The Atmosphere

The atmosphere is a layer of gases around the earth. These gases are

collectively known as air.

Oxygen21%

Argon, Carbon Dioxide, Water vapour

1%

Nitrogen78%

Gases in atmosphere

Percentages of gases in the air

• NITROGEN 78%• OXYGEN 21%• CARBON DIOXIDE 0.03%• WATER VARIES• Neon and argon 1%

To show that there is water vapour in the air

1. Set up as shown2. Leave for 30 mins3. Drops of water form on the outside of the tube4. Test water with blue cobalt chloride paper

Result ; the blue cobalt chloride paper turns pink proving that water is present in the air and that the water condensed on the cold test tube.

Another test for water:Water turns Anhydrous copper sulfate(white) to hydrated copper sulfate (blue)

To show that there is carbon dioxide in the air

1. Set up the apparatus as shown in the the diagram2. Use a vacuum pump to draw a current of air

through the lime water in the test tube

Result : after a few minutes the limewater turns milky

Conclusion : the air contains carbon dioxide

To show that approx one fifth of air is Oxygen

• Three different experiments

1. To show one fifth of air is oxygen1. Pack steel wool in bottom of a graduated cylinder2. Invert cylinder in basin of water3. Mark level of water on the cylinder4. Leave for one week5. Measure height that the water rises up the

cylinder

Result: • When iron rusts it uses up oxygen. When

there is sufficient iron and water present, rusting will continue until all of the oxygen is used up.

2. To show one fifth of air is oxygen

Method1.Fill a trough ¼ full with water2.Light a night light and float on water3.Unscrew cap of plastic bottle and place over night light4.Mark the level of the water5.Replace the cap on the bottle tightly6.Observers what happens7.Mark the new level of water in the plastic bottle

ResultThe water rises inside the bottle because the oxygen in the air is used up in combustionCombustion is a chemical reaction in which a fuel reactive with oxygen to give out heat

3. To show one fifth of air is oxygen

• Set up apparatus• Before heating, ensure one syringe contains 100cm3

of air and other is closed• Heat copper turnings and slowly pass the 100cm3

from one syringe to the other• Continue until the volume does not change• Cool down apparatus and record volume.

Gas syringe 1 Gas syringe 2

Bunsen burner

Copper powder Silica tube

• Result: • Volume will go down to approx 80cm3 and the

copper turnings turn a grey/black in colour. This is because the copper reacts with the oxygen present forming copper oxide. The oxygen is used up in this process to make the oxide and therefore the volume of oxygen in the air goes down.

Preparation of oxygen

• Oxygen is prepared by the chemical breakdown of hydrogen peroxide H2O2 using manganese dioxide MnO2 as a catalyst

• A catalyst is a substance that speeds up a chemical reactions but are not used up in the reaction.

Equation To prepare and examine oxygen gas

hydrogen peroxide oxygen + water

manganese dioxide

2H2O2 O2 + 2H20MnO2

To prepare and collect oxygen gas

1. Set up as shown2. Open the tap on the funnel and add the

hydrogen peroxide slowly to the black solid manganese dioxide

3. The oxygen gas is collected over water as oxygen is only slightly soluble in water

4. Three test tubes of the gas are collected for tests.

PREPARATION O2

Properties of Oxygen

1. Note colour and smell2. Test pH

3. Place a glowing splint into jar of O2

• 4. Heat carbon (charcoal) in combustion spoon over a bunsen and transfer to jar of oxygen, test products with litmus and limewater.

To burn carbon and magnesium in oxygen and test the products using moist litmus paper

• When an element is burned in air, a compound called an oxide is formed.

• Magnesium + Oxygen Magnesium oxide• Carbon + Oxygen Carbon dioxide• Care: Magnesium ribbon burns with an intense

white light that can be damaging to the retina.

Procedure: magnesium• Get a piece of magnesium ribbon• Using a tongs, hold the magnesium in the flame

of the Bunsen burner until it catches fire.• Put the burning magnesium in the test tube of

oxygen. Observe what happens.• Result: A white powder magnesium oxide is

formed. When water is added the magnesium oxide forms a base called magnesium hydroxide. Magnesium hydroxide is a base and it is used to neutralise stomach acid and it is found in Milk of Magnesia.

Combustion spoon

O2

Properties of oxygen

• Physical properties1. Colourless2. Odourless3. Tasteless4. Slightly heavier than air5. Slightly soluble in water

Chemical properties6. Supports combustion7. Neutral substance – neither acid or base, no effect on litmus

Uses of oxygen

• Burning • Welding• Breathing• Metals and non metals burn in oxygen to

produce oxides

Preparation of Carbon Dioxide

Hydrochloric acid + Calcium carbonate

= calcium chloride + carbon dioxide + water

CaCO3 + 2HCl → CaCl2 + CO2 + H2O

To prepare

CO2

• Set up as shown• Slowly add the HCl from the tap funnel• Observe the bubbles of CO2 gas produced when

the HCl hits the calcium carbonate.• The Carbon dioxide produced collects in the gas

jar.• Uses of carbon dioxide:1. In fizzy drinks2. In fire extinguishers

1. Note colour and smell2. pH3. Limewater test4. Test if supports combustion

Test for

CO2: it

turns limewater

milky

CO2 is heavier than air CO2 does not support combustion

Main Uses of Carbon Dioxide CO2

• Fizzy Drinks– All fizzy drinks contain CO2 under pressure

• Fire Extinguishers– CO2 is denser than air and does not support combustion

• Refrigeration– CO2 under pressure can be converted into a solid: Dry Ice. It is much

colder than ice –78oC

• Dry Ice- Special Effects on Stage– Lumps of dry Ice are put into warm water and wet CO2 carries clouds

of water vapour with it. Mist Effect