Hardness of Water

HideShow resource information

Hardness of Water

  • soft water gives a nice lather with soap but with hard water, scum and scale are produced.
  • dissolved calcium ions and magnesium ions in water react with soap making scum which is insoluble
  • when heated, hard water forms furring or scale mostly calcium carbonate on the inside of pipes, boilers and kettles. Badly scaled-up pipes and boilers reduce the efficiency of heating systems and may need to be replaced. Scale eventually blocks pipes 
  • Scale can be a thermal insulator = the kettle with scale on the heating element takes longer to boil that clean a non-scaled-up kettle - it becomes less efficient. 
  • most hard water is hard because it contains calcium ions and magnesium ions 
  • rain falling on some typre of rock can dissolve compounds like magnesium sulfate and calcium sulfate which are both soluble rocks
  • calcium ions are good for healthy teeth and bones and studies have shown that people who live in hard water areas are at less risk of developing heart disease.
1 of 4

Hard Water to Soft Water

  • by removing the calcium ions and magnesium ions, it makes the hard water soft 
  • there are two kinds of hardness - temporary and permanent
  • temporary = caused by hydrogencarbonate ion 
  • permanent = caused by dissolved calcium sulfate 
  • temporary hardness is removed by boiling, when heated, the calcium hydrogencarbonate decomposes forming calcium carbonate which is insoluble. 
  • calcium hydrogencarbonate ---> calcium carbonate + water + carbon dioxide 
  • both types of hardness can be softened by adding sodium carbonate to it. The added carbonate ions react with the calcium and magnesium ions making insoluble precipitate of calcium carbonate and magnesium carbonate. The calcium and magnesium ions are not dissolved in the water so they can't make it hard 
  • both types of hardness can also be removed by running water through "ion exchange columns" sold in shops. The columns have loys of sodium ions or hydrogen ions and "exchange" them for calcium or magnesium ions in the water 
2 of 4

Water Quality

  • water must be free from poisonous salts and harmful microbes. Microbes can cause diseases. 
  • most drinking water comes from reservoirs, water flows into reservoirs from rivers and groundwater so water companies build their reservoirs where there is a good supply of clean water.
  • water from reservoirs goes through a process of passing through a mesh screen to remove large objects such as twigs. Then, chemicals are added to make solids and microbes stick together and fall to the bottom. After, the water is filtered through gravel beds to remove all solids. Finally, water is chlorinated to kill off any harmful microbes left. 
  • Filters can be brought containing carbon or silver to remove substances from tap water. Carbon in filters removes chlorine taste and silver kills bugs 
  • totally pure water with nothing dissolved in it can be produced through distillation - boiling water to make steam and condensing steam, this is an expensive process as a lot of energy is needed so is not used to produce tap water 
3 of 4

Water Quality

  • flouride and chlorine have disadvantages when added to water:
  • flouride is added to drinking water as it helps reduce tooth decay and chlorine is added to prevent disease. 
  • studies have linked that adding chlorine to water increases certain cancers. Chlorine can react with natural sustances in water to produce toxic by-products which may cause cancer.
  • in high doses, flourine can cause cancer and bone problems in humans, so people say flourine shouldn't be added. people say they shouldn't mass medicate - people can choose whether to use flouride toothpaste but they can't choose whether they drink flouride water.
  • levels of chemicals added to drinking water need to be carefuloly monitored. 
4 of 4

Comments

No comments have yet been made

Similar Chemistry resources:

See all Chemistry resources »See all Water hardness and solubility resources »