Water

Question 1

Give 6 properties of water

Answer 1

1. Freezing point is 0©, boiling point is 100©
2. Water expands as it freezes
3. The density of water is 1 g/cm³ but the density of ice is 0.92 g/cm³
4. Water is an excellent solvent
5. Water turns white anhydrous copper sulfate blue
6. Water clings to glass which explains the shape of the meniscus of water

Question 2

What are the 5 stages of treating water?

Answer 2

1. Screening - Passing water through a wire mesh to remove large debris
2. Settling - Water flows into large tanks called sedimentation tanks where alum is added to the water which takes out the cloudiness from the suspended particles in the water to leave it clear
3. Filtration - The water is passed through filtration beds to remove even the smallest particles of dirt
4. Chlorination - Chlorine is added to water in small amounts to kill bacteria and sterilise the water
5. Fluoridation - Sodium fluoride is added in small amounts to prevent tooth decay

Question 3

How do you show the presence of dissolved solids in a sample of water?

Answer 3

1. Put a clock glass with tap water in it over a Pyrex beaker of boiling water
2. Observe results once all the water has evaporated
3. The solid material remaining in the clock glass is in water to add a refreshing taste

Question 4

What is hard water?

Answer 4

Water that does not easily form a lather with soap

Question 5

What is the word equation for calcium hydrogencarbonate?

Answer 5

Calcium carbonate + carbon dioxide + water —–> calcium hydrogencarbonate

Question 6

How do you test samples of water for hardness?

Answer 6

1. Add a fixed volume of water from each sample (hard, sea, tap, rain, distilled) into 5 test tubes
2. Add 2 cm³ of soap solution to each sample
3. Shake each sample and wait 20 seconds, if the lather remains then that is the volume of soap required to form a lather
4. Continue adding 2 cm³ of soap solution until a lather is formed
5. The sample that uses the most soap solution to form a lather is the hardest (sea water) while the sample that uses the least soap solution is the softest (distilled water)

Question 7

Give 2 methods of removing hardness in water

Answer 7

Boiling

Ion exchange in an ion exchange resin

Question 8

Give 3 advantages and 3 disadvantages of hard water

Answer 8

Advantages:
Provides calcium for teeth and bones
Nicer taste
Good for brewing/tanning

Disadvantages:
Blocks pipes, leaves scale on kettles and boilers
Wastes soap
Produces scum

Question 9

What is the apparatus used in electrolysis

Answer 9

Hoffman VOLTAmeter

Question 10

What is electrolysis?

Answer 10

The production of a chemical change by electricity