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Questions and Answers
What are the four most abundant gases in dry air?
What are the four most abundant gases in dry air?
What is the approximate percentage by volume of nitrogen in dry air?
What is the approximate percentage by volume of nitrogen in dry air?
78.1%
What is the approximate percentage by volume of carbon dioxide in dry air?
What is the approximate percentage by volume of carbon dioxide in dry air?
0.04%
Which of the following is NOT a method used to determine the percentage by volume of oxygen in air?
Which of the following is NOT a method used to determine the percentage by volume of oxygen in air?
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Elements burn more brightly and rapidly in pure oxygen than in air.
Elements burn more brightly and rapidly in pure oxygen than in air.
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Which of the following elements is NOT one of the three key combustion reactions you should know?
Which of the following elements is NOT one of the three key combustion reactions you should know?
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What is the chemical formula for magnesium oxide?
What is the chemical formula for magnesium oxide?
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What is the chemical formula for sulfur dioxide?
What is the chemical formula for sulfur dioxide?
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What is the chemical formula for water?
What is the chemical formula for water?
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Metal oxides are generally basic oxides.
Metal oxides are generally basic oxides.
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Non-metal oxides are generally acidic oxides.
Non-metal oxides are generally acidic oxides.
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Thermal decomposition is a process that involves breaking down a compound by heating.
Thermal decomposition is a process that involves breaking down a compound by heating.
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What is the chemical formula for copper(II) carbonate?
What is the chemical formula for copper(II) carbonate?
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What is the chemical formula for calcium carbonate?
What is the chemical formula for calcium carbonate?
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Carbon dioxide is a greenhouse gas.
Carbon dioxide is a greenhouse gas.
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The greenhouse effect is entirely caused by human activity.
The greenhouse effect is entirely caused by human activity.
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Which of the following is NOT a consequence of climate change?
Which of the following is NOT a consequence of climate change?
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Study Notes
IGCSE Science C2 Inorganic Chemistry 2C Gases in the Atmosphere (Double)
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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 the air using experiments involving the 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 approximate percentages (by volume) of the four most abundant gases in unpolluted, dry air are:
- 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 consists of other noble gases in very small amounts (helium, neon, krypton, xenon, and radon).
Measuring the Percentage of Oxygen - Practicals
- There are three key experiments used for measuring oxygen percentage:
- Using copper
- Using the rusting of iron
- Using phosphorus
- All methods rely on the reaction of a substance with oxygen in the air.
- The volume decrease is observed as oxygen is removed.
Using Copper - Apparatus
- Description: A diagram shows the apparatus, including a gas syringe, silica tube packed with copper filings, and the setup for measuring air volume.
- Equation: 2Cu(s) + O₂(g) → 2CuO(s)
- Observation: Pink-brown copper turns black as copper(II) oxide forms.
Using Copper - Method
- Steps outline the procedure for the copper experiment
- The steps include:
- Setting up the gas syringe apparatus to initially hold 100 cm³ of air.
- Heating the silica tube containing copper filings strongly using a Bunsen burner.
- Pushing the plungers of the syringes in sequence (left, then right).
- Periodically moving the Bunsen burner.
- Observing the volume decrease in the gas syringe.
- Cooling the apparatus, and recording the final reading.
Using Copper - Calculation
- Table of Results: A table displays initial and final air volumes to calculate oxygen volume.
- Step 1: Volume of Oxygen: 100 cm³ initial - 79 cm³ final = 21 cm³.
- Step 2: Percentage of Oxygen: (21 cm³ /100 cm³) * 100% = 21%.
Using Copper - Key Points
- Ensure all oxygen reacts (copper in excess).
- Cool the apparatus before the final reading (gases expand when hot).
- Readings too early may yield lower-than-expected oxygen percentages.
- Typical values are usually between 18% to 24%.
Using Rusting of Iron - Apparatus
- Description: A diagram illustrates the setup for the iron experiment, showing a conical flask containing wet iron fillings, a connecting tube, and a gas syringe.
- Equation: 4Fe(s) + 3O₂(g) + 6H₂O(l) → 4Fe(OH)₃(s)
- Observation: Black iron filings become red-brown with rust formation.
Using Rusting of Iron - Method
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Steps:
- Find the initial volume of air, measuring the air in the conical flask and connecting tube using water and a cylinder.
- Set up the apparatus according to the diagram.
- Put wet iron filings into the conical flask.
- Record the initial gas syringe reading.
