EXERCISE - AQUEOUS SOLUTIONS AND WATER QUALITY
As you read through pages 357-362, answer the following questions:
1) What % of the world’s fresh water does Canada have?
2) Look at the data in Table 9.5. Did you realize that it is acceptable to have small amounts
of substances such uranium, mercury and insecticides in drinking water?
3) a) What type of bacteria in the water supply caused 7 people to die and many to become
ill in Walkerton, Ont. in 2000?
b) What should the town’s water manager have done to deal with this problem?
Sources That Compromise Water Quality
1) State three examples of point sources of pollution.
2) State one example of a diffuse source of pollution.
3) State one example of an indirect source of pollution.
Treating Water for Your Home
1) Briefly describe the six processes that take place at a water treatment plant.
2) Why do some municipalities add sodium fluoride to drinking water?
Hard Water and Soft Water/Treating Water at Home
1) Distinguish between hard water and soft water.
2) What is the most common type of rock that causes hard water?
3) Where is boiler scale commonly found and what problems does it cause?
4) a) In an ion exchange water softener, what ion exchanges with the calcium and other
hardness causing ions in the water?
b) Why is this kind of water softener not the best choice for some people?
Waste-Water Treatment
What does each of the following mainly involve:
1) primary waste-water treatment?
2) secondary waste-water treatment?
3) tertiary waste-water treatment?
Solution Stoichiometry
Read The Concentration of Ions Sample Problem on pages 348-349.
Then, do question 8 on page 352.
(You can check your answer to this question on page 367.)
Answers – Aqueous Solutions and Water Quality
1) Canada has 22% of the world’s fresh water.
2) Most students say no.
3) a) It was E. coli bacteria in the water supply that caused the problem.
b) The town’s water manager should have increased the concentration of chlorine in
the town’s water supply.
Sources That Compromise Water Quality
1) -
wrecked tankers that leak oil.
factories that discharge metallic ions, organic compounds, acids and bases.
thermal power plants discharge warm water into a lake from their cooling towers.
2) A heavy downpour can cause run-off from farm fields to enter rivers and lakes. This run-off
often carries undesirable pollutants.
3) Motor vehicles and factory smokestacks release gases that can indirectly cause many
different types of pollution.
Treating Water for Your Home
1) -
a coarse screen made of metal bars filters large particles and trash.
chlorine is added to kill bacteria and viruses.
lime and aluminum sulphate are added to form aluminum hydroxide that traps finely
suspended particles and settles to the bottom of the tank.
the water is passed through a bed of graded gravel and sand in a filtering tank.
water is often saturated with oxygen by spraying it into the air, which helps to remove
volatile organic compounds and improves the taste and odour.
the water receives a second treatment with chlorine to kill bacteria.
2) Sodium fluoride helps to strengthen tooth enamel and thus prevent tooth decay.
Hard Water and Soft Water/Treating Water at Home
1) Water with high concentrations of Ca2+, Mg2+ and other ions is called hard water, partly
because it is hard to lather. Water with relatively low concentrations of these ions lathers
well and is called soft water.
2) The most common type of rock to cause hard water is limestone (calcium carbonate).
3) These deposits form a coating on heating elements in kettles and boilers, and build up
inside hot water pipes. It reduces the flow of water in pipes and increases the cost of
heating water.
4) a) Sodium ions exchange with the calcium and other hardness causing ions in the water.
b) This type of water treatment adds significant amounts of sodium to the water. Thus, it
may not be the best choice for drinking water. This is especially true for people on
sodium-restricted diets.
Waste-Water Treatment
1) Primary treatment mainly involves removing solids from waste water physically, using
filters and settling tanks.
2) Secondary treatment involves using bacteria to chemically decompose dissolved and
suspended organic compounds.
3) Tertiary treatment involves chemical treatments to remove the majority of remaining ions
and disease-causing micro-organisms.