2.9: Know the Approximate Percentages by Volume of the Four Most Abundant Gases in Dry Air

THE COMPOSITION OF AIR:

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Table below shows the approximate percentage by volume of the main gases in unpolluted, dry Air:

GAS	PERCENTAGE IN AIR
NITROGEN	78 %
OXYGEN	21 %
ARGON	0.9 %
CARBON DIOXIDE	0.04 %

2.10: Understand How to Determine the Percentage by Volume of Oxygen in Air using Experiments Involving the Reactions of Metals (E.g Iron) and Non - Metals (E.g Phosphorus) with Air

DETERMINING PERCENTAGE VOLUME OF OXYGEN IN AIR USING METALS:

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PERCENTAGE VOLUME OF OXYGEN IN AIR - USING METALS

Diagram showing the Use of Iron to Calculate Percentage Volume of Oxygen in Air

METHOD: Place wet Iron fillings at the end of a burette (use Vaseline if Iron Filings does not stick) Use a clamp to hold the burette vertically in the trough of Water Measure and note the starting height of Water level in the burette Leave apparatus for several days Measure and note the final height of Water level in the burette

RESULTS: As the Water level will rise to replace the volume of Oxygen lost during reaction to form Iron (II) Oxide, a constant Water level will be reached as Iron fillings will fully oxidise with Oxygen in the air

CALCULATIONS: Volume of Air at the Start = ( Total Burette Volume - Initial Burette Reading) Volume of Oxygen Used (Reacted with Iron) = ( Initial Reading - Final Reading ) Percentage Volume of Oxygen Calculation:

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DETERMINING PERCENTAGE VOLUME OF OXYGEN IN AIR USING NON - METALS:

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PERCENTAGE VOLUME OF OXYGEN IN AIR - USING NON - METALS

Diagram showing the Use of Phosphorus to Calculate Percentage Volume of Oxygen in Air

METHOD: Add Phosphorus into an evaporating dish and place it on a trough of Water Ignite Phosphorus using a candle Cover evaporating dish with a bell jar Measure and note the starting height of the Water level in the bell jar Leave apparatus for several days Measure and note the final height of the Water level in the bell jar

RESULTS: As the Water level will rise to replace the volume of Oxygen lost during this reaction, a constant level will be reached as Phosphorus will use up all Oxygen in Air to burn (Oxygen is one of three Elements that a fire needs)

2.11: Describe the Combustion of Elements in Oxygen, Including Magnesium, Hydrogen and Sulfur

COMBUSTION: Chemical reaction involving burning (ignition)

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COMBUSTION OF ELEMENTS IN OXYGEN:

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ELEMENT	OBSERVATION DURING COMBUSTION	EQUATION FOR REACTION
MAGNESIUM	Intense white light (white flame) White powder produced	2Mg + O2 → 2MgO
HYDROGEN	Exothermic Water is produced	2H2 + O2 → 2H2O
SULFUR	Blue flame Colourless gas produced	S + O2  →  SO2

2.12: Describe the Formation of Carbon Dioxide from the Thermal Decomposition of Metal Carbonates, Including Copper (II) Carbonate

THERMAL DECOMPOSITION: Breakdown of Compounds using heat energy

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THERMAL DECOMPOSITION OF METAL CARBONATES:

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Carbon Dioxide is produced when Metal Carbonates are heated through Thermal Decomposition:

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Metal Carbonate      →      Metal  Oxide     +      Carbon Dioxide

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Example: Copper (II) Carbonate

                   Diagram showing the Thermal Decomposition of Copper (II) Carbonate

When Copper (II) Carbonate is Thermally Decomposed, it Turns from Green (Copper (II) Carbonate) to Black (Copper Oxide)

2.13: Know that Carbon Dioxide is a Greenhouse Gas and that Increasing Amounts in the Atmosphere May Contribute to Climate Change

CARBON DIOXIDE: Greenhouse gas that contributes to climate change when present in large amounts

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ENHANCED GREENHOUSE EFFECT: Caused by the increased concentration and effect of Greenhouse Gases

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CARBON DIOXIDE AND CLIMATE CHANGE:

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THE ENHANCED GREENHOUSE EFFECT - CLIMATE CHANGE

Diagram Showing How the Enhanced Greenhouse Effect Occurs

EXPLANATION: Sun emits short wave radiation (ultraviolet radiation) that enters the Earth's atmosphere Earth's surface absorbs short wave radiation from the sun and re-emits it as long wave radiation (infrared/heat) Greenhouse gases - such as Carbon Dioxide, absorb and re-radiate this long wave radiation, retaining heat within the atmosphere Earth’s average temperature rises as a result

CONSEQUENCES: Climate change due to increase in Earth’s atmospheric temperature Spread of disease due to cold climate Migration of species as they will move to areas that are more habitable (No droughts) Extreme weather conditions due to climate change Extinction of species due to inhabitable environment Acidification of oceans due to increasing Carbon Dioxide levels Rise in water levels due to melting ice caps Destruction of habitat due to climate change (for animals that live on glaciers)

2.14: Practical: Determine the Approximate Percentage by Volume of Oxygen in Air Using Metal or Non-Metal

DETERMINING PERCENTAGE VOLUME OF OXYGEN IN AIR USING METALS:

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PERCENTAGE VOLUME OF OXYGEN IN AIR - USING METALS

Diagram showing the Use of Iron to Calculate Percentage Volume of Oxygen in Air

METHOD: Place wet Iron fillings at the end of a burette (use Vaseline if Iron Filings does not stick) Use a clamp to hold the burette vertically in the trough of Water Measure and note the starting height of Water level in the burette Leave apparatus for several days Measure and note the final height of Water level in the burette

RESULTS: As the Water level will rise to replace the volume of Oxygen lost during reaction to form Iron (II) Oxide, a constant Water level will be reached as Iron fillings will fully oxidise with Oxygen in the air

CALCULATIONS: Volume of Air at the Start = ( Total Burette Volume - Initial Burette Reading) Volume of Oxygen Used (Reacted with Iron) = ( Initial Reading - Final Reading ) Percentage Volume of Oxygen Calculation:

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DETERMINING PERCENTAGE VOLUME OF OXYGEN IN AIR USING NON - METALS:

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PERCENTAGE VOLUME OF OXYGEN IN AIR - USING NON - METALS

Diagram showing the Use of Phosphorus to Calculate Percentage Volume of Oxygen in Air

METHOD: Add Phosphorus into an evaporating dish and place it on a trough of Water Ignite Phosphorus using a candle Cover evaporating dish with a bell jar Measure and note the starting height of the Water level in the bell jar Leave apparatus for several days Measure and note the final height of the Water level in the bell jar

RESULTS: As the Water level will rise to replace the volume of Oxygen lost during this reaction, a constant level will be reached as Phosphorus will use up all Oxygen in Air to burn (Oxygen is one of three Elements that a fire needs)