which is mostly calcium carbonate) on the insides of pipes boilers and kettles - which reduces the efficency - as scale is a thermal insulator so things (e.g. kettles) will take longer to boil. 

Hardness is caused by....

Because it contains lots of calcium and magnesium ions.

You get hard water in certain areas because of the type of rocks there. Hardness comes from - limestone, chalk and gypsum.

When carbon diocide from the air dissolves in rain water, uoi get carbonic acid - so rain water is slightly acidic.  So if theyres calcium carbon ate in the rocks calcium hydrogencarbonate is formed which is soluable.

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Hard Water 2

  • Ca2+ ions are good for healthy teeth and bones (so it isnt all bad)
  • Scale inside pipes forms a protective coating 
  • Can improve the taste of water 

A way of testing how hard water is, is to carry on titration - the harder the water, the greater volume of soap solution needed.

Types of hardness

Temporary hard water can be softened when it is boiled

Permenant hard water stays hard, even when boiled. 

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Softening Hard Water

The two methods of softening hard water are...

  • Ion exchange column 
  • Adding sodium carbonate to the water

Adding sodium carbonate:

  • 'Washing soda'
  • Can remove temporary and permenant hardness from water
  • The carbonate ions from the sodium carbonate react with the calcium and magnesium ions to make an insoluable precipitate
  • This insoluable precipitate becomes limescale - which causes things to clog up and break

Ion Exchange Columns

  • Use ion exchange resin beads
  • Resin beads have sodium ions attactched to them
  • When hard water runs through the sodium ions swap places with the magnesium and calcium ions so the water is less hard and contains more sodium ions
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Supplying safe water

Water can be found in lakes, rivers, aquifers and reseviours 

You must filter the water to make sure it is safe to drink, they do this with different filter beds. They then chlorinate the water to sterilise it and stop any harmful microbes getting into our bodies

Adding flouride to the water supply;

Flouridated water can improve dental health, some communities make water suppliers add extra flouride to the water.

Filtering water at home:

Water from taps is safe to drink but it not pure because it contains dissolved mineral ions and chlorine. Filtering removes impurities and helps to soften the water. 

We can also obtain water from the sea but we have to distill it which is expensive and bad for the environment. Purity of water can be tested by; its boiling point and evaporating it. Boiling points increase as the concentration of salts increase. Pure water will leave no solids after evap

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