What is meant by the composition of the atmosphere ?

The composition of the atmosphere is the proportion of different gases present in air. It has remained largely unchanged for around 200 million years .

True or False? Oxygen makes up approximately 80% of the atmosphere.

False. Oxygen makes up approximately 20% (one-fifth) of the atmosphere. It is nitrogen that makes up approximately 80% (four-fifths).

The atmosphere is made up of approximately .......... nitrogen and .......... oxygen, with small amounts of other gases such as carbon dioxide and water vapour.

The atmosphere is made up of approximately 80% nitrogen and 20% oxygen, with small amounts of other gases such as carbon dioxide and water vapour.

How can burning phosphorus be used to find the percentage of oxygen in air?

Burning phosphorus can determine the percentage of oxygen because it burns inside a bell jar sitting in a trough of water, using up the available oxygen. As the oxygen is consumed, the water level rises inside the jar. Careful measurements of water levels before and after allow the percentage to be calculated.

Why is phosphorus a suitable substance for finding the percentage of oxygen in air?

Phosphorus is suitable because it burns readily in air and continues to burn until all the available oxygen is used up. This ensures an accurate measurement of the oxygen removed.

True or False? Phosphorus is considered safe to handle and has no significant hazards.

False. Phosphorus is toxic , so it is hazardous and must be handled with great care.

Gases in the atmosphere and their approximate percentages: Gas Approximate % Nitrogen Oxygen Carbon dioxide, water vapour, noble gases

Gases in the atmosphere and their approximate percentages: Gas Approximate % Nitrogen ~80% Oxygen ~20% Carbon dioxide, water vapour, noble gases small/trace amounts

How does the water level inside a bell jar change when phosphorus burns in air, and why?

The water level rises inside the bell jar. This is because the burning phosphorus uses up the oxygen , reducing the volume of gas inside the jar.

What is the aim of this practical?

The aim is to determine the percentage of oxygen in air using the oxidation of iron (iron filings or iron wool).

In the burette practical, iron filings are placed inside an inverted burette in a trough of water. After 3-4 days, the water level .......... because the iron has .......... (reacted with) the oxygen.

In the burette practical, iron filings are placed inside an inverted burette in a trough of water. After 3-4 days, the water level rises because the iron has oxidised (reacted with) the oxygen.

How is the percentage of oxygen in air calculated from the burette experiment?

The percentage of oxygen is calculated by finding the initial volume of air and the final volume of air (after oxygen is removed). Volume of oxygen = initial volume − final volume. Percentage = (volume of oxygen ÷ initial volume) × 100.

True or False? The water level in the burette rises after 3-4 days because oxygen has been used up by the rusting iron.

True. Iron undergoes oxidation (rusting), reacting with the oxygen in the air inside the burette and causing the water level to rise.

Why must you wait 3-4 days before recording the final water level in the burette experiment?

You must wait 3-4 days because the iron takes time to fully oxidise (rust) and use up all the available oxygen in the burette. Reading too early would give an incomplete result.

Using the example data below, complete the calculation table: Measurement Value (mL) Volume between 50 mL mark and tap 3.8 Initial water level 2.6 Final water level 12.7 Initial volume of air Final volume of air Volume of oxygen

Measurement Value (mL) Volume between 50 mL mark and tap 3.8 Initial water level 2.6 Final water level 12.7 Initial volume of air (50.0 + 3.8) − 2.6 = 51.2 Final volume of air 53.8 − 12.7 = 41.1 Volume of oxygen 51.2 − 41.1 = 10.1

Combustion is the scientific word for burning. It is a chemical reaction in which oxygen reacts with elements or compounds to produce oxides .

Why are combustion reactions always exothermic ?

Combustion reactions always give out heat to the surroundings, making them exothermic .

True or False? Combustion reactions can be classified as oxidation reactions.

True. Combustion always involves reaction with oxygen , which means the substances are being oxidised . Combustion is therefore a type of oxidation reaction.

Complete the table of observations for the combustion of elements: Element Observation during combustion Magnesium Hydrogen Sulfur

Element Observation during combustion Magnesium Intense white flame; white powder (magnesium oxide) produced Hydrogen Exothermic; water produced Sulfur Blue flame; colourless, poisonous gas produced

What product is formed when sulfur burns in oxygen?

When sulfur burns in oxygen, sulfur dioxide (SO 2 ) is formed. It is a colourless, poisonous gas.

What are the products when magnesium burns in oxygen, and what observation is made?

Burning magnesium produces magnesium oxide (MgO), a white powder. The reaction produces an intense white flame .

True or False? Water is produced when hydrogen burns in oxygen.

True. When hydrogen burns in oxygen, the product is water (H 2 O). The equation is: 2H 2 (g) + O 2 (g) → 2H 2 O (g).

What is the symbol equation for the combustion of magnesium ?

