Gases In The Atmosphere

Question 1

Percentage of nitrogen in the air

Answer 1

78%

Question 2

Percentage of oxygen in the air

Answer 2

21%

Question 3

Percentage of water in the air

Answer 3

0.04%

Question 4

Percentage of carbon dioxide in the air

Answer 4

0.04%

Question 5

Percentage of argon in the air

Answer 5

0.9%

Question 6

How do you determine the percentage of O2 in the air using a metal?

Answer 6

The percentage of oxygen in the air can be measured by passing a known volume of air over hot copper and measuring the decrease in volume as the oxygen reacts with it using gas syringes.

Question 7

How do you determine the percentage of O2 in air using phosphorous?

Answer 7

The phosphorus is lit with a hot wire. It reacts with oxygen in the air and causes the water level in the jar to rise by about 20%.

Question 8

What can you use instead of phosphorus and why would this be ideal?

Answer 8

Phosphorus is quite toxic, so you may also use iron.

Question 9

Observations of combustion of magnesium in oxygen.

Answer 9

Bright white flame.

Question 10

Magnesium + oxygen ->

Answer 10

Magnesium oxide

Question 11

Product of combustion of magnesium in oxygen and its pH

Answer 11

MgO is a base (8-10 pH)

Question 12

Sulphur + oxygen ->

Answer 12

Sulphur dioxide

Question 13

State and colour of magnesium at room temperature

Answer 13

Shiny grey solid

Question 14

State and colour of magnesium oxide at room temperature

Answer 14

White powder

Question 15

State and colour of sulphur at room temperature

Answer 15

Yellow powder

Question 16

State and colour of sulphur dioxide at room temperature

Answer 16

White fumes (gas)

Question 17

Observations of combustion of sulphur in oxygen.

Answer 17

Blue flame

Question 18

pH of sulphur dioxide

Answer 18

A strong acid

Question 19

Combustion of hydrogen in oxygen observations

Answer 19

Colourless flame

Question 20

Hydrogen state and colour at room temperature

Answer 20

Colourless gas

Question 21

Test for hydrogen

Answer 21

Hold a burning splint near test tube - if it pops, hydrogen is present.

Question 22

Observations from the thermal decomposition of copper carbonate

Answer 22

Green powder (copper carbonate) turns into a black powder (copper oxide)

Question 23

Copper (II) carbonate ->

Answer 23

Copper oxide + carbon dioxide

Question 24

On heating, —— decompose into —— and CO2.

Answer 24

1. Metal carbonates

2. Metal oxides

Question 25

Why is CO2 harmful for the environment?

Answer 25

• CO2 is a greenhouse gas
• it absorbs infra red radiation and therefore warms up the atmosphere
• this leads to global warming, which may cause climate change.