Topic 3 - GASES IN THE ATMOSPHERE

Question 1

What is the composition of the air? (%)

Answer 1

NITROGEN = 78%
OXYGEN = 21%
CARBON DIOXIDE = 0.9%
ARGON = 0.04%

Question 2

Describe the method of experimenting the % by volume of oxygen in air using a METAL

Answer 2

IRON:
-place wet iron fillings at end of burette (use vaseline if iron fillings font stick)
-use a clamp to hold burette vertically in trough of water
Meeasure + note starting height of water level in burette
-leave apparatus for weeks
-measure + note final height of water level in burette.

Question 3

What would be the RESULTS of the experiment using IRON to calculate the % by volume of oxygen in air?

Answer 3

• after several days, water rise up burette + reach constant level a s iron fillings will react with all oxygen in air to form iron(iii) oxide(rust).
• water level will rise to replace volume of oxygen lost during reaction.

EXAMPLE: original water level (15cm2) and now is (12cm2). - 3cm2 used up

3 / 15 x 100 = 20% OXYGEN IN AIR

Question 4

How do you calculate the % volume of oxygen?

Answer 4

volume of O2 used / volume of air at start x 100

=% of O2

Question 5

Describe the method of experimenting the % by volume of oxygen in air using a NON-METAL

Answer 5

PHOSPHORUS:

• add phosphorus to evaporating dish + place it in trough of water (making sure it is floating)
• burn phosphorus using candle + cover with bell jar
• measure + note starting height of water level in bell jar
• leave for several days
• measure + note final height of water level in bell jar

Question 6

What would be the RESULTS of the experiment using PHOSPHORUS to calculate the % by volume of oxygen in air?

Answer 6

• after several days, water rises up bell jar + reach constant level as phosphorus will use up O2 in air IN ORDER TO BURN. (air is one of 3 elements a fire needs)
• water level rises to replace volume of oxygen lost during this reaction

Question 7

What is combustion?

Answer 7

Chemical reaction involving burning

Question 8

Observation when MAGNESIUM combusts (+symbol equation)

Answer 8

intense white flame + white powder produced (magnesium oxide)
2Mg + O2 —> 2MgO2

Question 9

Observation when HYDROGEN combusts (+symbol equation)

Answer 9

exothermic + water produced

2H2 + O2 —> 2H2O

Question 10

Observation when SULPHUR COMBUSTS (+symbol equation)

Answer 10

blue flame + colourless poisonous gas produced

S + O2 —> SO2

Question 11

What is THERMAL DECOMPOSITION?

Answer 11

breaking down using heat

Question 12

What is THERMAL DECOMPOSITION OF METAL CARBONATES?

Answer 12

CO2 produced when metal carbonates are heated through thermal decomposition

Question 13

WORD EQUATION FOR METAL CARBONATES THROUGH THERMAL DECOMPOSITION

Answer 13

METAL CARBONATE —> METAL OXIDE + CO2