Gases in the Atmosphere

Question 1

(dry) air is a mixture of which gases?

Answer 1

78% nitrogen
21% oxygen
1% argon
0.04% carbon dioxide

Question 2

proportion of oxygen in the atmosphere (iron)

Answer 2

1. soak iron wool in acetic acid. then push the wool into a measuring cylinder and invert the measuring cylinder into a beaker of water
2. record starting position of water = starting volume of air
3. over time level of water will rise. this is because the iron reacts with the oxygen in the air to make iron oxide. the water rises to fill the space the oxygen took up
4. leave for around a week
5. record the finishing position of the water = final air volume

Question 3

proportion of oxygen in the atmosphere (phosphorus)

Answer 3

1. place phosphorus in a tube and attach a glass syringe at either end. make sure one of the syringes is filled with air and other is empty
2. heat phosphorus and use syringes to pass air over it. phosphorus will react with oxygen to make phosphorus oxide
3. as it reacts the amount of air in the syringes will decrease
4. measure starting and final volumes of air using the scale on one of the syringes
5. then calculate % of oxygen

Question 4

% of oxygen equation

Answer 4

start volume - final volume / start volume x 100

Question 5

combustion of magnesium in oxygen

Answer 5

• bright white flame
• forms magnesium oxide = white powder
• slightly alkaline in water

Question 6

combustion of hydrogen in oxygen

Answer 6

• burns very easily in oxygen with an orange yellow flame

- produces water vapour

Question 7

combustion of sulphur in oxygen

Answer 7

• pale blue flame
• produces sulphur dioxide
• acidic in water

Question 8

thermal decomposition of metals produces CO2

Answer 8

metal carbonate = carbon dioxide + metal oxide

• heat eg. copper (II) carbonate then collect gas given off in a test tube. gas can then be tested to see if it’s CO2

Question 9

test for chlorine

Answer 9

bleaches damp blue litmus paper, turning it white

Question 10

test for oxygen

Answer 10

relights a glowing splint

Question 11

test for carbon dioxide

Answer 11

turns limewater cloudy

Question 12

test for hydrogen

Answer 12

makes a ‘squeaky pop’ with a lighted splint

Question 13

test for ammonia

Answer 13

turns damp red litmus paper blue (very strong smell)

Question 14

chemical test for water

Answer 14

add water to anhydrous copper (II) sulphate and see if the white powder turns blue. this will tell you if water is PRESENT but not if it is pure water

Question 15

how to tell if water is pure

Answer 15

will always boil at 100C and freeze at 0C