2. Gasses in the Atmosphere
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Percentage composition of air
• Nitrogen 78% • Oxygen 21% • Argon 0.9% • Carbon Dioxide 0.04%
Are combustion reactions exothermic or endothermic?
Exothermic
Magnesium observations with oxygen
• Intense white flame • White powder produced (magnesium oxide)
Hydrogen observations with oxygen
• Exothermic • Water is produced
Sulfur observations with oxygen
• Blue flame • Colourless, poisonous gas produced
What are combustion reactions classified as?
Oxidation Reactions
What is thermal decomposition?
Thermal decomposition is the term used to describe reactions where a substance breaks down due to the action of heat.
Thermal decomposition metal carbonate general formula
metal carbonate → metal oxide + carbon dioxide
What colour is copper (II) carbonate and copper oxide?
Copper(II) carbonate is a green powder and slowly darkens as black copper(II) oxide is produced.
How to test which metal carbonate reacts fastest
The carbon dioxide given off can be tested by passing the gas through limewater and looking for which metal carbonate turns milky the fastest. Ensure to use the same mass of each metal.
State three greenhouse gasses
• Carbon dioxide • Methane • Water vapour
Sources of carbon dioxide
• Combustion of wood and fossil fuels • Respiration of plants and animals • Thermal decomposition of carbonate rocks • The effect of acids on carbonates
Explain why an increasing amount of carbon dioxide in the atmosphere is likely to cause a problem for the environment.
• Carbon dioxide is a greenhouse gas • That causes climate change / global warming • Melting of polar icecaps / flooding / wildfires/ sea levels rising
Why does the water level rise in the phosphorus experiment?
Because oxygen is used up, the pressure inside the container decreases, so higher outside air pressure pushes the water up into the container.
How can iron be used to find the percentage of oxygen in air?
Iron reacts with oxygen to form rust, which removes oxygen from the air.
What do you measure in the iron experiment?
The decrease in air volume after the iron has reacted.
How do you calculate the percentage of oxygen?
Decrease in air volume ÷ original air volume × 100
How can phosphorus be used to find the percentage of oxygen in air?
Phosphorus burns in air and uses up the oxygen.