2 - Inorganic Chemistry (c) Gases in the atmosphere
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What are the approximate percentages (by volume) of the four most abundant gases in dry air?
Nitrogen - 78% Oxygen - 21% Argon - 0.9% Carbon Dioxide - 0.04%
What is combustion?
Combustion is a reaction where something is burned in the presence of oxygen to form oxides. It is exothermic and an oxidation reaction (where a substance gains oxygen) - but loses electrons
What groups can be combusted?
Both metals and non-metals
What group is carbon dioxide part of? What does this group do?
Greenhouse gases - Increasing amounts of these in the atmosphere contribute to climate change
How would you find the percentage of oxygen in air (using phosphorous)?
Measure the distance the water level rises (as oxygen is used up in combustion with phosphorous, but phosphorous is toxic, so care must be used to handle it)
What are observations of the combustion of Magnesium, Hydrogen and Sulfur?
Magnesium - Intense white flame, white (magnesium oxide) powder produced Hydrogen - Exothermic, water produced Sulfur - Blue flame, colourless, poisonous gas produced
What is thermal decomposition?
Where a substance breaks down due to the action of heat
What do carbonated (of metals int he lower half of the reactivity series) produce when thermally decomposed (heated)?
A metal oxide and carbon dioxide
Describe the thermal decomposition of Copper(II) carbonate
It produces a black copper oxide (from green copper carbonate powder) and carbon dioxide (which can be tested with limewater)
How can you determine the % of oxygen in the atmosphere using iron filings?
• Firstly, you will need to measure the volume between the final mark on the scale and the tap (stopcock) • Fill the burette with water up to lowest mark, 50.0 mL, and then let it drain into a small measuring cylinder • Measure the volume of water • Add a little water to moisten the inside of the burette • Make sure the tap is closed and sprinkle some iron filings or push a piece of iron wool into the bottom of the burette • Invert the burette into a trough of water and clamp the burette vertically • Note and record the position of the water level After 3-4 days note the new position of the water level
