C4 Purifying and testing water

Water has domestic uses, such as: drinking and washing, as well as industrial uses like. This is an ideal material for the industries to use because:

• It is a cheap raw material
• It can be used as a coolant
• It can be used as a solvent

It is important to conserve water because, the amout of fresh water on earth is very limited.If water is over used (especially in dry weather) there may be water shortages and hosepipe bans. Conserving water also saves the material a that is used to transport and treat.Some examples of sources of water are:

• Lakes 
• Rivers
• Aquifiers- An underground layer of permeable rock, gravel and sand that is soaked in water.
• Reservoirs- A lake that is made by building a dam, to save and accumulate water in the valley behind

Water has domestic uses, such as: drinking and washing, as well as industrial uses like. This is an ideal material for the industries to use because:

• It is a cheap raw material
• It can be used as a coolant
• It can be used as a solvent

It is important to conserve water because, the amout of fresh water on earth is very limited.If water is over used (especially in dry weather) there may be water shortages and hosepipe bans. Conserving water also saves the material a that is used to transport and treat.Some examples of sources of water are:

• Lakes 
• Rivers
• Aquifiers- An underground layer of permeable rock, gravel and sand that is soaked in water.
• Reservoirs- A lake that is made by building a dam, to save and accumulate water in the valley behind

Water pollutants:

• Nitrate fertilisers are very soluble in water and are easily washed off fields by the rain and then into rivers and reservoirs. Because nitrates are all soluble they cannot easily be removed from the water.
• Older houses and water supply systems still rely on lead pipes. Poisonous lead compounds formed on the inside of the pipes slowly dissolve into the water.
• Pesticides used by farmers to kill weeds or insects may be washed or blown into streams and rivers.

Raw water consists of :

• Dissolved salt
• Dissolved minerals
• Microbes
• Pollutants
• Insoluable materials, e.g sand and stones

The order in which water is purified:

1) Filteration- The water is sprayed onto specially prepared layers of sand and gravel. As it trickles through, different sized insoluble solids are removed. The filter beds are cleaned periodically by pumping clean water backwards through the filter.

2) Sedimentation- A chemical is added which causes tiny solid particles (which would pass through a filter) to clump together into larger particles. These can then be allowed to settle out or may be filtered.

3) Chlorination- Chlorine gas, injected into the water, kills microbes.

Persipitate reactions are ways of testing various ions, or particles in water. Here are some examples:

• Testing of sulfate ions. Barium Chloride is added to a sample of water that is to be tested. If sulfate ions are present, Barium Sulfate will be formed, to create a white persipitate, as it is insoluable in water.

Barium Chloride(aq) + Sodium Sulfate(aq) = Sodium Chloride(aq) + Barium Sulfate (s)

• Testing for Halides (halogens from group 7). Silver Nitrate is added to a sample of water that is to be tested. If halide ions (iodide, chloride, bromide) are present, Silver Halide will be formed to create a persipitate. They will formed as shown below: Silver Chorlide forms white persipitate, Silver Bromine forms cream persipitate, Silver Iodide forms pale yellow percipitate.

An example reaction:

Silver Nitrate(aq) + Sodium Bromide(aq) = Sodium Nitrate (aq) + Silver Bromide (s)

Some soluable substances cannot be removed from water during the purification process, such as nitrate fertilisers. This is usually washed down from the farmland, into rivers and lakes. Nitrates can be poisonous (especially to young people and in high concentration). Thus, the water must be treated with care to make sure that the nitrate concentration is very low.

Distillation of sea water

A process where large volumes of fresh water can be made from sea water, which uses a lot of heat energy to boil. Thus, the fresh water derived from distillation could be more expensive, than the water from traditional sources. Also, disposal of the large quantities of the waste products, such as salts. Howbeit, this process is still used in hot countries, such as Saudi Arabia.