The equation is: 2Mg (s) + O 2 (g) → 2MgO (s)

When sulfur burns in oxygen, a .......... flame is produced and the gas .......... is formed, which is colourless and poisonous.

When sulfur burns in oxygen, a blue flame is produced and the gas sulfur dioxide (SO 2 ) is formed, which is colourless and poisonous.

Define thermal decomposition .

Thermal decomposition is a reaction in which a substance breaks down due to the action of heat .

What are the products of the thermal decomposition of a metal carbonate?

The products of thermal decomposition of a metal carbonate are a metal oxide and carbon dioxide gas.

When copper(II) carbonate is heated, it decomposes to form .......... and .......... .

When copper(II) carbonate is heated, it decomposes to form copper(II) oxide and carbon dioxide .

True or False? Copper(II) carbonate is a black powder that turns green when heated.

False. Copper(II) carbonate is a green powder. When heated, it slowly darkens as black copper(II) oxide is produced.

How can you test that carbon dioxide gas has been produced in the thermal decomposition of copper(II) carbonate?

To test for carbon dioxide , pass the gas through limewater . If carbon dioxide is present, the limewater turns milky (cloudy).

What is the word equation for the thermal decomposition of copper(II) carbonate?

The word equation is: copper(II) carbonate → copper(II) oxide + carbon dioxide

True or False? The release of carbon dioxide from calcium carbonate in cement production contributes to rising atmospheric CO 2 levels.

True. The release of carbon dioxide from calcium carbonate in cement production is a contributing source of increased atmospheric CO 2 , which contributes to the enhanced greenhouse effect .

Complete the table for the thermal decomposition of copper(II) carbonate: Details Starting material Copper(II) carbonate Colour of starting material Products Colour change observed Test for gas produced

Details Starting material Copper(II) carbonate Colour of starting material Green Products Copper(II) oxide and carbon dioxide Colour change observed Green to black (as copper(II) oxide forms) Test for gas produced Limewater turns milky

What is the greenhouse effect ?

The greenhouse effect is the process by which greenhouse gases in the atmosphere trap heat energy, keeping the Earth's surface warm enough to support life.

What happens to short wavelength radiation from the Sun when it reaches Earth?

Short wavelength ultraviolet radiation from the Sun strikes the Earth's surface. Some is absorbed by the surface, and some is re-emitted as long wavelength infrared radiation.

True or False? Greenhouse gases trap long wavelength infrared radiation in the atmosphere.

True. Greenhouse gases absorb and store infrared (long wavelength) radiation re-emitted from the Earth's surface, trapping heat in the atmosphere.

The Sun emits .......... wavelength radiation. When this strikes the Earth's surface, some is re-emitted as .......... wavelength radiation, which is trapped by .......... gases.

The Sun emits short wavelength radiation. When this strikes the Earth's surface, some is re-emitted as long wavelength radiation, which is trapped by greenhouse gases.

Name the three main greenhouse gases.

The three main greenhouse gases are: Carbon dioxide Methane Water vapour

How do increasing levels of carbon dioxide and methane affect the greenhouse effect?

Increasing levels of carbon dioxide and methane trap extra heat energy in the atmosphere, even though they are present in small amounts. This contributes to global warming .

True or False? Without any greenhouse gases, the Earth's surface temperature would be stable and comfortable.

False. Without greenhouse gases , the Earth's surface would swing between extreme heat and extreme cold. Greenhouse gases maintain a mean global temperature of around 15°C .

What is the difference between the greenhouse effect and the enhanced greenhouse effect ?

The greenhouse effect is the natural process that keeps Earth's mean temperature around 15°C . The enhanced greenhouse effect is caused by increased greenhouse gas concentrations, which most scientists believe is leading to global warming .

Complete the table about the greenhouse effect: Feature Detail Type of radiation emitted by Sun Type of radiation re-emitted by Earth's surface Gases that trap this radiation Effect on Earth's temperature

Feature Detail Type of radiation emitted by Sun Short wavelength (ultraviolet) Type of radiation re-emitted by Earth's surface Long wavelength (infrared) Gases that trap this radiation Greenhouse gases (e.g. CO 2 , methane, water vapour) Effect on Earth's temperature Temperature is kept high enough to support life

IGCSEChemistryEdexcelChemistry (Modular)Unit 2Flashcards6. Inorganic Chemistry: Part 2Gases in the atmosphere

Gases in the atmosphere (Edexcel IGCSE Chemistry (Modular): Unit 2): Flashcards

Exam code: 4XCH1

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FrontComposition of Air
What is meant by the composition of the atmosphere?

