Topic 4: Gases in the Atmosphere

Question 1

What is the composition of gases in earths atmosphere in percentages?

Answer 1

• 78% - Nitrogen
• 21% - Oxygen
• 0.9% - Argon
• 0.04% - Carbon Dioxide
• 0.06% - Negligible other gases

Question 2

How can you find the percentage of oxygen in the air?

(Using Iron wool)

Answer 2

• first soak the iron wool in some acetic acid(this will catalyse the reaction)
• push the wool into the end of a measuring cylinder and invert the cylinder into a beaker of water
• record the starting level of the water on the cylinder
• over time the level of the water will rise up the cylinder
• this is because the oxygen will react with the iron and the water will replace the oxygen’s space in the cylinder
• leave for about a week or until the water level stops rising
• record the** final water level**
• to calculate the percentage use the percentage change in mass equation (start vol-finish vol/start vol x 100)

Question 3

What happens when magnesium is combusted in oxygen?

Answer 3

• An intense white flame is observed and a white powder (magnesium oxide) is produced
• Magnesium is oxidised to produce magnesium oxide

All combustions are exothermic, and can be considered oxidation reactions

Question 4

What happens when hydrogen is combusted in oxygen?

Answer 4

Hydrogen is oxidised to produce water in the form of water vapour (which is a liquid at room temperature)

Question 5

What happens when sulfur is combusted in oxygen?

Answer 5

• A blue flame is observed, and a colourless, poisonous gas is produced (sulfur dioxide)
• Sulfur is oxidised to produce sulfur dioxide

Question 6

What is the general equation for the thermal decomposition for metal carbonates?

Thermal decomposition describes the breakdown of a substance due to heat action

Answer 6

Metal carbonate –> Metal oxide + Carbon dioxide

Question 7

What is the symbol equation with state symbols for the thermal decomposition of copper carbonate?]
and what is the colour change?

Answer 7

CuCO₃(s) –> CuO(s) + CO₂(g)

Copper carbonate is a green powder which slowly darkens as copper oxide is produced
green to black colour change

Question 8

What is the greenhouse effect?

Answer 8

• Shortwave radiation from the sun passes through the atmosphere and hits the earths surface
• Some is absorbed, and some is re-emitted as infrared radiation
• However some of this re-emmited radiation is trapped by greenhouse gases in the atmosphere such as carbon dioxide, methane and water vapour which absorb and store this energy, trapping the heat

Question 9

What is the enhanced greenhouse effect?

Answer 9

• Increased levels of greenhouse gases caused by human activity (mostly carbon dioxide) in the atmopshere mean more infrared radiation (so heat energy) is being trapped inside of the earths atmosphere
• As a result, the earth is becoming hotter as levels of these greenhouse gases increase and more heat is trapped

The normal greenhouse effect is responsible for keeping the earth at a habitable temperautre, however the enhanced greenhouse effect is responsible for global warming