10. Using resources (required practical 8 - water)

Question 1

What is the practical investigating?

Answer 1

analysing a sample of water for purity and describing how to purify a sample of water using distillation

Question 2

Is potable water the same as pure water?

Answer 2

no

Question 3

What does pure water not contain?

Answer 3

dissolved solids, such as salts

Question 4

What are the steps for investigating if a given sample of water is pure?

Answer 4

1. Check the pH of the water by placing a small amount of the water onto a piece of universal indicator paper
2. Universal indicator is green if the pH is 7
3. If the pH is not 7, then the water sample contains dissolved acids or alkali and is therefore not pure
4. If the pH is 7, the water still may not be pure as it could still contain dissolved solids
5. to check for those, first use a balance to weigh an empty evaporating basin and record the mass
6. fill the evaporating basin with our water sample and place this on a tripod and gauze
7. Use a bunsen burner to gently heat the water until it has all evaporated
8. Allow the evaporating basin to cool and then weigh it again
9. If the water sample contained any dissolved solids, then the mass of the empty evaporating basin will have increased
10. If the mass of the evaporating basin increased, then the water sample contains dissolved solids and is not pure. If the mass did not increase, then the sample could be pure

Question 5

Why might the sample of water still not be pure after it having a pH of 7 and not having an dissolved solids?

Answer 5

it could still contain dissolved gases

Question 6

What are the steps for purifying water using distillation?

Answer 6

1. First set up the correct apparatus
2. Then gently heat the water using a bunsen burner, so that it boils gently
3. The water will then evaporate and form steam
4. The water vapour now travels along the collecting tube
5. When the water vapour enters the cold test tube it condenses back into liquid water (this is now distilled water)

Question 7

What is distilled water?

Answer 7

Pure water