Chemistry 3 Unit 2

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Author:
Rvynvega
ID:
220119
Filename:
Chemistry 3 Unit 2
Updated:
2013-05-18 08:41:37
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Unit 2:Water
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  1. What is meant by soft water?
    Soft water is water that lathers easily with soap
  2. Why does hard water need more soap?
    • Hard water needs more soap to produce lather to wash effectively.
    • This is because hard water contains dissolved compounds to react with the soap to produce scum
  3. What is scum and how is it formed?
    This is an insoluble solid which is the precipitate formed when soap reacts with calcium or magnesium ions in hard water
  4. Why do soap-less detergents not form scum?
    Because there is no soap to react with the Calcium or magnesium ions in hard water
  5. How do you distinguish permanent hard water from temporary hard water?
    Temporary hard water softens when boiled, permanent hard water stays hard
  6. What does temporary hard water contain?
    Hydrogen-carbonate ions
  7. How is temporary hard water softened by heating?
    • Temporary hard water contains hydrogen-carbonate ions that decompose when heated to produce carbonate ions, water and carbon dioxide
    • 2HCO3 ~> CO3 + H2O + CO2
  8. What does the carbonate ions react with during the softening of temporary hard water?
    Carbonate ions react with calcium and magnesium ions to produce precipitates of calcium carbonate and magnesium carbonate, that are deposited as scale
  9. What is the disadvantage of using hard water?
    Hard water can increase costs because more soap is needed to wash effectively
  10. What is a disadvantage of temporary hard water?
    When temporary hard water is heated it can produce scale which can reduce the efficiency of the heating system and cause blockages
  11. What is an advantage of using hard water?
    • Hard water contains calcium compounds which are good for our health
    • Helps the development of strong bones and teeth
    • Can help reduce the risk of heart disease
  12. How can hard water be softened?
    Hard water can be softened by removing the calcium and magnesium ions which react with soap
  13. State the methods in which hard water is made soft?
    • Add sodium carbonate. This reacts with the calcium and magnesium ions to form solid precipitates of calcium carbonate and magnesium carbonate which cannot react with soap
    • Use ion-exchange columns containing sodium and hydrogen ions(resin). This resin carries the calcium and magnesium ions and sodium and hydrogen ions replace them as they pass through the column
  14. What should drinking water not contain?
    High levels of dissolved salts and microbes
  15. What is the process in which quality water is produced?
    • Choosing an appropriate water source
    • Sedimentation or filtration of the water removes any solids
    • The water is then sterilised with chlorine to kill microbes
  16. What do water filters contain and what do they do?
    Water filters contain carbon, silver and ion-exchange resins that remove dissolved substance from the water to improve the taste
  17. How is pure water obtained?
    Distillation
  18. What is the problem with distillation of water?
    Distillation requires a large amount if energy to boil the water; therefore it would be very expensive to do on a large scale

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