The word ʻdisplacementʼ as it is used here means that the gas produced pushes air out of the jar and takes its place.
Be careful though, ʻdisplacementʼ has a different meaning elsewhere in the science world. See Physical World 17.1 for another use of the word.
Collecting gases
The density of oxygen is roughly the same as the density of air. The density of carbon dioxide is greater than the density of air. Which methods outlined above would be suitable for collecting oxygen and carbon dioxide gases? Explain your answers.
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Method 1: downward displacement of air
z zz Fig. 12.5.1 Methods for collecting gas
Method 1 can be used for a gas that is heavier (more dense) than air. The gas produced sinks to the bottom of the flask and air is pushed out the top as the flask is filled with the gas.
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Method 2 can be used for a gas that is lighter (less dense) than air. The gas produced moves to the top of the flask and air is pushed out of the flask as the flask fills with the gas.
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Method 3 can be used to collect gases that do not dissolve in water. You will easily see when the jar is full of the new gas as there will be no water left in the jar.
Production of Oxygen Gas
Oxygen is prepared in the laboratory by breaking the chemical bonds in hydrogen peroxide molecules. Hydrogen peroxide will break up into water and oxygen gas. The word equation for this reaction is:
Hydrogen peroxide → water + oxygen gas
The breakdown of hydrogen peroxide into water and oxygen gas is a decomposition reaction. In a decomposition reaction, a substance breaks down into simpler substances.
Method 2: upward
displacement of air
Production of Gases Learning Intentions
In this topic we are learning to: zz
zz zz Produce and test for the presence of oxygen and carbon dioxide gases.
Design an investigation to verify that surface area and particle size affect the rate of a reaction.
Investigate how the presence of a catalyst affects the rate of reaction.
When producing a gas, there are three ways the gas can be collected: Gas jar
