Air

Chapter 31 Page 186

The Earth’s early atmosphere

Mostly carbon dioxide with little or NO oxygen

Early atmosphere formed by gases given

out by volcanoes

Smaller proportions of water vapour, ammonia

and methane

Most of the water vapour condensed and formed oceans

Very similar to the atmospheres of Mars and Venus

Changes to the early atmosphere

What is air made of?

Air is a mixture of different gasses

• Nitrogen N2

• Oxygen O2

• Noble Gasses Ar• Carbon Dioxide CO2

• Water Vapour H2O

Changes to today’s atmosphere

Where has this increase in carbon dioxide come

from?

Burning fossil fuels!

How can we prove air is a mixture?

1. Its composition varies – in compounds the composition is constant

2. If air is cooled down to low temperatures the gasses all become liquids at different temperatures – in compounds gasses would change state at the same time

The components of air can be separated individually

How can we prove air is a mixture?

3. When the gasses air mixed together in the right amounts they form air, no heat is given out or taken in so no new compound is made

How can we show the amount of oxygen in air?

The candle uses up all of the oxygen in the air until it goes out. The level that the water rises could be used to calculate approx. that 21% of air is made up of oxygen.

How can we show that the air contains carbon dioxide?

Carbon Dioxide, turns lime water milky.

How can we show that the air contains water vapour?

Turns blue cobalt chloride paper pink

Oxygen

Oxygen is prepared in the lab by looking at the breakdown of Hydrogen Peroxide

This is however a very slow reaction so we use a substance called a catalyst

A Catalyst is a substance that speeds up a chemical reaction without being used up in the reaction

Oxygen

Chemical equation: 2H2O2 2H2O + O2

Hydrogen Peroxide Water + Oxygen

MnO2

Manganese Dioxide

OxygenProperties:1. Oxygen is a colourless, odourless, tasteless gas2. Oxygen is slightly heavier than air3. Oxygen is slightly soluble in water4. Oxygen is a neutral gas, it is not acidic or basic 5. Oxygen relights a glowing splint – this is the test for oxygen6. Oxygen is a very reactive element. It combines with other elements to form oxides

Oxygen

Acidic – Carbon dioxideC + O2 CO2

Basic – Magnesium Oxide2Mg + O2 2MgO

OxygenUses:1. Breathing – our cells need oxygen to release

energy from our food2. Welding – Cutting and welding requires a

very hot flame, this is achieved when acetylene is mixed with oxygen

3. Burning – Oxygen is needed for the burning of fossil fuels

Preparing oxygen

We will look at this next week

03/12/13

Preparing Oxygen

Today we will

• Prepare oxygen using hydrogen peroxide and manganese dioxide

• Conduct the tests for oxygen

Preperation of Oxygen

Oxygen

Chemical equation: 2H2O2 2H2O + O2

Word Equation :

Hydrogen Peroxide Water + Oxygen

MnO2

Manganese Dioxide

Remember:Reactants Products

Testing for Oxygen

1. Relight a glowing splint

2. Neutral – moist red and blue litmus stay red and blue

10/12/13

Today we will…

Look at the production of Carbon dioxide

• How it is produced• Its properties• Its Uses

• We will make some!

Carbon Dioxide

Carbon Dioxide can be prepared in the lab by reacting dilute, Hydrochloric acid and marble chips

Calcium carbonate + Hydrochloric acid Calcium Chloride + Water + Carbon Dioxide

CaCO3 + 2HCl CaCl2 + H2O + CO2

Properties of Carbon Dioxide

1. CO2 is a colourless, odourless, tasteless gas2. It is an acidic gas – Turns blue litmus paper

red3. Does not support combustion (burning)4. It is denser than air

Properties of Carbon Dioxide

5. It turns limewater milky – this is the test for carbon dioxide

Ca(OH)2 + CO2 CaCO3 + H2O

Limewater + Carbon dioxide Chalk + Water

Properties of Carbon Dioxide

6. It dissolves in water to form an acidic solution that turns blue litmus paper red

CO2 + H2O H2CO3

Carbon dioxide + Water Carbonic Acid

Uses of Carbon Dioxide

1. Photosynthesis – green plants use it to make their food

2. Fire Extinguishers – puts out fires

3. Fizzy Drinks – It is dissolved under high pressure in fizzy drinks

The Production of CO2 (Pg 105)

• Procedure• Set up as shown (calcium carbonate is the chemical name for marble chips).

• Slowly release the hydrochloric acid into the flask underneath.

• Carbon dioxide is collected it the gas jar

• Test 1:Pour a small volume of limewater into the jar and shake – the limewater will turn milky showing that the gas is carbon dioxide.• Test 2:Add water to a fresh jar of carbon dioxide and test with blue litmus paper: it turns red demonstrating that it is an acid.