1gases in the atmosphere

Question 1

the earths atmosphere is made up of

Answer 1

78% nitrogen, 21% oxygen, 0.9% argon, 0.04% CO2

Question 2

the percentage of oxygen in air can be found by

Answer 2

reacting a metal or non metal with the oxygen in a fixed volume of air- one way to carry this out is to burn a small amount of phosphorus in a bell jar that is sitting in a trough of water

Question 3

percentage of oxygen using phosphorus and a bell jar

Answer 3

initially, the water levels are the same inside and outside the jar. As the phosphorus burns it uses up the oxygen inside the bell jar and the water level rises
By making careful measurements of water levels before and after the experiment you can determine the percentage of oxygen in the air
Phosphorus is very suitable for this experiment as it burns readily until all the available oxygen is used up
A disadvantage of this experiment is that phosphorus is toxic, so it is hazardous and great care must be taken to handle it safely

Question 4

method to determine the % of oxygen in the air

Answer 4

Firstly, you will need to measure the volume between the final mark on the scale and the tap (stopcock)
Fill the burette with water up to lowest mark, 50.0 mL, and then let it drain into a small measuring cylinder
Measure the volume of water
Add a little water to moisten the inside of the burette
Make sure the tap is closed and sprinkle some iron filings or push a piece of iron wool into the bottom of the burette
Invert the burette into a trough of water and clamp the burette vertically
Note and record the position of the water level
After 3-4 days note the new position of the water level

Question 5

combustion is

Answer 5

burning

Question 6

all combustion reactions involve a

Answer 6

chemical change in which oxygen reacts with elements or compounds to produce oxides

Question 7

combustion gives out heat so is a

Answer 7

exothermic reaction

Question 8

observation of magnesium in combustion

Answer 8

Intense white flame
White powder produced (magnesium oxide)
2Mg (s) + 02(g) -> 2MgO (s)

Question 9

observation of hydrogen in combustion

Answer 9

Exothermic
Water is produced
2H2(g) + 02 (g) -> 2H2O (I)

Question 10

observation of sulfur in combustion

Answer 10

Blue flame
Colourless, poisonous gas produced
S(s) + O2(g) -> SO2 (g)

Question 11

thermal decomposition is the

Answer 11

term used to describe reactions where a substance breaks down due to the action of heat

Question 12

one reaction of thermal decomposition is

Answer 12

metal carbonates

Question 13

metal carbonate ->

Answer 13

metal carbonate → metal oxide + carbon dioxide

Question 14

thermal decomposition of copper (II) carbonate

Answer 14

The thermal decomposition of copper(II)carbonate occurs readily on heating
Copper(II) carbonate is a green powder and slowly darkens as black copper(II) oxide is produced
The carbon dioxide given off can be tested by passing the gas through limewater and looking for it to turn milky

Question 15

equation for the decomposition of copper (II) carbonate

Answer 15

CuCO3 (s) → CuO (s)+ CO2 (g)

copper(II) carbonate → copper(II) oxide + carbon dioxide

Question 16

when shortwave radiation from the sun

Answer 16

strikes the Earth’s surface it is absorbed and re-emitted from the surface of the Earth as infrared radiation

Question 17

much of radiation is trapped

Answer 17

inside the Earth’s atmosphere by greenhouse gases which can absorb and store the energy- carbon dioxide, methane and water vapour are gases which have this affect

Question 18

increasing levels of carbon dioxide

Answer 18

although present in only a small amount, is causing significant upset to the Earth’s natural conditions by trapping extra heat energy
This process is called the enhanced greenhouse effect

Question 19

sources of carbon dioxide

Answer 19

Combustion of wood and fossil fuels, respiration of plants and animals, thermal decomposition of carbonate rocks and the effect of acids on carbonates