Oxygen and oxides
2.16 recall the gases present in air and
their approximate percentage by
volume
Air is a mixture of gases
which contains 4/5 nitrogen
1/5 oxygen
2.17 describe how experiments involving the reactions of elements such as
copper, iron and phosphorus with air can be used to determine the
percentage by volume of oxygen in air
• Experiment with copper
• This can be demonstrated by the reaction
of a fixed amount of air with heated copper.
Copper will react with oxygen in the air to
form copper(II) oxide.
• copper + oxygen  copper(II) oxide.
2Cu(s) + O2(g)
2CuO(s)
• A known amount of air is passed backward and
forward
over the heated copper.
As copper(II) oxide is formed, oxygen is removed
from the air
and the volume of air in the syringes is seen to
decrease.
• When the reaction is complete,
only 80% of the original volume of air remains.
This shows that the proportion of oxygen in the
air is about 20%.
Experiment using iron
• If the original volume was 15cm3 and the final
volume is 12cm3
• then the oxygen used up measured is 3 cm3.
% of oxygen
• = 3/15 *100
• = 20%
Experiment with phosphorous
2.18 describe the laboratory preparation of oxygen
from hydrogen peroxide
EQUATION:
Catalyst
Hydrogen peroxide
2H2O2
•
•
DESCRIPTION:
•
•
PROPERTIES:
•
•
TEST:
=
Water +
=
2H2O
Oxygen
+
O2
The apparatus is set up as shown above.
10 volume hydrogen peroxide is added slowly to the flask.
[CARE: If O2 is released too quickly the cork will explode out.]
Oxygen is collected by downward displacement of water.
Colourless, odourless gas.
Slightly soluble in water (hence fish can breathe in it).
Many substances, both elements and compounds,
burn in oxygen (and in air which is one fifth oxygen).
Oxygen relights a glowing splint.
2.19 describe the reactions with oxygen in air of magnesium, carbon and
sulphur, and the acid base character of the oxides produced
• Reaction with magnesium.
• What precaution you need to take? Why?
• Write a balanced chemical reaction for the
same .
Reaction with carbon and sulphur
Reaction of these oxides with water
• MgO
• CO2
• SO2
•
Which are acidic and which are basic
2.20 describe the laboratory preparation of carbon dioxide from calcium
carbonate and dilute hydrochloric acid
•
Adding dilute hydrochloric acid to calcium carbonate powder or chips.
The carbon dioxide gas is collected by downward delivery.
2.21 describe the formation of carbon dioxide from the thermal
decomposition of metal carbonates such as copper(II) carbonate
Observations
• What is the change in colour of the solid?
• What do you think are the new products?
• Write a balanced chemical reaction for the
reaction that has taken place.
2.22 recall the properties of carbon dioxide, limited to its solubility and
density