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Cards in this collection (40)

What is meant by the composition of the atmosphere?
The composition of the atmosphere is the proportion of different gases present in air. It has remained largely unchanged for around 200 million years.
True or False?
Oxygen makes up approximately 80% of the atmosphere.
False.
Oxygen makes up approximately 20% (one-fifth) of the atmosphere. It is nitrogen that makes up approximately 80% (four-fifths).
The atmosphere is made up of approximately .......... nitrogen and .......... oxygen, with small amounts of other gases such as carbon dioxide and water vapour.
The atmosphere is made up of approximately 80% nitrogen and 20% oxygen, with small amounts of other gases such as carbon dioxide and water vapour.
How can burning phosphorus be used to find the percentage of oxygen in air?
Burning phosphorus can determine the percentage of oxygen because it burns inside a bell jar sitting in a trough of water, using up the available oxygen. As the oxygen is consumed, the water level rises inside the jar. Careful measurements of water levels before and after allow the percentage to be calculated.
Why is phosphorus a suitable substance for finding the percentage of oxygen in air?
Phosphorus is suitable because it burns readily in air and continues to burn until all the available oxygen is used up. This ensures an accurate measurement of the oxygen removed.
True or False?
Phosphorus is considered safe to handle and has no significant hazards.
False.
Phosphorus is toxic, so it is hazardous and must be handled with great care.
Gases in the atmosphere and their approximate percentages:
Gas
Approximate %
Nitrogen
Oxygen
Carbon dioxide, water vapour, noble gases
Gases in the atmosphere and their approximate percentages:
Gas
Approximate %
Nitrogen
~80%
Oxygen
~20%
Carbon dioxide, water vapour, noble gases
small/trace amounts
How does the water level inside a bell jar change when phosphorus burns in air, and why?
The water level rises inside the bell jar. This is because the burning phosphorus uses up the oxygen, reducing the volume of gas inside the jar.
What is the aim of this practical?
The aim is to determine the percentage of oxygen in air using the oxidation of iron (iron filings or iron wool).
In the burette practical, iron filings are placed inside an inverted burette in a trough of water. After 3-4 days, the water level .......... because the iron has .......... (reacted with) the oxygen.
In the burette practical, iron filings are placed inside an inverted burette in a trough of water. After 3-4 days, the water level rises because the iron has oxidised (reacted with) the oxygen.
How is the percentage of oxygen in air calculated from the burette experiment?
The percentage of oxygen is calculated by finding the initial volume of air and the final volume of air (after oxygen is removed). Volume of oxygen = initial volume − final volume. Percentage = (volume of oxygen ÷ initial volume) × 100.
True or False?
The water level in the burette rises after 3-4 days because oxygen has been used up by the rusting iron.
True.
Iron undergoes oxidation (rusting), reacting with the oxygen in the air inside the burette and causing the water level to rise.
Why must you wait 3-4 days before recording the final water level in the burette experiment?
You must wait 3-4 days because the iron takes time to fully oxidise (rust) and use up all the available oxygen in the burette. Reading too early would give an incomplete result.

Gas	Approximate %
Nitrogen
Oxygen
Carbon dioxide, water vapour, noble gases

Gas	Approximate %
Nitrogen	~80%
Oxygen	~20%
Carbon dioxide, water vapour, noble gases	small/trace amounts

Using the example data below, complete the calculation table:

Measurement	Value (mL)
Volume between 50 mL mark and tap	3.8
Initial water level	2.6
Final water level	12.7
Initial volume of air
Final volume of air
Volume of oxygen

Measurement	Value (mL)
Volume between 50 mL mark and tap	3.8
Initial water level	2.6
Final water level	12.7
Initial volume of air	(50.0 + 3.8) − 2.6 = 51.2
Final volume of air	53.8 − 12.7 = 41.1
Volume of oxygen	51.2 − 41.1 = 10.1