- Leave the apparatus for a week, ensuring the final reading is stable.
- Record the final gas syringe reading.
Using Rusting of Iron - Calculation
- Total initial volume = Initial volumes of the conical flask, connecting tube, and syringe.
- Total final volume = Final reading on gas syringe.
- Volume of Oxygen = Total initial volume – Total final volume.
- Percentage of Oxygen = (volume of oxygen/ total volume) x 100%
Using Rusting of Iron - Key Points
- Include the volumes of all parts of the apparatus in the calculation.
- Ensure the iron is in excess.
- The experiment takes time (at least a week).
- Typical values are between 18% and 24%.
Using Phosphorus - Apparatus
- Description: A diagram shows an evaporating basin, a bell jar, a trough of water and Phosphorus inside.
- Equation: 4P(s) + 5O₂(g) → 2P₂O₅(g) .
- Observation: Phosphorus reacts with oxygen, forming phosphorus oxide; noticeable rising of the water level in the trough.
Using Phosphorus - Method
- Set up the apparatus.
- Mark the initial water level of the bell jar.
- Remove the bung and ignite the phosphorus.
- Replace the bung quickly.
- The water level rises as oxygen is consumed
- Mark the final water level.
- Measure the volume of water displaced.
Using Phosphorus - Calculation
- Initial Measurement: Initial volume of water in the bell jar.
- Final Measurement: Final volume of water in the bell jar.
- Volume Change: Calculate the difference between initial and final measurement. This represents the volume of oxygen consumed.
- Percentage of Oxygen: The volume of water displaced corresponds to consumed oxygen
Using Phosphorus - Key Points
- Ensure complete oxygen reaction (phosphorus in excess).
- For safety, this method is often conducted by a teacher.
- Similar experiment possible with candle, petri dish, and water cylinder.
- Typical values are usually between 18% to 24%.
Combustion of Elements in Oxygen
- Elements burn more brightly and rapidly in pure oxygen (100%) than they do in air (21% oxygen).
- Examples include magnesium, sulfur, and hydrogen.
- Combustion reactions (or sometimes oxidation reactions) are observed.
Combustion of Magnesium
- Magnesium (a silver ribbon) burns in oxygen to form magnesium oxide (a white powder).
- Equation: 2Mg(s) + O₂(g) → 2MgO(s)
- Magnesium oxide can dissolve in water to form magnesium hydroxide
Combustion of Sulfur
- Sulfur (a yellow powder) burns in oxygen to form sulfur dioxide (a colourless gas).
- Equation: S(s) + O₂(g) → SO₂(g)
- Sulfur dioxide dissolves in water to form sulfurous acid.
Combustion of Hydrogen
- Hydrogen (a colourless gas) burns in oxygen to form water (a colourless liquid).
- Equation: 2H₂(g) + O₂(g) → 2H₂O(l) The reaction can explode if ignited
Properties of Oxides
- Metal Oxides: Ionic compounds, basic oxides, typically insoluble in water, form alkaline solutions with hydroxide ions (OH-).
- Non-metal Oxides: Covalent compounds, acidic oxides, often soluble in water, forming acidic solutions with hydrogen ions (H+).
Thermal Decomposition
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Carbon dioxide is formed from the decomposition of metal carbonates (e.g., copper carbonate or calcium carbonate).
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Thermal decomposition is heating to cause a substance to break down.
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Copper Carbonate: A green powder that decomposes on heating into black copper(II) oxide and carbon dioxide gas.
- Equation: CuCO₃(s) → CuO(s) + CO₂(g)
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Calcium Carbonate: Decomposes at high temperatures, forming calcium oxide and carbon dioxide gas.
- Equation: CaCO₃(s) → CaO(s) + CO₂(g)
The Greenhouse Effect
- Carbon dioxide is a greenhouse gas.
- The greenhouse effect happens when high-energy UV and visible light warm Earth.
- Trapped heat from the atmosphere leads to further warming (greenhouse effect).
- Increasing CO2 levels contribute to climate change, leading to effects such as melting polar ice caps, rising sea levels, and extreme weather patterns (floods, droughts, heat waves).
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Description
This quiz focuses on the composition of gases in the atmosphere as part of the IGCSE Science syllabus. Students will learn about the approximate percentages of gases in dry air, the combustion processes, and the impact of greenhouse gases like carbon dioxide. Engage in practical experiments to understand the volume of oxygen in the air and its significance.
