Gases in the Atmosphere

Question 1

How would you calculate the percentage of oxygen in air?

Answer 1

pass 100cm3 of air over excess copper turnings whilst they are heated and the volume of air remaining should be 79cm3.
100-79=21cm3 so 21% of air is oxygen
(must wait until the apparatus has cooled because gas expands when its hot (potential for incorrect reading))

Question 2

Give the chemical equation and colours for the reaction of copper with oxygen

Answer 2

2Cu + O2 = 2CuO

Orangey-brown) (black

Question 3

Give the main components of air and their percentages

Answer 3

Oxygen-21%
Nitrogen-78%
Argon-0.93%
Carbon Dioxide-0.04%
Water Vapour-0.03%

Question 4

What are the main purposes of oxygen?

Answer 4

Essential for respiration and combustion reactions

Question 5

Describe the observations of a reaction of magnesium with oxygen

Answer 5

dazzling white flame, grey-white smoke/ash given off (MgO).

If water is added, UI turns blue-Alkaline (pH10)

Question 6

Describe the observations of a reaction of sulphur with oxygen

Answer 6

Melts, lilac/blue flame, SO2 forms.

If water is added, UI turns red-Acid (pH1)

Question 7

What solutions do metal oxides give?

Answer 7

Alkaline

Question 8

What solutions do non-metal oxides give?

Answer 8

Acidic

Question 9

Define Thermal Decomposition

Answer 9

When heat is used to split a compound into 2 or more different substances.

Question 10

Give both equations for the thermal decomposition of copper carbonate (with colours)

Answer 10

Copper carbonate = copper oxide + carbon dioxide
CuCO3(g) = CuO(s) + CO2 (g)
(Green) (Black) (Turns lime water
cloudy)

Question 11

Give 2 properties of CO2 and uses for these properties

Answer 11

1) More dense than air-used in electrical fire extinguishers to coat fire in CO2 so the fire can’t get O2
2) Water soluble-when dissolved in water under pressure, it makes H2O fizzy (carbonic acid) (fizzy drinks)

Question 12

CO2 is a greenhouse gas, how does it contribute to global warming?

Answer 12

It stops the Earth radiating heat energy back to space

It takes energy into its bonds and releases it back to Earth, warming it.

Question 13

Give the tests for CO2 and H2O, and the proof for H2O

Answer 13

CO2-bubble through lime water and it goes cloudy
H2O-anhydrous copper sulphate (white) changes to hydrated copper sulphate (blue)
H2O proof-measure the boiling/melting points 100/0