IGCSE Science C2 - Gases in the Atmosphere

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Questions and Answers

Which of the following gases are the four most abundant gases in dry air?

Nitrogen, Oxygen, Krypton, and Carbon Dioxide

Nitrogen, Oxygen, Helium, and Carbon Dioxide

Nitrogen, Oxygen, Neon, and Carbon Dioxide

Nitrogen, Oxygen, Argon, and Carbon Dioxide (correct)

What is the approximate percentage of oxygen in dry air by volume?

21%

Carbon dioxide is a greenhouse gas that can contribute to climate change.

True

What is the chemical formula for copper(II) oxide?

CuO Signup and view all the answers

What is the word equation for the reaction of copper with oxygen?

Copper + Oxygen --> Copper(II) Oxide Signup and view all the answers

What is the chemical formula for sulfur dioxide?

SO2 Signup and view all the answers

What is the chemical formula for magnesium oxide?

MgO Signup and view all the answers

What is the word equation for the reaction of magnesium with oxygen?

Magnesium + Oxygen --> Magnesium oxide Signup and view all the answers

What is the chemical formula for water?

H2O Signup and view all the answers

What is the word equation for the reaction of hydrogen with oxygen?

Hydrogen + Oxygen --> Water Signup and view all the answers

What type of compound are metal oxides classified as?

Ionic compounds Signup and view all the answers

What is the general characteristic of metal oxides in terms of their reaction with acids?

They react as bases Signup and view all the answers

What is the general characteristic of non-metal oxides in terms of their reaction with alkalis?

They react as acids Signup and view all the answers

Thermal decomposition always involves the breaking down of a substance by heating.

True Signup and view all the answers

What are the two products formed from the thermal decomposition of copper carbonate?

Copper(II) oxide and Carbon dioxide Signup and view all the answers

What is the chemical formula for calcium carbonate?

CaCO3 Signup and view all the answers

What are the two products formed from the thermal decomposition of calcium carbonate?

Calcium oxide and Carbon dioxide Signup and view all the answers

Carbon dioxide is a greenhouse gas which contributes to the greenhouse effect.

True Signup and view all the answers

The greenhouse effect is a completely artificial phenomenon caused by human activity.

False Signup and view all the answers

What are some of the potential consequences of climate change?

Melting polar ice caps, rising sea levels, and changes in weather patterns Signup and view all the answers

Study Notes

IGCSE Science - C2 Inorganic Chemistry - 2C Gases in the Atmosphere (Double)

Learning Outcomes:
- Know the approximate percentages by volume of the four most abundant gases in dry air.
- Understand how to determine the percentage by volume of oxygen in air using experiments involving reactions of metals (e.g., iron) and non-metals (e.g., phosphorus) with air.
- Describe the combustion of elements in oxygen, including magnesium, hydrogen, and sulfur.
- Describe the formation of carbon dioxide from the thermal decomposition of metal carbonates, including copper(II) carbonate.
- Know that carbon dioxide is a greenhouse gas and that increasing amounts in the atmosphere may contribute to climate change.
- Practical: determine the approximate percentage by volume of oxygen in air using a metal or a non-metal.

Composition of Air

The percentages (by volume) of the four most abundant gases in unpolluted, dry air are approximately:
- Nitrogen (N₂): 78.1% (About 4/5)
- Oxygen (O₂): 21.0% (About 1/5)
- Argon (Ar): 0.9%
- Carbon Dioxide (CO₂): 0.04%
The remainder of the air is made up of other noble gases in small amounts (helium, neon, krypton, xenon, and radon).

Measuring the Percentage of Oxygen - Practical Methods

There are three key experimental methods to determine the percentage of oxygen in air:
- Using copper
- Using the rusting of iron
- Using phosphorus
All methods depend on the reaction of a substance with oxygen in the air and measuring the decrease in volume.

Using Copper - Practical Details

Apparatus:
- Silica tube packed with copper filings
- Gas syringe (initially set to 100 cm³)
- Bunsen burner (for heating).
Equation: 2Cu (s) + O₂ (g) → 2CuO (s)
Procedure:
- Heat the silica tube containing copper strongly using a Bunsen burner.
- Pass air over copper, taking readings from the gas syringe over a week's time. The volume in the syringe decreases as oxygen is used up and the resulting copper(II) oxide will have turned black.
Calculations:
- Volume of oxygen = Initial volume - Final volume
- Percent of oxygen = (Volume of oxygen / Initial volume) x 100

Using Copper - Key Points

Ensure all oxygen reacts (copper must be in excess).
Cool the apparatus before taking the final reading, as gases expand when hot.
Values are typically between 18% and 24%, not precisely 21%.

Using Rusting of Iron - Practical Details

Apparatus:
- Conical flask
- Connecting tube
- Measuring cylinder
- Wet iron filings
- Gas syringe (to measure volume).
Equation: 4Fe (s) + 3O₂ (g) + 6H₂O (l) → 4Fe(OH)₃ (s)
Procedure:
- Set up the apparatus shown, including adding iron filings to the flask.
- Measure the initial and final volume in the gas syringe to calculate the volume of oxygen used up during the process.
Calculations:
- Total Initial Volume = sum of initial volumes of air in different components.
- Volume of oxygen = Initial total volume - Final total volume
- Percent of Oxygen = (Volume of oxygen / Total initial volume) x 100

Using Rusting of Iron - Key Points

The total volume used in calculations includes the conical flask and connecting tube.
Ensure the iron is in excess.
The experiment usually takes at least a week.

Using Phosphorus - Practical Details

Apparatus:
- Evaporating basin
- Bell jar
- Trough (water)
- Phosphorus sample
- Measuring cylinder
Equation: 4P(s) + 5O₂(g) → 2P₂O₅(s)
Procedure:
- Set up the apparatus and place phosphorus in the bell jar.
- Measure and record initial and final water level to determine the volume of oxygen that has reacted.

Using Phosphorus - Key Points

Phosphorus must be in excess to ensure all oxygen reacts.
For safety, this experiment should be carried out by a teacher. Similar experiments can be performed by students using a candle, petri dish, and measuring cylinder.
Values are typically between 18% and 24%, not 21%.

Combustion of Elements in Oxygen

Some elements burn more brightly and react rapidly in pure oxygen than in air.
Key elements include magnesium, sulfur, and hydrogen which form MgO, SO₂ and H₂O respectively

Thermal Decomposition

Carbon dioxide can be formed from thermal decomposition of metal carbonates, such as copper carbonate or calcium carbonate.
Metal carbonates decompose into metal oxide and carbon dioxide.
Thermal decomposition is the process of breaking something down by heating.

Greenhouse Effect

Carbon dioxide formed from burning fossil fuels contributes to the greenhouse effect, trapping heat in the atmosphere.
The greenhouse effect is a natural process, but increasing CO₂ levels cause climate change.
Impacts include melting polar ice, rising sea levels, and extreme weather.

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Description

Test your knowledge on the composition of air and the properties of gases found in the atmosphere with this quiz! Covering elements such as nitrogen, oxygen, and carbon dioxide, you'll explore their roles, reactions, and implications for climate change. Perfect for IGCSE students studying Inorganic Chemistry.