Water Ch. 20 Flashcards
What is Hard Water?
Water that will not form a lather easily with soap.
What is Temporary Hardness?
Hardness in water that can be removed by boiling.
What is Temporary Hardness caused by?
Hydrogencarbonate anions (Mg(HCO3)2 or Ca(HCO3)2
Chemical formula for temporary hardness
H2O + CO2 + CaCO3 -> Ca(HCO3)2
What happens when you boil temporary hardness?
Ca(HCO3)2 + Heat -> CaCO3 + CO2 + H2O
Forms Limescale
What is Permanent Hardness?
Hardness in water that can only be removed by methods other than boiling (ion exchange, distillation, deionization)
What is Permanent Hardness caused by?
Caused by the chlorides and sulfates of calcium and magnesium.
What is Ion Exchange?
Involves the water being passed through a resin where the Mg++ or Ca++ is replaced by Na+ ions
2RNa + Ca++ -> R2Ca +2Na+
What is Deionization?
Cations that cause Hardness are replaced by H+ ions and Anions are replaced by OH-, they then combine to form H2O resulting in no ions being in the water.
What is Distillation?
Removes not only the ions from the water but also the suspended solids and gases contained within the water, resulting in a pure distillate.
How do you distinguish between carbonate and hydrogencarbonate?
Add Magnesium Sulfate, the carbonate forms a precipitate while the hydrogencarbonate does not.
How do you test for Sulfate anions?
Both Sulfate and Sulfate anions react with Barium Chloride to form a white precipitate, you can then distinguish between the two by adding HCL, Barium Sulfite reacts while the Sulfate does not.
How to test for chlorine anions?
Chlorine anions react with silver nitrate to form a white precipitate of silver chloride.
How to test for nitrate anions?
Using cold freshly prepared Iron(II) sulfate and slowly adding concentrated sulfuric acid after a few moments a brown ring will form. (Known as “Brown Ring Test”)
How do you test for phosphate anions?
Using ammonium molybdate and concentrated nitric acid, you warm the solution gently to no greater than 40°C and a yellow precipitate should form if the anions are present.
What are the steps for water treatment?
Flocculation, Sedimentation, Filtration, Chlorination, Fluoridation, pH adjustment
Name a flocculating agent
Aluminium Sulfate
What is Flocculation?
Small particles clump together to facilitate settlement
What is Sedimentation?
Water is allowed to stand in tanks, allowing suspended particles to sink to the bottom.
What is Chlorination
Chlorine or sodium hypochlorite added to water to kill pathogens and micro organisms
What is Fluoridation?
Fluoride ions are added to prevent tooth decay
How is the pH of water adjusted?
Lime is added to acidic water, or sulfuric acid added to alkaline water to adjust the range of the pH to 6-8
What is the primary treatment of sewage
Involves screening and settlement, and it is a physical process which removes solids.
What is secondary treatment?
Is a biological process involving the oxidation by micro-organisms of the nutrients present in effluent.
