Water Flashcards
What is soft water?
Water that lather easily with soap
What is hard water?
Water that uses lots of soap to produce a lather and wash effectively.
What insoluble compound is formed when hard water reacts with soap and why?
Hard water contains compounds dissolved in it that react with soap to form the insoluble solid, called scum.
What two ions are found in hard water?
Calcium and magnesium ions
How can temporary hard water be softened and what solid is formed in this process?
Temporary hard water is softened by boiling as the calcium and magnesium ions form insoluble scale and this removes them from the water.
What problems can scale cause if deposited in kettles, boilers and pipes?
It causes blockages and reduces the efficiency of heating systems.
In what ways are calcium compounds good for health?
They help to develop strong bones and teeth and they may also reduce the risk of heart disease.
What does temporary hard water contain and how does this make it possible to soften temporary hard water by heating?
Temporary hard water contains hydrogencarbonate ions, which decompose when heated to produce carbonate ions, water and carbon dioxide.
The carbonate ions react with calcium and magnesium ions in water to produce precipitates of calcium carbonate and magnesium carbonate that are deposited as scale.
How can washing soda be used to soften either type of hard water?
Washing soda, sodium carbonate can be added to hard water, the sodium carbonate reacts with the calcium and magnesium ions in the water to from solid calcium carbonate and magnesium carbonate that cannot react with soap.
How can an ion-exchange column be used to soften either type of hard water?
An ion-exchange column is packed with a resin containing sodium or hydrogen ions.
Hard water is passed through the column.
The sodium or hydrogen ions from the resin are exchanged with calcium and magnesium ions in hard water.
the calcium and magnesium ions become attached to the resin.
Sodium and hydrogen ions in the water do not react with soap.
How can the resin in an ion-exchange column be replenished with sodium ions?
The resin can be washed with a solution of sodium chloride, which will replenish sodium ions in the resin.
This is why water softeners must be kept topped up with salt.
Outline the different stages and processes involved in water treatment.
1) The water is passed through a special filter made of fine sand to remove any remaining mud or grit.
2) The water is passed through a metal grid, which filters out large objects such as leaves and twigs.
3) The water then enters a settlement tank, where sand and soil settle out.
4) Aluminium sulfate and lime are added to the water, small particles of dirt clump together so that they sink to the bottom of the water, the sludge that collects is then removed and dumped in a landfill site.
5) A small amount of chlorine is added to the water to remove harmful bacteria.
6) pH of water is now checked to make sure it is neutral.
Why is fluoride added to drinking water in some areas?
Fluoride helps to prevent tooth decay
How can we purify water? What would be the problem with this process on a large scale?
Water can be purified by distillation, however this requires large amounts of energy to boil the water and so would be expensive on a large scale.
Give advantages and disadvantages of adding chlorine to water supplies.
Advantages:
Kills harmful bacteria in water so that it is safe to drink
Can be used to treat sewage before it is returned to rivers or the sea
Disadvantages
Chlorine can react with harmless organic molecules in water to produce toxic compounds
Some people feel adding chlorine to water is a risk to their health and do not want to bathe in or drink chlorinated water.