Define combustion.
Combustion is the scientific word for burning. It is a chemical reaction in which oxygen reacts with elements or compounds to produce oxides.
Why are combustion reactions always exothermic?
Combustion reactions always give out heat to the surroundings, making them exothermic.
True or False?
Combustion reactions can be classified as oxidation reactions.
True.
Combustion always involves reaction with oxygen, which means the substances are being oxidised. Combustion is therefore a type of oxidation reaction.
Complete the table of observations for the combustion of elements:
Element
Observation during combustion
Magnesium
Hydrogen
Sulfur
Element
Observation during combustion
Magnesium
Intense white flame; white powder (magnesium oxide) produced
Hydrogen
Exothermic; water produced
Sulfur
Blue flame; colourless, poisonous gas produced
What product is formed when sulfur burns in oxygen?
When sulfur burns in oxygen, sulfur dioxide (SO₂) is formed. It is a colourless, poisonous gas.
What are the products when magnesium burns in oxygen, and what observation is made?
Burning magnesium produces magnesium oxide (MgO), a white powder. The reaction produces an intense white flame.
True or False?
Water is produced when hydrogen burns in oxygen.
True.
When hydrogen burns in oxygen, the product is water (H₂O). The equation is: 2H₂ (g) + O₂ (g) → 2H₂O (g).
What is the symbol equation for the combustion of magnesium?
The equation is: 2Mg (s) + O₂ (g) → 2MgO (s)
When sulfur burns in oxygen, a .......... flame is produced and the gas .......... is formed, which is colourless and poisonous.
When sulfur burns in oxygen, a blue flame is produced and the gas sulfur dioxide (SO₂) is formed, which is colourless and poisonous.
Define thermal decomposition.
Thermal decomposition is a reaction in which a substance breaks down due to the action of heat.
What are the products of the thermal decomposition of a metal carbonate?
The products of thermal decomposition of a metal carbonate are a metal oxide and carbon dioxide gas.
When copper(II) carbonate is heated, it decomposes to form .......... and ...........
When copper(II) carbonate is heated, it decomposes to form copper(II) oxide and carbon dioxide.
True or False?
Copper(II) carbonate is a black powder that turns green when heated.
False.
Copper(II) carbonate is a green powder. When heated, it slowly darkens as black copper(II) oxide is produced.
How can you test that carbon dioxide gas has been produced in the thermal decomposition of copper(II) carbonate?
To test for carbon dioxide, pass the gas through limewater. If carbon dioxide is present, the limewater turns milky (cloudy).
What is the word equation for the thermal decomposition of copper(II) carbonate?
The word equation is: copper(II) carbonate → copper(II) oxide + carbon dioxide
True or False?
The release of carbon dioxide from calcium carbonate in cement production contributes to rising atmospheric CO₂ levels.
True.
The release of carbon dioxide from calcium carbonate in cement production is a contributing source of increased atmospheric CO₂, which contributes to the enhanced greenhouse effect.

Element	Observation during combustion
Magnesium
Hydrogen
Sulfur

Element	Observation during combustion
Magnesium	Intense white flame; white powder (magnesium oxide) produced
Hydrogen	Exothermic; water produced
Sulfur	Blue flame; colourless, poisonous gas produced

Complete the table for the thermal decomposition of copper(II) carbonate:

	Details
Starting material	Copper(II) carbonate
Colour of starting material
Products
Colour change observed
Test for gas produced

	Details
Starting material	Copper(II) carbonate
Colour of starting material	Green
Products	Copper(II) oxide and carbon dioxide
Colour change observed	Green to black (as copper(II) oxide forms)
Test for gas produced	Limewater turns milky

What is the greenhouse effect?
The greenhouse effect is the process by which greenhouse gases in the atmosphere trap heat energy, keeping the Earth's surface warm enough to support life.
What happens to short wavelength radiation from the Sun when it reaches Earth?
Short wavelength ultraviolet radiation from the Sun strikes the Earth's surface. Some is absorbed by the surface, and some is re-emitted as long wavelength infrared radiation.
True or False?
Greenhouse gases trap long wavelength infrared radiation in the atmosphere.
True.
Greenhouse gases absorb and store infrared (long wavelength) radiation re-emitted from the Earth's surface, trapping heat in the atmosphere.
The Sun emits .......... wavelength radiation. When this strikes the Earth's surface, some is re-emitted as .......... wavelength radiation, which is trapped by .......... gases.
The Sun emits short wavelength radiation. When this strikes the Earth's surface, some is re-emitted as long wavelength radiation, which is trapped by greenhouse gases.
Name the three main greenhouse gases.
The three main greenhouse gases are:
1. Carbon dioxide
2. Methane
3. Water vapour
How do increasing levels of carbon dioxide and methane affect the greenhouse effect?
Increasing levels of carbon dioxide and methane trap extra heat energy in the atmosphere, even though they are present in small amounts. This contributes to global warming.
True or False?
Without any greenhouse gases, the Earth's surface temperature would be stable and comfortable.
False.
Without greenhouse gases, the Earth's surface would swing between extreme heat and extreme cold. Greenhouse gases maintain a mean global temperature of around 15°C.
What is the difference between the greenhouse effect and the enhanced greenhouse effect?
The greenhouse effect is the natural process that keeps Earth's mean temperature around 15°C. The enhanced greenhouse effect is caused by increased greenhouse gas concentrations, which most scientists believe is leading to global warming.

Complete the table about the greenhouse effect:

Feature	Detail
Type of radiation emitted by Sun
Type of radiation re-emitted by Earth's surface
Gases that trap this radiation
Effect on Earth's temperature

Feature	Detail
Type of radiation emitted by Sun	Short wavelength (ultraviolet)
Type of radiation re-emitted by Earth's surface	Long wavelength (infrared)
Gases that trap this radiation	Greenhouse gases (e.g. CO₂, methane, water vapour)
Effect on Earth's temperature	Temperature is kept high enough to support life

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