Air & Oxygen

RAG Sheet & WordBank

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What is the difference between the two methods you could use to

find the % oxygen in air?

The Atmosphere• Mixture of gases which forms a blanket

around the earth

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

Issues with experiment

• Night light goes out without all oxygen being used up

• Graduated cylinder does not measure volume as accurately as gas syringe

Composition of Air• To measure % oxygen in air using gas

syringe (MP)

• Main steps

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

Why it’s more accurate• More oxygen removed from air• Gas syringe is more accurate at

measuring volume

• Practical worksheet

What is the difference between the two methods you could use to

find the % oxygen in air?

• What is the significance of:cobalt chloride

limewaterlitmus

glowing splinta lighting splint going out?

Composition of AirGas Percentage in dry air

Nitrogen 78Oxygen 21

Inert gases & carbon dioxide

1

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

• Practical worksheet

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

Preparation of Oxygen (MP)

• Main steps– H2O2 dropped on to catalyst– Oxygen produced is collected over water as it

is only slightly soluble

Properties of oxygen (MP)• Oxygen is neutral• No change in colour of

red litmus or blue litmus paper

• Oxygen relights a glowing split

• Practical worksheet

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

• Practical worksheet

Properties of Oxygen (MP)• Burning magnesium in oxygen– Burns much brighter in oxygen then in air–Magnesium + oxygen magnesium oxide

Properties of Oxygen (MP)• Magnesium oxide and waterWord equation:Magnesium oxide + water

magnesium hydroxide– Red litmus turns blue a base is formed

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

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)

• What is the significance of:cobalt chloride

limewaterlitmus

glowing splinta lighting splint going out?

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

RAG Sheet & WordBank

Red Amber Green(No idea) (Some clue)

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• Worksheet• Exam questions• Mindmap