Air Chapter 31 Page 186

The Earth’s early atmosphere Early atmosphere formed by gases given out by volcanoes Mostly carbon dioxide with little or NO oxygen Most of the water vapour condensed and formed oceans Scientists believe that the Earth was formed about 4.5 billion years ago. Its early atmosphere was probably formed by the gases given out by volcanoes  it is believe that there was intense volcanic activity for the first billion years of the Earth’s existence. The early atmosphere was probably mostly carbon dioxide , with little or no oxygen. There were smaller proportions of water vapour, ammonia and methane. As the Earth cooled down, most of the water vapour condensed and formed oceans. It is thought that the atmospheres of Mars and Venus today which contain mostly carbon dioxide, are similar to the early atmosphere of the Earth. Smaller proportions of water vapour, ammonia and methane Very similar to the atmospheres of Mars and Venus

Changes to the early atmosphere So how did the proportion of carbon dioxide go down and the proportion of oxygen go up? The proportion of oxygen went up because of photosynthesis by plants. The proportion of carbon dioxide went down because: It was locked up in sedimentary rocks, such as limestone, and in fossil fuels. It was absorbed by plants for photosynthesis It dissolved in the oceans.

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? Most of the UK’s electricity is produced by power stations that are fuelled by fossil fuels, which contain carbon. Carbon dioxide is produced from burning fossil fuels, which is being added to the atmosphere faster than it can be removed. This means that the level of carbon dioxide in the atmosphere is increasing. Burning fossil fuels!

How can we prove air is a mixture? Its composition varies – in compounds the composition is constant 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? 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 MnO2 Hydrogen Peroxide Water + Oxygen MnO2 Manganese Dioxide

Oxygen Properties: Oxygen is a colourless, odourless, tasteless gas Oxygen is slightly heavier than air Oxygen is slightly soluble in water Oxygen is a neutral gas, it is not acidic or basic 5. Oxygen relights a glowing splint – this is the test for oxygen 6. Oxygen is a very reactive element. It combines with other elements to form oxides

Oxygen Acidic – Carbon dioxide C + O2  CO2 Basic – Magnesium Oxide 2Mg + O2 2MgO

Oxygen Uses: Breathing – our cells need oxygen to release energy from our food Welding – Cutting and welding requires a very hot flame, this is achieved when acetylene is mixed with oxygen 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 : MnO2 Remember: Reactants  Products Oxygen Chemical equation: 2H2O2 2H2O + O2 Word Equation : Hydrogen Peroxide Water + Oxygen MnO2 Manganese Dioxide

Testing for Oxygen Relight a glowing splint 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 CO2 is a colourless, odourless, tasteless gas It is an acidic gas – Turns blue litmus paper red Does not support combustion (burning) 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 Photosynthesis – green plants use it to make their food Fire Extinguishers – puts out fires 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.