Air

Question 1

Describe the composition of air

Answer 1

The air is made up of:
78% nitrogen
21% oxygen
1% argon, carbon dioxide and water vapour

Question 2

Describe an experiment to show that oxygen makes up almost 1/5 of air.

Answer 2

Steel wool is packed into a graduated cylinder inserted over water.
Leave for about one week.
Measure the height that the water has risen up the cylinder.

Result
Water rises in the graduated cylinder 1/5 of the way up to replace the oxygen that is lost.
The oxygen in the air has reacted with the steel to form rust.

Conclusion
1/5 of air is made up of oxygen

Question 3

Describe and experiment to show that there is carbon dioxide present in air

Answer 3

Set up the apparatus as shown in the diagram. Air is pumped through the clear limewater.
Result
The limewater will turn milky as carbon dioxide is present.
Limewater turns milky in the presence of carbon dioxide.

Conclusion
Carbon dioxide is present in air.

Question 4

Describe an experiment to show there is water vapour in air

Answer 4

Set up the apparatus as shown in the diagram.
Dry the outside of the test tube fully.
After a short time small droplets of clear liquid condense on the outside of the test tube.
Place a tub of

Result:
Cobalt chloride paper will turn red

Conclusion
Air contains water vapour

Question 5

List the properties of oxygen

Answer 5

It is a colourless, oderless gass.
Oxygen gas will relight a glowing splint.
Oxygen gas supports combustion.
It is a neutral gas.

Question 6

Describe an experiment to prepare a sample of oxygen

Answer 6

Tap of the funnel is opened and a few drops of hydrogen peroxide falls onto the manganese dioxide.

Result
Oxygen collects in the gas jar

Conclusion
Oxygen is prepared by the breakdown of hydrogen peroxide into hydrogen and oxygen. Manganese dioxide is the catalyst in this reaction.

Question 7

What is the chemical formula for the experiment (preparing a sample of oxygen)

Answer 7

Hydrogen peroxide ———————– water and oxygen
Manganese dioxide

H2O2———- H2O + O2
MNO2

Question 8

What is a catalyst

Answer 8

A chemical that speeds up or slows down a chemical reaction without itself being changed or used up.

Question 9

Describe two ways to test for oxygen

Answer 9

Oxygen delights a glowing splint
(Oxygen supports combustion)

Oxygen has no effect on moist red or blue litmus paper
(No colour change- oxygen is neutral/ph7)

Question 10

Name three uses for oxygen

Answer 10

Breathing
Welding
Burning

Question 11

List the properties of carbon dioxide

Answer 11

It is a colourless odorless gas.
It does not support combustion (it will extinguish a flame)
It is more dense than air.
It turns limewater milky.

Question 12

Describe an experiment to prepare a sample of carbon dioxide

Answer 12

Set up apparatus as shown in diagram.
Slowly allow dilute hydrochloric acid to fall onto marble chips.
Continue to add the acid as necessary to maintain the reaction.
Collect three gas jars of the carbon dioxide and perform the tests to test for carbon dioxide.

Result
The chips fizz as they react with the acid, creating carbon dioxide.

Conclusion
Carbon dioxide is prepared by the reaction between dilute hydrochloric acid (hol) and marble chips( calcium carbonate)

Question 13

Describe three ways to test for carbon dioxide

Answer 13

Test its ph by adding moist red and blue litmus paper
(Moist blue litmus turns red, showing it is acidic)

Pour limewater into a jar of carbon dioxide gas
(The limewater will turn milky, confirming the presence of carbon dioxide)

Place a lit candle in an empty beaker. Invert a gas jar above the beaker and wait.
(The candle is extinguished, showing us that it is more dense than air and does not support combustion)

Question 14

What does magnesium burn brightly with?

Answer 14

Oxygen

Question 15

Describe three tests to test the properties of carbon dioxide

Answer 15

Test its ph by adding pieces of moist red and blue litmus paper.
It causes the blue litmus paper to turn red showing it is an acidic gas.

Pour a small volume of limewater into a jar of carbon dioxide gas and shake for ten seconds.
The limewater colour changes from clear to milky.

Place a lot candle in an empty beaker and invert a gas jar of carbon dioxide over it.
The candle is extinguished by the carbon dioxide showing:
It is more dense than air and does not support combustion

Question 16

Describe a test for carbon dioxide

Answer 16

When carbon dioxide comes into contact with limewater(calcium hydroxide) they react together and from calcium carbonate and water.

Ca(OH)2 + Co2 — CaCo3 + H20

The calcium carbonate produced is insoluble in water and causes the solution to change colour from clear to milky.

(Carbon dioxide turns limewater milky)

Question 17

Describe three uses of carbon dioxide

Answer 17

Refrigeration, stage effects and fizzy drinks.