Oxygen And Oxides, hydrogen and water

Question 1

Gases in the air

Answer 1

Nitrogen- 78%
Oxygen - 21%
CO2 - 0.04%
Argon - <1%

Question 2

Using copper to investigate the proportion of oxygen in the atmosphere

Answer 2

• heat an excess of copper in a tube and pass air over it using two syringes
• Mark the syringe to tell how much oxygen has been used up
• The copper goes to copper (II) oxide
• if you start with 100 cm³, you should end up with about 80 cm³

Question 3

Using iron or phosphorus to investigate the proportion of oxygen in the atmosphere

Answer 3

• Iron reacts with oxygen in air to form rust, white phosphorus smoulders in air to produce phosphorus oxide
• first soak some iron wool in acetic acid and put this in a test tube inverted in a beaker of water
• over time, the level of water in the test tube will rise because the iron reacts with oxygen to make iron oxide and the water rises to fill the space
• to work out percentage mark starting and finishing positions of the water

Question 4

Making oxygen in the lab

Answer 4

• hydrogen peroxide Will decompose to water and oxygen
• manganese (IV) oxide catalyst
• collect the oxygen either in a test tube or gas syringe

Question 5

Burning elements (magnesium, carbon, sulphur) in air

Answer 5

magnesium:
- bright white flame, white powder is formed (magnesium oxide), slightly alkaline

Carbon:
- Orange/yellow flame, produces carbon dioxide gas, slightly acidic

Sulphur:
- pale blue flame, produces sulphur dioxide, acidic

Question 6

Calcium carbonate to produce carbon dioxide

Answer 6

• calcium carbonate (marble chips) is put in the bottom of the flask containing HCL
• hydrochloric acid + calcium carbonate -> calcium chloride + water + carbon dioxide

Question 7

Thermal decomposition of metal carbonates also produces carbon dioxide

Answer 7

Copper (II) carbonate is it green powder that will easily decompose to form carbon dioxide and copper (II) oxide when you heat it

Question 8

Properties of carbon dioxide

Answer 8

• CO2 is slightly soluble in water and dissolves into drinks when under pressure
• CO2 it’s more dense than air so it sinks onto the flames and stops oxygen getting to it
• CO2 is an insulating layer in the atmosphere

Question 9

Reactions of metals with dilute acid (release hydrogen)

Answer 9

Magnesium- magnesium reacts vigourously and produces loads of bubbles

Aluminium- aluminium doesn’t react much with cold acid because it has a protective aluminium oxide layer, but in warm, it reacts vigourously and produces a lot of bubbles

Zinc/Iron- react slowly with acid but more strongly if you heat them up

Question 10

Combustion of hydrogen

Answer 10

Hydrogen burns in oxygen to form water.

hydrogen + oxygen → water

2H2 + O2 → 2H2O

The flame is almost colourless.

Question 11

What do use for the chemical test of water

Answer 11

Anhydrous copper (II) sulfate

Question 12

Physical test to show whether water is pure

Answer 12

• boils 100° C

- Freezes 0° C