Water

Water

1. Hard and Soft water

   • Hard water contains high concentrations of Magnesium and Calcium ions. It is formed in areas where water naturally flows of rocks containing these ions, such as calcium carbonate.
     • Calcium carbonate is not soluble however, so in order for it to dissolve into the water it reacts with the water and the co2 (that is also in the water) to form Calcium Hydrogen Carbonate (ca(HCO3)2) which is soluble.
     • Disadvantages of hard water include...
       • Hard water makes soap almost ineffective.
         • The magnesium and calcium reacts with the stearate ions in the soap to form a scum (insoluble), scum does not clean. Soap requires a lather to work and a lather only forms when all the mg and ca ions have been used. The hardness of a water can be measured by how much soap is needed before a lather forms. This makes hard water uneconomic to large business who need to use a lot of soap.
       • Hard water leaves deposits like scum and calcium carbonate called limescale, limescale reduces the efficiency of heating systems as they absorb the heat and limescale can also damage appliances.
     • Advantages of hard water include...
       • Calcium is good for bones and teeth.
       • Calcium has also been linked to a reduction in cardiovascular disorders.

2. Softening water

   • There are two types of hard water
     • Permanent hard water
       • Remains hard when boiled
         • Permanent hard water can be softened by adding washing soda, this contains sodium carbonate, the sodium is displaced by the magnesium and calcium to form insoluble magnesium and calcium precipitates. These can then be filtered out.
           • Another way of softening permanent hard water is using an ion exchange column, these contain a resin packed with sodium ions (which do not cause hardness) as the water goes through the column the calcium and magnesium are exchanged for sodium. The calcium and magnesium remain on the resin, this means it must be replaced.
     • Temporary hard water
       • Softens when boiled
         • Temporary hard water, is water that contains hydrogen calcium carbonate ions, these decompose into carbonate ions which react with the calcium and magnesium ions to create a precipitate, this can then be filtered out to leave soft water.

3. Purifying water

   • The process of treating water is as follows...
     • A fresh unpolluted source that does not contain high levels of dissolved salts should be located.
       • Water from this source should be sprayed onto layers of sand in a process called filtration. This should remove some of the larger impurities in the water such as dirt, rocks and litter.
         • Then a chemical is added to clump the finer particles together, these then sink to the bottom forming a segment which can be filtered out. This process is called sedimentation.
           • What is then chlorinated to kill the microbes in the water, this massively reduces the spread of waterborne diseases like cholera, however some people think it spoils the taste of water, and some research has be done that shows that when chlorine reacts with organic material, such as leaves, it forms THMs which can cause cancer.
             • Water is also fluoridated, this is very good for the teeth ands massively reduced serious dental incidences, However some people think that fluorine in water can reach toxic levels and it is being forced on the population. sea water needs to be distilled before it is drinkable, this is to remove the high level of dissolved salts, however this requires a lot of energy so countries which rely on the sea use renewable sources of energy.