Oxygen and oxides

Question 1

What percentage of oxygen is in unpolluted dry air?

Answer 1

21%

Question 2

What percentage of nitrogen is in unpolluted dry air?

Answer 2

78.1

Question 3

What percentage of argon is in unpolluted dry air?

Answer 3

0.9

Question 4

What percentage of carbon dioxide is in unpolluted dry air?

Answer 4

0.04

Question 5

What percentage of other noble gases is in unpolluted dry air?

Answer 5

tiny percentages

Question 6

Describe an experiment to show the percentage of oxygen in air using copper:

Answer 6

• connect two gas syringes with a silicon tube packed with copper
• one gas syringes should be filled with 100cm3 of air between them. Push this back and forth over the copper as it is heated by a bunsen burner which turns into copper oxide
• ensure that the bunsen is moved along the tube so it heats different copper
• the volume of gas should fall as the oxygen is used up. Wait for it to cool and then work out how much oxygen has been used up.

Question 7

equation of this experiment?

an experiment to show the percentage of oxygen in air using copper

Answer 7

2Cu (s) + O2 (g) —> 2CuO (s)

Question 8

What colour is copper oxide?

Answer 8

Black

Question 9

How can you work out the percentage of oxygen in air from the experiment? (using copper)

Answer 9

When the copper stops turning black and the volume of gas in the syringes stops changing, on cooling there should be around 79cm3 of gas left in the syringes. This means 21% has been used up. Therefore the air contained 21% of oxygen.

Question 10

Why should you let the apparatus cool before working out the percentage?

Answer 10

When gas is heated it expands and so the readings could show to be higher than usual and therefore be inaccurate. The volume of the gas should be that at room temperature.

Question 11

When does iron rust?

Answer 11

When in contact with water and oxygen, it will use up the oxygen.

Question 12

Describe an experiment to show the percentage of oxygen in air using iron:

Answer 12

• place some damp iron wool in the bottom of a test tube.
• the tube is inverted in a beaker of water and the level of water in the tube is marked by a rubber band or permanent marker.
• leave the tube for a week or so for the iron to use up all the oxygen in rusting
• the water level rises in the tube as the oxygen is used up. Mark the new level with another plastic band.
• at the end of the experiment fill the tube with water to the level of each of the plastic bands and pouring it into a small measuring cylinder.
• If the original volume was, say, 15cm3 and the final was 12cm3 then the oxygen used up measured 3cm3.
The percentage of oxygen in the air was 3/15 x 100 = 20%

Question 13

Describe an experiment to make oxygen in a lab:

Answer 13

• place solid manganese oxide in a side arm boiling tube and place a delivery tube in a beaker of water.
• fill a test tube with water and place it above the delivery tube to collect the oxygen.
• add the hydrogen peroxide solution in a thistle funnel.

Question 14

What is this method of making oxygen called?

Answer 14

catalytic decomposition of hydrogen peroxide (splitting up hydrogen peroxide using a catalyst)

Question 15

equation for the catalytic decomposition of hydrogen peroxide:

Answer 15

2H2O2 (aq) —> 2H2O (l) + O2 (g)

Question 16

How can you test oxygen?

Answer 16

Oxygen relights a glowing splint

Question 17

Describe the burning of magnesium in oxygen:

Answer 17

Magnesium burns with a very bright white fame

Question 18

What does magnesium oxide look like?

Answer 18

A white, powdery ash

Question 19

Equation for burning magnesium in air:

Answer 19

2Mg (s) + O2 (g) —> 2MgO (s)

Question 20

Describe the burning of sulfur in oxygen:

Answer 20

Sulfur burns with a tiny, almost invisible, blue flame

but in OXYGEN it burns much more strongly giving a bright blue flame

Question 21

Equation for burning sulfur in air:

Answer 21

S (s) + O2 (g) —> SO2 (g)

Question 22

What is produced when you burn sulfur in air?

Answer 22

Sulfur dioxide, a colourless and poisonous gas

Question 23

Describe the burning of carbon in oxygen:

Answer 23

If it is heated very strongly carbon will burn in air or oxygen. It may produce a small yellow-orange flame and perhaps some sparks but this depends on the purity of the carbon.

Question 24

Equation for burning carbon in air:

Answer 24

C (s) + O2 (g) —> CO2 (g)

Question 25

What is produced when you burn carbon in air?

Answer 25

a colourless gas called carbon dioxide

Question 26

Are metal oxides soluble in water? Do they react with it?

Answer 26

Most metal oxides are not soluble in water and do not react with it.

Question 27

What will happen if you shake some solid magnesium oxide with water?

Answer 27

It doesn’t seem to dissolve but if you test the pH of the mixture you will see that it is slightly alkaline. A very, very small amount does react with the water, forming some magnesium hydroxide. A very small amount of that dissolves in the water making it slightly alkaline.

Question 28

Equation for reaction of magnesium oxide and water:

Answer 28

MgO (s) + H2O (l) —> Mg(OH)2 (s and aq)

Question 29

Do non-metal oxides react with it water? Example?

Answer 29

Many non-metal oxides react with water to give acidic solutions e.g. sulfur doxide reacts to give sulfurous acid

BUT not all do

Question 30

What non-metal oxides do not react with water to form acidic solutions?

Answer 30

common exceptions are water and carbon monoxide

Question 31

What causes acid rain?

Answer 31

Water and oxygen in the atmosphere reacting with sulfur dioxide to produce sulfuric acid or with various oxides of nitrogen to give nitric acid.

Question 32

Where do SO2 and NOx (various oxides of nitrogen) come from?

Answer 32

power stations and factories burning fossil fuels or from motor vehicles

Question 33

What is bad about acid rain?

Answer 33

Trees die or become sick.
Limestone buildings are damaged.
Lakes can become too acidic to support life.

Question 34

Describe the greenhouse effect:

Answer 34

Energy comes from the sun
This energy is re-emitted as infra-red radiation
Some IR energy is absorbed by molecules like carbon dioxide
Energy transferred by collisions to other molecules warms up the atmosphere

Question 35

What happens when carbon dioxide dissolves in water?

Answer 35

Carbon dioxide dissolves to some extent in water to give off carbonic acid (H2CO3)

Question 36

How can you test for carbon dixoide?

Answer 36

Carbon dioxide turns lime water (calcium hydroxide solution) milky.

Question 37

Properties of carbon dioxide:

4

Answer 37

colourless, odourless gas, denser than air, slightly soluble in water

Question 38

Uses of carbon dioxide (2):

Answer 38

Carbonated fizzy drinks because it dissolves in water under high pressure.
Fire extinguishers which are used to put out electrical fires or those caused by burning liquids where using water could create more problems. The dense gas sinks on the flames and prevents oxygen from reaching them.

Question 39

How would you go about making carbon dioxide in a lab?

What is the equation?

Answer 39

Reacting dilute hydrochloric acid and calcium carbonate (GREEN) in the form of marble chips.
CaCO3 (s) + 2HCl (aq) —> CaCl2 (aq) + CO2 (g) + H2O (l)