In this explainer, we will learn how to prepare oxygen gas and test some of its properties.
Oxygen is all around us. It is in the air we breathe, the water we drink, and the food we eat.
We have already learned that oxygen gas is one of the main components of Earth’s atmosphere. Earth’s atmosphere is a mixture of gases that surround Earth. Oxygen makes up of the volume of the atmosphere, as shown below.
To learn more about oxygen gas and its properties, we can prepare (make) it in the laboratory and perform some experiments.
Oxygen can be prepared in a laboratory from a liquid called hydrogen peroxide.
When hydrogen peroxide is broken down in the presence of a black powder called manganese dioxide, new substances (products) are formed.
This is an example of a decomposition reaction.
Definition: Decomposition Reaction
A decomposition reaction is a chemical reaction in which a substance dissociates (breaks down) into two or more products.
One of the products made when hydrogen peroxide breaks down is oxygen. The other product is water.
We can show this in an equation.
Equation: The Decomposition of Hydrogen Peroxide
The experiment can be carried out in the laboratory using the equipment and steps shown below.
Example 1: Identifying the Products in the Decomposition of Hydrogen Peroxide
When hydrogen peroxide decomposes in the presence of manganese dioxide, oxygen is formed:
What is the other product of this reaction?
When hydrogen peroxide decomposes in the presence of manganese dioxide, two products (new substances) are formed. One of these is oxygen, and the other is water.
So, the correct answer is water; it is the other product of the reaction.
In the preparation of oxygen, manganese dioxide acts as a catalyst.
A catalyst is a substance whose quantity and structure do not change during a chemical reaction. Catalysts speed up a chemical reaction.
Example 2: Applying the Definition of Catalyst
Manganese dioxide is a catalyst used in the preparation of oxygen from hydrogen peroxide.
What happens to manganese dioxide in this reaction?
- It disappears.
- It is used up.
- It does not change in quantity or in structure.
- It changes its structure.
- It gets bigger.
We know that manganese dioxide is a catalyst.
We also know that a catalyst is a substance whose quantity and structure do not change during a chemical reaction.
Options A, B, D, and E all describe changes in quantity or structure. Since catalysts do not change in quantity or structure, these options must be incorrect.
So, the correct answer is option C; manganese dioxide does not change in quantity or structure when used in the preparation of oxygen from hydrogen peroxide.
Having collected oxygen gas, we can investigate its properties.
Look at this jar. It may look empty, but in fact, it contains oxygen gas.
We can see that the oxygen gas has no color. It is invisible.
If we tried to smell and taste the oxygen gas, we would find that oxygen gas has no taste or smell.
Properties: The Color, Taste, and Odor of Oxygen Gas
Oxygen gas is colorless, tasteless, and odorless.
Example 3: Identifying the Color and Odor of Oxygen Gas
Amira observed 4 different gases in glass cylinders.
|Gas||Is It Colored?||Does It Have an Odor?|
Using the information in the table about color and odor, which gas could be oxygen?
Oxygen has no color and no odor.
Gas 1 has color and odor, so it cannot be oxygen gas.
Gas 2 has color, so it cannot be oxygen gas.
Gas 3 has odor, so it cannot be oxygen gas.
The only gas in the table that is not colored and has no odor is gas 4.
So, the correct answer is gas 4.
We also can test if oxygen gas is soluble (dissolves) in water by placing a cylinder of gaseous oxygen upside down in water.
We can then observe the level of the water in the cylinder:
- If oxygen dissolves in the water, the water level rises, as the volume of oxygen gas decreases.
- If the oxygen does not dissolve in the water, the water level will stay the same.
When we do this experiment, the water level rises only a small amount. This tells us that gaseous oxygen scarcely dissolves in water.
Property: The Solubility of Oxygen Gas in Water
Oxygen gas scarcely dissolves in water.
Look back at how we prepare oxygen from the decomposition of hydrogen peroxide. Notice that we collect oxygen gas over water.
Collecting oxygen in this way would not be possible if oxygen dissolved easily in water.
Example 4: Identifying the Solubility of Oxygen Gas in Water
Fady and Lobna are talking about the oxygen produced when hydrogen peroxide decomposes.
Who is correct?
When we prepare oxygen from the decomposition of hydrogen peroxide, we collect it over water. The oxygen displaces the water in the cylinder.
This would not be possible if oxygen dissolved in water. Oxygen is scarcely soluble in water.
Therefore, Fady is incorrect and only Lobna is correct. Oxygen does not dissolve in water, but it does displace water.
So, only Lobna is correct.
We can investigate how heavy oxygen is compared to air using these steps:
- Turn a beaker filled with oxygen upside down on top of a beaker that contains air to mix their contents, as shown in the image below.
- Wait for a minute.
- Insert a burning match into the upper beaker.
- Insert a burning match into the lower beaker.
When we do this, we see that the match glows more strongly in the lower beaker.
Oxygen helps with burning. The presence of oxygen makes a match glow brighter.
So, the match glowing strongly tells us that there is more oxygen in the lower beaker.
Oxygen fell to the lower beaker because it is heavier than air.
Property: The Weight of Oxygen Gas Compared to Air
Oxygen gas is heavier than air.
Example 5: Identifying the Weight of Oxygen Compared to Air
The mass of oxygen compared to air can be investigated in a laboratory.
Fill in the blanks: After one minute, all of the oxygen will be in because it is than air.
- beaker 1, heavier
- beaker 2, lighter
- beaker 1, lighter
- beaker 2, heavier
We know that oxygen gas is heavier than air.
When two gases are mixed, the heavier gas will fall to the bottom.
Therefore, when oxygen and air are mixed, oxygen will fall to the bottom.
Since beaker 2 is below beaker 1, oxygen, the heavier gas, will fall into beaker 2.
So, the answer is option D; after one minute, all of the oxygen will be in beaker 2 because it is heavier than air.
In this explainer, we have learned how to prepare oxygen gas and test some of its properties.
Let’s recap the key points.
- Oxygen can be prepared from the decomposition of hydrogen peroxide:
- Manganese dioxide is the catalyst in this reaction.
- A catalyst is a substance whose quantity and structure do not change during a chemical reaction. Catalysts speed up a chemical reaction.
- is colorless, tasteless, and odorless,
- scarcely dissolves in water,
- is heavier than air.