Other gases: 1% (mainly Argon (Ar), traces of other noble gases, and Carbon Dioxide (CO₂) at 400 ppm or 0.04%)
Discovery of Oxygen
Space Shuttle Oxygen Supply:
Question about how space shuttles carry their oxygen supply.
Liquid Oxygen Transport:
Question about why oxygen is transported as a liquid.
Mercury Heated in Air:
Question about what happens to mercury when heated in air.
Priestley's Observation:
Question about what Priestley thought was given off when substances burned in oxygen.
Lavoisier's Experiment:
Question about which non-metallic element Lavoisier first burned in air to test his oxygen theory.
Magnesium Heating:
Question about what happens to the mass of a piece of magnesium after strong heating in air.
Scheele's Method:
Question about what type of compound Scheele heated to collect oxygen gas.
Modern Uses of Oxygen:
Question about two modern uses for oxygen.
Key Scientists:
Question about naming the three key scientists and their nationalities in the discovery of oxygen.
Experiment OXID/1: Determining the Percentage of Oxygen in Air
Apparatus:
Two gas syringes connected to a glass tube containing excess copper granules.
Total initial volume of air in both syringes: 100 cm^3.
Procedure:
Air is passed over heated copper in a Bunsen flame.
The volume of gas is measured after no further change is observed and the apparatus has cooled.
Measurements:
Initial volume of air: 100 cm^3
Final volume of air: to be recorded
Volume decrease: to be calculated
Calculations:
Percentage of oxygen in air: Calculated using the volume decrease.
Questions:
Ensuring unreacted copper: Why it's important to have some unreacted copper left over at the end of the reaction (Correct option: C - So that we know that all the Oxygen has been used up).
Cooling the apparatus: Why it's important to let the apparatus cool before measuring the final volume (Correct option: C - Because the hot gas expands and will make the readings on the syringe appear larger than they should).
Replacing copper with magnesium: Why this experiment wouldn't work if copper were replaced with magnesium (Correct option: B - Magnesium will also react with nitrogen and not just oxygen).
Experiment OXID/2: Percentage of Air Used Up When Iron Rusts
Process:
Iron rusts, removing oxygen from the air.
Steel wool is placed in a measuring cylinder, soaked in water, and inverted over a beaker of water.
The setup is left for a week to allow the iron to rust.
Measurements:
Initial volume of air: to be recorded in cm^3
Final volume of air: to be recorded in cm^3
Volume of air used up: to be calculated in cm^3
Percentage of oxygen in air: to be calculated
Phosphorus Experiment:
Phosphorus reacts with oxygen in the air, forming solid phosphorus oxide (P4O{10}).
This reduces the pressure, causing the water level in a bell jar to rise by about 20%.
Reaction: phosphorus + oxygen → phosphorus oxide
Experiment OXID/4: Reactions of Elements with Oxygen
Test for oxygen gas: Described.
Process:
Elements react with oxygen to form oxides.
A sample of the element is heated in a strong flame and transferred to a gas jar containing oxygen.
Distilled water is added to the gas jar to dissolve any oxide produced.
Universal indicator is added to the solution to determine the pH.
Results Table:
Elements tested: Carbon, Sodium, Sulfur, Magnesium.
Observations: To be recorded for each element.
Color and pH of solution: To be recorded for each element.
Observations:
Note differences between oxides formed by metals and non-metals.
Balanced Equations:
Write balanced equations for the reactions between sodium, sulphur, magnesium, and carbon, including state symbols.
Experiment HYD/2: Combustion of Hydrogen
Apparatus:
Draw a neat labeled diagram of the apparatus used in this experiment.
Observations:
Describe the appearance of the liquid that collects in the test-tube.
Describe how the liquid is tested and the result of the test.
Explain whether this test proves that the liquid is pure.
How to use a physical test to show that the liquid is pure water.
Greenhouse Gases
Greenhouse Gases:
Name at least two gases that can be described as greenhouse gases.
Explain how these gases are produced.
Effect on Climate:
What effect does the build-up of greenhouse gases have on the world's climate?
Polar Ice Caps:
Given that polar ice caps contain a significant amount of dissolved carbon dioxide and methane, what are the potential problems of polar ice caps melting?
Experiment OXID/6: Thermal Decomposition of Copper(II) Carbonate
Procedure:
A test-tube with approximately 0.4g of copper(II) carbonate is pre-weighed.
The tube is connected to a gas syringe.
The test-tube is heated until the copper carbonate has completely decomposed.
The apparatus is allowed to cool, and the volume of gas given off is measured.
The mass of the test-tube + solid after heating is reweighed.
Measurements and Calculations:
Mass of test-tube + copper carbonate before heating: to be recorded in grams (g).
Volume of gas given off: to be recorded in cubic centimeters (cm^3).
Mass of test-tube + solid after heating: to be recorded in grams (g).
Mass loss in the reaction: to be calculated in grams (g).
Mass of the gas given off in the reaction: to be calculated in grams (g).
Density of the gas (mass/volume): to be calculated in g/cm^3.
Gas Identification:
Density of gases provided: Oxygen (0.0013 g/cm^3), Carbon dioxide (0.0018 g/cm^3), Carbon monoxide (0.0012 g/cm^3).
Identify the gas from the densities.
Solid Residue:
What is the solid remaining in the test-tube?
Equations:
Write a word equation for the reaction that has occurred.
Write a balanced symbol equation for the reaction that has occurred.
Confirmation:
Heat a fresh sample of copper(II) carbonate and test the gas produced with limewater.
Observe if the limewater turns cloudy.
Observations Table:
Substance: Copper(II) carbonate, Lime water.
Observations: Before reaction, After reaction.
Questions:
Evidence of a chemical reaction: Give two pieces of evidence.
Gas produced: Which gas is produced in the reaction?