Air & Oxygen
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Transcript of Air & Oxygen
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Air & Oxygen
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RAG Sheet & WordBank
Red Amber Green(No idea) (Some clue)
(Know it)
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What is the difference between the two methods you could use to
find the % oxygen in air?
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The Atmosphere• Mixture of gases which forms a blanket
around the earth
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Composition of Air • Investigate the % of oxygen in the air,
using a night light (MP)
• Main steps– Floating night light, lit, graduated cylinder
over it–Water rises– Allow to cool, measure volume of gas left– Not very accurate, air is oxygen
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Issues with experiment
• Night light goes out without all oxygen being used up
• Graduated cylinder does not measure volume as accurately as gas syringe
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Composition of Air• To measure % oxygen in air using gas
syringe (MP)
• Main steps
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Composition of air
• Reaction: Copper + Oxygen Copper oxide– Start with 100cm3 of air (100%)– Volume at end of reaction 79cm3 (79%)– Volume of oxygen reacted with copper =
21cm3 21% oxygen
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Why it’s more accurate• More oxygen removed from air• Gas syringe is more accurate at
measuring volume
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• Practical worksheet
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What is the difference between the two methods you could use to
find the % oxygen in air?
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• What is the significance of:cobalt chloride
limewaterlitmus
glowing splinta lighting splint going out?
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Composition of AirGas Percentage in dry air
Nitrogen 78Oxygen 21
Inert gases & carbon dioxide
1
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Composition of Air• To show that carbon dioxide & water
vapour are present in air (MP)
– Cobalt chloride paper goes from blue to pink in presence of water
– Limewater goes milky/cloudy in presence of CO2
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• Practical worksheet
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Preparation of oxygenDecomposition of hydrogen peroxide
Word equationHydrogen peroxide water + oxygen
Chemical equation (HL)2H2O2 2H2O + O2
–This reaction requires a catalyst–Substance which speeds us a chemical reaction but is not used up in the reaction itself–Catalyst in this reaction is manganese dioxide/MnO2
MnO2
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Preparation of Oxygen (MP)
• Main steps– H2O2 dropped on to catalyst– Oxygen produced is collected over water as it
is only slightly soluble
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Properties of oxygen (MP)• Oxygen is neutral• No change in colour of
red litmus or blue litmus paper
• Oxygen relights a glowing split
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• Practical worksheet
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Properties of oxygen (MP)• Burning carbon in
oxygen• Another name for
burning is combustion• Rxn: Carbon + oxygen
carbon dioxide• C + O2 CO2
• Limewater turns milky• Carbon dioxide +
water turns blue litmus paper red acidic gas
• Carbon dioxide quenches a burning split
• Denser then air
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• Practical worksheet
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Properties of Oxygen (MP)• Burning magnesium in oxygen– Burns much brighter in oxygen then in air–Magnesium + oxygen magnesium oxide
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Properties of Oxygen (MP)• Magnesium oxide and waterWord equation:Magnesium oxide + water
magnesium hydroxide– Red litmus turns blue a base is formed
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Properties of Oxygen - summary
Physical Properties Chemical PropertiesColourless, odourless, tasteless gas
Supports combustions, substance burn more vigorously
Slight soluble in water Reacts with most elements to form oxides
Slightly heavier then air No effect on litmus
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Summary of reactions with O2
Element Reaction with O2
Compound formed
Effect of compound on
moist litmus paper
Carbon Glows brightly
Carbon dioxide
Blue litmus turns red (acidic)
Magnesium Burns vigorously
Magnesium oxide
Red litmus turns blue (basic)
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• What is the significance of:cobalt chloride
limewaterlitmus
glowing splinta lighting splint going out?
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Uses of Oxygen• Breathing– Stored in cylinders– Used in hospitals and by mountain climbers
• Burning and welding– Acetylene in O2 reaches 3000C
– Flame can cut through melting or melt metal and join them together
• Space rockets – Need to bring own oxygen to space for
combustion
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RAG Sheet & WordBank
Red Amber Green(No idea) (Some clue)
(Know it)
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• Worksheet• Exam questions• Mindmap