Topic 3: Gases in the atmosphere

Question 1

what percentage of air is made up of each of the four most abundant gas

Answer 1

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

Question 2

which practical involving the reactions of metals with air can be used to investigate the percentage of oxygen in air?

Answer 2

Iron:
-soak iron wool in acetic acid and push into a measuring cylinder.
-turn the measuring cylinder upside-down and place it in a beaker of water
-record the starting point of the water in the measuring cylinder and then as time goes on the oxygen reacts with the iron and the water level rises. leave it until it stops rising.
-record the final position of the water

start volume - final volume
————————————– x 100
start volume

Question 3

which practical involving the reactions of non-metals with air can be used to investigate the percentage of oxygen in air?

Answer 3

phosphorus:
-place the phosphorus in a tube with a gas syringe attached to each end. make sure one syringe is filled with air, and one is empty
-heat the phosphorus and use the syringes to push the air back and forth over it to make the oxygen react with the phosphorus
-measure the start and end volume in the filled syringe and calculate the percentage using the formula.

Question 4

describe the combustion of elements in oxygen (magnesium, hydrogen and sulphur and the acid-base character of the oxides produced)

Answer 4

Magnesium- burns with a bright white flame and produces magnesium oxide which is slightly alkaline when dissolved in water.
Hydrogen- burns very easily with oxygen, can be explosive, and burns with an orange/yellow flame. it produces water as water vapour.
Sulfur- burns with a pale blue flame and produces sulfur dioxide which is acidic when dissolved in water.

Question 5

describe the formation of carbon dioxide from the thermal decomposition of metal carbonates, including copper(II) carbonate.

Answer 5

if you heat a metal carbonate you get a metal oxide and carbon dioxide. this is an example of thermal decomposition, which is when substances break down into simpler substances when heated.
copper(II) carbonate is a green powder that will easily decompose to form carbon dioxide and copper(II) oxide when you heat it

Question 6

chemical test for oxygen

Answer 6

relights a glowing splint

Question 7

chemical test for hydrogen

Answer 7

when in contact with a lit splint it produces a squeaky pop sound.

Question 8

chemical test for carbon dioxide

Answer 8

when bubbled through limewater it turns the limewater cloudy

Question 9

chemical test for ammonia

Answer 9

ammonia turns damp reed litmus paper blue

Question 10

chemical test for chlorine

Answer 10

bleaches damp blue litmus paper.

Question 11

how do you carry out and interpret the results of the chemical test for water

Answer 11

if you add a few drops of your solution to anhydrous copper(II) sulfate it will turn blue if water is present.

Question 12

how to test if the substance is pure water

Answer 12

boils at 100 c
freezes at 0 c