Gases in the atmosphere

Question 1

What are the approximate percentages by volume of the four most abundant gases in dry air?

Answer 1

78% Nitrogen, 21% Oxygen, 0.9% Argon, 0.037% Carbon Dioxide

Question 2

How can you determine the percentage by volume of oxygen in the air using experiments? Provide an example

Answer 2

• divide the change in the burette reading by the original volume of air in the burette and multiply by 100.
• The water level in the burette will rise because the iron filings react with the oxygen in the burette.

Question 3

Describe the combustion of magnesium in oxygen.

Answer 3

• results in an intense white flame, producing white powder (magnesium oxide).

Question 4

What are the observations during the combustion of hydrogen in oxygen?

Answer 4

• Hydrogen combustion is exothermic, producing water.

Question 5

Describe the combustion of sulfur in oxygen.

Answer 5

• results in a blue flame, with colorless, poisonous gas produced.

Question 6

How does copper(II) carbonate decompose, and what is the observable change?

Answer 6

• decomposes into copper oxide and carbon dioxide. It appears as a green powder and darkens as black copper(II) oxide forms.

Question 7

Explain the greenhouse gas effect and its relation to climate change.

Answer 7

• The greenhouse gas effect involves the absorption of infrared radiation by gases like CO2, leading to warming.
• This enhanced greenhouse effect contributes to global warming and climate change due to increased average global temperatures.

Question 8

A piece of copper is heated in air.

State the formula and color of the compound formed.

Answer 8

Formula: CuO

Colour: Black

Question 9

Identify the acid formed when sulfur dioxide reacts with water.

Answer 9

Sulfuric (IV) acid

Question 10

Identify another pollutant gas that forms acid rain

Answer 10

Nitrogen dioxide

Question 11

State two problems caused by acid rain

Answer 11

• Damages the trees
• damages marine life

Question 12

Why is it necessary to lift the lid from time to time while heating?

Answer 12

• to allow air

Question 13

Why is it necessary to repeat the heating until two consecutive masses are the same?

Answer 13

• to make sure that all of the magnesium has reacted

Question 14

Show how the mass of magnesium oxide formed can be calculated from the readings obtained

Answer 14

Mass of crucible (and lid) + MgO - mass of crucible (and lid)

Question 15

Why is the gas allowed to cool before its volume is measured?

Answer 15

• Gas evaporates when heated

Question 16

Suggest why the small pile of copper does not turn black

Answer 16

All of the oxygen has been used up.

Question 17

Describe how sulfur dioxide has caused this change in appearance

Answer 17

• Sulfur dioxide reacts with acid rain to form an acidic solution which reacts with the marble

Question 18

Explain why the copper turns black

Answer 18

The copper oxidizes to form copper(II) oxide

Question 19

Give the name of the gas that makes up most of the remaining 0.96% of the air

Answer 19

Argon

Question 20

State use for Nitrogen

Answer 20

Food packaging

Question 21

From this measurement, how could she tell whether all of the oxygen in the test tube had been used up in the first week?

Answer 21

The height is the same as before

Question 22

Suggest why the reaction between titanium chloride and magnesium cannot be successfully carried out in an atmosphere of air

Answer 22

Titanium reacts with oxygen

Question 23

Suggest why the mixture is crushed into a powder before it is added to water

Answer 23

Magnesium chloride will dissolve more quickly

Question 24

How is the carbon monoxide in the exhaust fumes produced?

Answer 24

Incomplete combustion of the octane