2.9 - 2.14 gases in the atmosphere

Percentages by volume of the 4 most abundant gases in dry air

78% nitrogen, 21% oxygen, 0.9% argon, 0.037% carbon dioxide

How to determine the percentage by volume of oxygen in air using experiments involving reactions of metals and non metals with air (example using copper)

• 100cm³ of air passed from side to side over copper that was being heated with a Bunsen burner (in a closed system so no air can get in/out)

• All oxygen in air will react with copper

• As it is passed, the volume of air will decrease

• Continue until volume stops decreasing then record the volume of remaining air and subtract from 100cm³ (original value) to find how much air was oxygen

• The reaction happening is copper + oxygen → copper (II) oxide

  • Notice black copper oxide forming

Describe the combustion of elements in oxygen

Combustion is an example of oxidation, where a substance gains oxygen

Chemical equation for combustion of magnesium in oxygen

2Mg (magnesium) + O2 (oxygen) → 2MgO (magnesium oxide)

Chemical equation for combustion of Sulfur in oxygen

S (Sulfur) + O2 (oxygen) → SO2 (Sulfur dioxide)

Chemical equation for combustion of hydrogen in oxygen

2H2 (hydrogen) + O2 (oxygen) → 2H2O (water)

Chemical equation for the thermal decomposition of metal carbonates

Metal carbonate -(heat) → metal oxide + carbon dioxide

XCO3 - heat → XO + CO2

What does the greenhouse gas effect do

Maintains temperatures on earth high enough to support Life

How does the greenhouse effect work

• electromagnetic radiation at most wavelengths from the sun passes through earth’s atmosphere

• The earth absorbs some radiation and thus warms up but some heat is radiated from the earth as infrared radiation

• Some of this radiation is absorbed by greenhouse gases In the atmosphere

• Atmosphere warms leading to greenhouse effect and global warming

Examples of greenhouse gases

Water vapour, CO2 (carbon dioxide) , CH4 (methane)