Atmospheric Gases

Question 1

What are the main gases in the atmosphere and their proportions?

Answer 1

Nitrogen: 78%

Oxygen: 21%

Argon: nearly 1%

Carbon dioxide: only 0.04%

Variable: Water vapour

Question 2

What experiment can you use to measure oxygen in the air using iron?

Answer 2

• Soak iron wool in acetic acid
• Invert it in water inside a measuring cylinder
• Record starting position of water using scale of the measuring cylinder -> starting volume of air
• Leave for a week (iron reacts with oxygen → rust)
• Record final volume
• Use:
  (Startvol-Finalvol)
  ÷ Startvol × 100
• Answer ≈ 20% oxygen

Question 3

How can you use phosphorus to measure oxygen in air?

Answer 3

• Place phosphorus in a tube
• Attach a glass syringe at either end (make sure 1 is filled with air & other is empty)
• Heat it, pass air between syringes
• Phosphorus reacts with oxygen → phosphorus oxide
• Measure start and end air volume
• Use same formula to calculate oxygen %
  start volume - final volume / start volume x 100

Question 4

What happens when elements burn in air?

Answer 4

They react with oxygen to form oxides.

Question 5

What happens when magnesium burns in air?

Answer 5

• Bright white flame
• white powder formed is magnesium oxide (MgO)
• MgO is slightly alkaline in water

Question 6

What happens when hydrogen burns in air?

Answer 6

• Burns very easily in O2 -> can be explosive
• Pale blue flame
• Forms only water (H₂O)
• Used as a test for hydrogen: ‘squeaky pop’

Question 7

What happens when sulfur burns in air?

Answer 7

• Pale blue flame
• Produces sulfur dioxide (SO₂)
• SO₂ is acidic in water

Question 8

What is thermal decomposition?

Answer 8

When a substance breaks down with heat into simpler substances.

Question 9

What happens when copper(II) carbonate is heated?

Answer 9

• Green powder turns black
• Produces copper(II) oxide and carbon dioxide
• Equation:
  CuCO₃ → CuO + CO₂

Question 10

How can you test for the CO₂ gas from decomposition?

Answer 10

Collect gas and pass it through limewater – it turns cloudy.

Question 11

Why is CO₂ called a greenhouse gas?

Answer 11

It traps heat radiated from Earth, keeping the planet warm.

Question 12

What are examples of greenhouse gases?

Answer 12

Carbon dioxide

Methane

Water vapour

Question 13

What human activities increase CO₂ in the atmosphere?

Answer 13

• Deforestation (less CO₂ absorbed)
• Burning fossil fuels (releases locked-up carbon)

Question 14

What has happened to CO₂ levels over the last 200 years?

Answer 14

They have increased, leading to global warming.

Question 16

How does increasing CO₂ cause climate change?

Answer 16

Rising CO₂ traps heat, warming the Earth and causing changing weather, melting ice caps, and rising sea levels.