Gases in the air

Question 1

what are the four main gases in the atmosphere

Answer 1

1) Oxygen - 21%
2) Argon - < 1%
3) Carbon dioxide - 0.04%
4) Nitrogen - 78%

Question 2

how do you calculate the percentage of oxygen in the air with METAL (iron)

Answer 2

1) place wet iron fillings inside a burette
2) place the end of the burette in a trough of water. open the tap to allow water to enter the bottom
3) close the tap and record the volume of gas in the burette
4) leave the apparatus until volume of gas inside remains constant

Question 3

what do you do with the recordings to mathematically work out the percentage of oxygen in the air

Answer 3

final volume - initial volume = volume of oxygen

divide the volume by the initial volume then times by 100 to get the percent

Question 4

how do you calculate the percentage of oxygen in the air with NON-METAL (phosphorus)

Answer 4

1) float a piece of white phosphorus on a watch glass in a trough of water
2) place a bell jar over the watch glass and mark the water level outside
3) using a glass rod, tip the glass watch so that the phosphorus is touching the water
4) quickly place a bung in the top of the bell jar

Question 5

what do you do with the recordings to mathemtically work out the percentage of oxygen in the air

Answer 5

when the reaction is finished, mark the new water level

Determine the volume of gas before and after by filling the bell jar with water and measuring the volume for each mark made.

Subtract the final volume from the initial volume to determine the volume of oxygen.

Divide this value by the initial volume and multiply by 100 to calculate the percentage of oxygen in the air.