Chemistry (C3) - The Water We Drink

This set is for AQA C3 Chemistry, GCSE, using the Nigel English books as a guide. This topic has four sub-topics:

Hard Water          Water Softening          Drinkable Water          Purify or Enhance?

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Hard Water

Hard Water is formed when group 2 ions dissolve into water. A common example is when rain water absorbs magnesium or calcium ions from the soil, making it hard.

Hard drinking water provides us with the calcium we need for our bones and teeth and reduces heart illness. It is prefered for making beer and some people say it tastes better.

However, hardwater reacts with soap to form scum which is an unsightly deposit on the bath or sink but more importantly, wastes soap which costs money. 

To overcome this problem, scientists have created soapless detergents that don't form scum. These are used in shampoos and washing up liquid.

The reason why we get scum is because one of the compunds is soap is sodium stearate, which is soluble in water, and it reacts with the calcium or magnesium ions in hard water to form insoluble calcium or magnesium stearate (insouluble).

hard water is tested for by adding salt solution, if the water is hard, scum is formed once shaken, if the water is soft, lather forms immediately. 

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Water Softening - Problems of Hard Water

All rain is slightly acidic because carbon dioxide dissolves in water to form a weak solution of carbonic acid.

The acidic rain then falls on rocks to set off slow chemical reactions called chemical whethering. However, on rocks made of calcium carbonate, such as limestone, the rocks dissolve away as soluble calcium hydrogencarbonate. 

As hard water evapourates, some carbon dioxide is lost with the water to allow calcium carbonate to reform. this process is then enhanced if the water is heated and that is why we get unsightly limescale on kettles or pipes.

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Water Softening - Prevention

Hard water containing hydrogencarbonate ions is only temporary hardness because the ions can be removed by boiling the hard water. However, this has no effect on hard water with calcium or sodium ions, that is called permanent hardness.

To get rid of scum in the bath, you should add bath salts as this softens the water. This is because the calcium ions swap with sodium ions which do not  react with soap to form limescale, however, this method does not work for pipes or central heating systems.

The method for pipes of central heating is to by an expensive water softener. this contains sodium or hydrogen ions and swaps them with the magnesium or sodium ions. These can run for long times. Unfortunately, the sodium ions coming out are not good for our health and can lead to high blood pressure or heart problems, therefore, no water should be drunk from the water softener.

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Drinkable Water

In Britain, drinking water is collected from rainfall and in drier places, wells are built to get drinking water. However, before it is drunk it will need treatment.

Filter beds are used which, with every filter, remove smaller and smaller solids. However, this is still not fit to drink as it still may contain harmful microoorganisms, these can be removed by adding a controlled amount of chlorine, after this, the water is clean to drink.

The water that comes out of our taps are still not pur and contain harmless dissolved salts.

Some prefer to drink mineral water because they think it is safer or the prefer the taste. 

An alternative to buying bottled mineral water is to have a home filtering system which use activated carbon and / or microscopic silver.

Activated carbon is crushed charcoal, given a positive charge to attract containments, the charcoal has to be replaced on a regular basis.

Silver is used as porous ceramic fitlers impregnated with microscopic particles of silver which kill any microorganisms which otherwise may have grown on the filter. 

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Purify or Enhance?

Only 3% of water is fit to drink and 1% is not locked up in glaciers. 

Distillation is used to purify sea water on a still as it evapourates, water condenses elsewhere leaving the salts and impurities behind. In a solar still, the energy to evapourate the water is prvided by the sun. They are commonly found in desert coastlines.

Energy can also be provided by fossil fuels but this is very expensive and does not use a renewable source. It also produces concerntrated salt water which could damage an ecology of the sea if not disposed with care.

Hard water has, however, been proven to be better for you than pure water as it strengthens your teeth and bones, increases overall life span and reduces the risk of heart problems, some intestinal cancers and lead poisoning.

After it was discovered that people living with a higher concerntration of flourine ions in their water, debates have raged on whether to add flourine to all drinking water as some people say is weakens bones and mottles teeth, also people question whether it is fair to force people to have flourine in their water whether the want it or not.

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