gases

Question 1

2:09 know the approximate percentages by volume of the four most abundant gases in dry air

Answer 1

Nitrogen, N2

78.1

Oxygen, O2

21.0

Argon, Ar

0.9

Carbon dioxide, CO2

0.04

Question 2

2:11 describe the combustion of elements in oxygen, including magnesium, hydrogen and sulfur

Answer 2

Magnesium - reacts with oxygen producing a bright white flame leaving behind a white ash of magnesium oxide.

Hydrogen - reacts with oxygen in an explosive reaction. This is the basis of the ‘squeak pop’ test for hydrogen in test tube. With larger quantities of hydrogen this explosion can be dangerous.

Sulfur - reacts with oxygen producing a blue flame.

Question 3

2:12 describe the formation of carbon dioxide from the thermal decomposition of metal carbonates, including copper(II) carbonate

Answer 3

thermal decomposition - the process of breaking down by heating.

heating metal carbonates thermally decomposes them into metal oxides and carbon dioxide.

Copper carbonate -> copper oxide + carbon dioxide

Observation: green powder (CuCO3) changes to a black powder (CuO)

Question 4

2:10 understand how to determine the percentage by volume of oxygen in air using experiments involving the reactions of metals (e.g. iron) and non-metals (e.g. phosphorus) with air

Answer 4

Copper:

Put copper fillings in a tube between 2 gas syringes filled with air

Put a Bunsen burner underneath the copper to heat it

Put air back and forth between the copper until it turns black

Decreasing volume of air in the gas syringes is the oxygen being lost to combustion of copper

Phosphorus:

Add Phosphorus into an evaporating dish and place it on a trough of Water

Ignite Phosphorus using a candle

Cover evaporating dish with a bell jar

Measure and note the starting height of the Water level in the bell jar

Leave apparatus for several days

Measure and note the final height of the Water level in the bell jar

Rising water levels will replace oxygen lost during the reaction, and a constant level will be reached as Phosphorus uses up oxygen in the air to burn

Iron:

Add wet iron fillings into a conical flask with a bung and a tube going to an air syringe

Measure and note the starting level of air in the gas syringe

Leave apparatus for several days

Measure and note final level of air in the gas syringe

Decreasing air in gas syringe shows how oxygen is used up in the oxidization of iron