Oxygen, Oxides And CO2 (T2)

Question 0

Why is oxygen essential for combustion to take place?

Answer 0

Oxygen is extremely reactive.

It is essential for combustion as burning is a reaction with oxygen, so without it burning would not happen at all.

If we set fire to elements, they will react with the oxygen in the air to create oxides.

Question 1

Describe what makes up the air we breathe..

Answer 1

In the air we breathe, the amount of oxygen present is about 1/5.

The bulk is nitrogen, although as nitrogen is largely inert for us, when you breathe in only 1 in 5 parts of the gas is used by the body.

Carbon dioxide and water are present but in such small quantities if we made “dry air” with all carbon dioxide removed, the air can be liquified at low temperatures, and if fractionally distilled, oxygen and nitrogen would be the only products present. This goes for neon and argon too.

Nitrogen - 78%
Oxygen - 21%
Argon - almost 1%
Carbon dioxide - 0.03%
Neon - 0.002%

Question 2

Describe “oxides”…

Answer 2

If we set fire to elements they will react with the oxygen in the air to create oxides,

Oxides are a form of an element with an oxygen atom joined onto it.

If an element reacts with oxygen during combustion, it is undergoing an ‘oxidation reaction’.

Oxygen is being added to it.

Question 3

What happens when magnesium reacts with oxygen?

Answer 3

Magnesium oxide is formed.

Magnesium + oxygen -> magnesium oxide

2Mg + O2 -> 2MgO2

Question 4

If oxygen is already part of a compound, explain what kind of reaction can happen and give an example of when this may be useful…

Answer 4

If oxygen is already part of a compound, a ‘reduction reaction’ is possible.

This can be useful for refining metals since more metallic ores are found as oxides.

Eg:

Iron oxide + carbon -> iron + carbon dioxide

2Fe2O3 + 3C -> 4Fe + 3CO2

Question 5

Describe combustion..

Answer 5

• combustion is really focused around a chemical reaction with oxygen
• as material is heated it approaches a threshold where the atoms have enough energy to react
• this energy is needed to break the chemical bonds between atoms and cause the reaction
• the threshold is often based around temperature

Question 6

In reactions with metals, what pH will the oxides formed have?

Answer 6

They will be alkaline or base.

Question 7

When oxygen reacts with non-metals, how is the reaction and result different to the reaction with metals?

Answer 7

• with non metals, the reactions tend to be less violent and short lived
• the binding creates an acidic solution which will mix with water
• this is part of the problem with both carbon and sulphur in terms of pollution

Question 8

What is an “amphoteric oxide”?

Answer 8

An oxide that can react as an acid or a base.

These are very rare.

Question 9

Describe an experiment to measure oxygen in the air..

Answer 9

Oxygen in the air can be measured by passing a known volume of air over hot copper and measuring the decrease in volume as the oxygen reacts with it.

Copper + oxygen -> copper oxide

2Cu + O2 -> 2CuO

Gas syringes containing air are attached to a tube with some copper turnings, suspended above a lit Bunsen burner.

To make analysis easy, the starting volume of air is often 100 cm 3.

If this case the final calculations should be..

Volume at start: 100 cm 3
Volume at end: 79 cm 3
Volume of oxygen: 100-79 = 21 cm 3
% of oxygen in the air = 21 x 100 / 100 = 21%

NOTE:

There is some air in the tube with the copper turnings which will also react with the hot copper, causing a small error in the final volume recorded

You must let the apparatus cool down at the end of the experiment or the final reading will be too high

Question 10

As well as copper, what other elements can be used in a lab experiment to measure the amount of oxygen in the air?

Answer 10

Iron and phosphorus can also be used as they bind with oxygen to make an oxide when heated..

Question 11

How would you CREATE pure oxygen as opposed to remove it?

Answer 11

1) some manganese dioxide (MnO2) and water (H2O) are taken in a conical flask with a thistle funnel running into it, and a delivery tube running out of it
2) hydrogen peroxide (H2O2) is added drop by drop down the thistle funnel
3) the oxygen gas escapes via the delivery tube, which leads into a trough of water with a beehive shelf and gas jar attached to it
4) the oxygen gas is collected in the gas jar with the downward displacement of water

2H2O2 -> 2H2O + O2

Hydrogen peroxide -> water + oxygen

NOTE: the MnO2 is used as a catalyst as it speeds up the reaction without actually being used in the reaction

Question 12

How would you produce carbon dioxide in a lab by use of calcium carbonate and HCl?

Answer 12

CaCO3 + HCl -> CaCl2 + H2O +CO2

1) some pieces of calcium carbonate are out in a round bottom flask which is fixed to a clamp with a thistle funnel running into it and a delivery tube running out of it into a gas jar
2) hydrochloric acid is added to it until the carbon dioxide evolves
3) the CO2 travels up and along the delivery tube and is collected in the gas jar by the upward displacement of air

Question 13

How could we produce carbon dioxide by use of copper II carbonate (or any metal carbonate)?

Answer 13

1) put some copper II carbonate in a round bottom flask with a delivery tube attached to it, leading to a gas jar
2) heat the flask up with a Bunsen burner
3) the CO2 travels up and along the delivery tube and is collected in the gas jar by the upward displacement of air

Question 14

What is thermal decomposition?

Answer 14

The breaking down of a chemical compound through heating

Question 15

Give a couple of examples of chemicals reacting with oxygen to make up pollutants..

Answer 15

• sulphur dioxide and nitrogen dioxide form acids during oxidation, leading to acid rain
• carbon monoxide is produced during incomplete burning of some fuels

Question 16

What is a reduction reaction?

Answer 16

To obtain metal from an oxide you have to remove the oxygen. This process is called ‘reduction’.

Metals exist as positive ions in their ionic compounds and to produce the metal you would add electrons to the positive ion. This addition of electrons is also known as ‘reduction’.