Paper 1 - Gases in the atmosphere

Question 1

What are the approximate percentages by volume of the four most abundant gases in dry air?

Answer 1

• 78% nitrogen
• 21% oxygen
• Nearly 1% argon
• 0.04% carbon dioxide

Question 2

Describe an experiment to determine the percentage by volume of oxygen in air using experiments involving the reactions of metals

Answer 2

• Soak some iron wool in acetic acid as the acid will catalyse the solution
• Push the wool into a measuring cylinder and invert the measuring cylinder into a beaker of water
• Record the starting position of the water using the scale on the measuring cylinder - this is the starting volume of air
• Over time the level of water in the measuring cylinder will rise
• This is because the iron reacts with the oxygen in the air to make iron oxide
• The water rises to fill the space the oxygen took up
• Leave the measuring cylinder until the water level stops changing
• Record the finishing position of the water - this is the final volume of air
• Calculate the percentage of oxygen in the air using start volume - final volume / start volume x 100

Question 3

Describe the combustion of magnesium in oxygen

Answer 3

• Burns with a bright white flame in air
• White powder formed in magnesium oxide
• Magnesium oxide is slightly alkaline when dissolved in water

Question 4

Describe the combustion of hydrogen in oxygen

Answer 4

• Hydrogen burns very easily in oxygen, in fact it can be explosive
• It has an orange/yellow flame and the only product is water as a vapour
• The combustion of hydrogen is often used as a test for hydrogen gas
• In small amounts, the resulting explosion gives the characteristic ‘squeaky pop’

Question 5

Describe the combustion of sulfur in oxygen

Answer 5

• Sulfur burns in air or oxygen with a pale blue flame and produces sulphur dioxide
• Sulfur dioxide is acidic when dissolved in water

Question 6

Describe the formation of carbon dioxide from the thermal decomposition of Copper (II) Carbonate

Answer 6

• Copper (II) Carbonate is a green powder that will easily decompose to form carbon dioxide and Copper (II) Oxide
• Heat Copper (II) Carbonate and collect the gas given off in a test tube
• Bubble collected gas through limewater test to test if CO2 has been collected

Question 7

What is CO2 an example of?

Answer 7

A greenhouse gas

Question 8

What could increasing amounts of CO2 in the atmosphere do?

Answer 8

It could contribute to climate change

Question 9

Describe an experiment to determine the percentage by volume of oxygen in air using experiments involving the reactions of non-metals

Answer 9

• Place the phosphorus ina tube and attach a glass syringe at either end
• Make sure one of the syringes is filled with air and the other is empty
• Heat the phosphorus and use syringes to pass the air over it - the phosphorus will react with oxygen in the air to make phosphorus oxide
• As it reacts, the amount of air in the syringes will decrease
• Measure the starting and final volumes of air using the scale on one of the syringes
• Calculate the percentage of oxygen in the air using start volume - final volume / start volume x 100