Topic 0- Water

Question 1

describe the combustion of hydrogen

Answer 1

hydrogen burns when heated in the air or oxygen to form water. The product will be formed initially as water vapour, but if cooled it can be condensed to form water

Question 2

how do you test for water by using anhydrous copper sulfate?

Answer 2

add the liquid you are testing to anhydrous copper sulfate. The white powder will turn blue if there is water present in the liquid

Question 3

what is the test to show whether water is pure?

Answer 3

boil the liquid and measure its boiling point. If its water, its boiling point will be 100°C

Question 4

describe the laboratory preparation of oxygen from hydrogen peroxide, using manganese oxide as a catalyst

Answer 4

oxygen is most easily made in the lab from hydrogen peroxide solution using manganese oxide as a catalyst. The reaction is known as the catalytic decomposition (splitting up using a catalyst) of hydrogen peroxide. The oxygen produced is collected in an inverted glass cylinder by the downward displacement of water in a trough. Hydrogen peroxide, decomposes slowly to form water and oxygen. The speed of the decomposition is increased by adding solid manganese dioxide, which acts as a catalyst. The oxygen can also be collected over water. Since oxygen is not very soluble in water, very little is lost

Question 5

what percentage of oxygen is there in the air?

Answer 5

21%

Question 6

what percentage of carbon dioxide is there in the air?

Answer 6

0.04%

Question 7

what percentage of nitrogen is there in the air?

Answer 7

78%

Question 8

what percentage of argon is there in the air?

Answer 8

0.9%

Question 9

how can experiments involving copper, iron and phosphorus be used to investigate the percentage of oxygen by volume in the air?

Answer 9

pass 100cm3 of air from a gas syringe on one side over some copper being heated with a bunsen, to a gas syringe opposite. All the oxygen in the air will react with the copper. No air could get in or out the system while it is passed to and fro between the syringes. The volume of air should go down. Keep passing the air until the volume stops decreasing, and record the volume of the air. There should be 79cm3 of air left as 21cm3 of the original 100cm3 was oxygen that reacted with the copper to form black copper oxide. (can use iron or phosphorus also)