air
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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. Smaller proportions of water vapour, ammonia and methane. - PowerPoint PPT PresentationTRANSCRIPT
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Air
Chapter 31 Page 186
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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
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Changes to the early atmosphere
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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
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Changes to today’s atmosphere
Where has this increase in carbon dioxide come
from?
Burning fossil fuels!
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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
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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
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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.
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How can we show that the air contains carbon dioxide?
Carbon Dioxide, turns lime water milky.
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How can we show that the air contains water vapour?
Turns blue cobalt chloride paper pink
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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
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Oxygen
Chemical equation: 2H2O2 2H2O + O2
Hydrogen Peroxide Water + Oxygen
MnO2
Manganese Dioxide
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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
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Oxygen
Acidic – Carbon dioxideC + O2 CO2
Basic – Magnesium Oxide2Mg + O2 2MgO
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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
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Preparing oxygen
We will look at this next week
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03/12/13
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Preparing Oxygen
Today we will
• Prepare oxygen using hydrogen peroxide and manganese dioxide
• Conduct the tests for oxygen
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Preperation of Oxygen
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Oxygen
Chemical equation: 2H2O2 2H2O + O2
Word Equation :
Hydrogen Peroxide Water + Oxygen
MnO2
Manganese Dioxide
Remember:Reactants Products
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Testing for Oxygen
1. Relight a glowing splint
2. Neutral – moist red and blue litmus stay red and blue
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10/12/13
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Today we will…
Look at the production of Carbon dioxide
• How it is produced• Its properties• Its Uses
• We will make some!
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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
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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
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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
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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
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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
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The Production of CO2 (Pg 105)
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• 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.