Gases in the Atmosphere

Question 1

4 most abundant gases in the air

Answer 1

Nitrogen N2 (78.1%)
Oxygen O2 (21.0%)
Argon Ar (0.9%)
Carbon dioxide CO2 (0.04)

Question 2

Determining oxygen percentage via copper

Answer 2

A syringe with 100cm^3 of air is pushed towards hot copper and into another syringe
The copper is in excess and uses up the oxygen to form CuO
All the oxygen is used up, and so the volume of the air decreases by about 20%

Question 3

Determining oxygen percentage via iron

Answer 3

Wet iron filings placed in a conical flask connected to a syringe
As long as iron and water are in excess, the total volume of air enclosed by the apparatus decreases by about 20% over several days

Question 4

Determining oxygen percentage via phosphorus

Answer 4

Phosphorus is placed on an evaporating dish in a water bath with a bell jar placed over it
The phosphorous is burnt and reacts with the oxygen in the air (P4O10) and causes the water in the bell jar to rise about 20%

Question 5

Combustion of magnesium in oxygen

Answer 5

Bright white flame produced
Leaving behind white ash of magnesium oxide

Question 6

Combustion of hydrogen in oxygen

Answer 6

Explosive reaction (in large quantities)
Basis of ‘squeak pop’ test for hydrogen in test tube (small quantities)
Leaving behind water

Question 7

Combustion of sulfur in oxygen

Answer 7

Blue flame produced
Leaving behind sulfur dioxide

Question 8

Formation of Carbon dioxide via thermal decomposition

Answer 8

On heating metal carbonates decompose into metal oxides and carbon dioxide
e.g. CuCO3 -> CuO + CO2

Question 9

How does carbon dioxide contribute to climate change

Answer 9

CO2 is a greenhouse gas
It absorbs infra-red radiation and warms the atmosphere, leading to global warming