3- Water Flashcards
Why does hard water take more soap to lather?
Hard water contains dissolved compounds that react with soap to form an insoluble solid called scum (unless you use soap less detergents)
How does water naturally become hard?
When in contact with rocks, if calcium and magnesium ions dissolve into the water
What is scale and why can it be a problem?
When temporary hard water is heated, it produces an insoluble solid called scale. This can build up in appliances such as kettles and make them less efficient
What is a benefit of drinking hard water?
Calcium compounds are good for health, they help develop strong bones and teeth and can reduce heart disease
What is the key difference between hard and soft water?
Soft water lathers easily with soap, hard water uses more soap to produce lather (wash effectively). Because hard water contains dissolved salts
How can hard water be made soft?
Removing dissolved calcium and magnesium ions that react with soap
What is the difference between temporary and permanent hard water?
Temporary hard water is softened by boiling because the calcium and magnesium ions are removed forming scale. Boiling has no effect on hard waters hardness
How is temporary hard water softened by heating?
Hydrogencarbonate ions decompose to produce carbonate ions, water and carbon dioxide. 2HCO3 –> CO3 + H2O + CO2.
Carbonate ions react with calcium and magnesium ions in water to produce scale
How can you soften permanent hard water?
Precipitating the necessary ions using washing soda (sodium carbonate)
Using an ion exchange column packed with resin (sodium and hydrogen ions). Sodium and hydrogen ions take the place of the calcium and magnesium ions which are attached to the resin
How is water treated?
After sedimentation and filtration to remove solids, chlorine kills microbes (disinfecting)
How do water filters improve the taste of water?
Carbon and an ion exchange resin remove some soluble substances to prevent the growth of bacteria
Why do we not make pure water through distillation?
The energy needed to boil the water would be too expensive on a large scale
What is the disadvantages of hard water?
It causes heating and washing systems problems
What is the problem with disinfecting water with chlorine?
It is poisonous, so must be managed carefully to minimise its impact
What is added to water supplies to prevent tooth decay?
Fluoride
