Pure Chemistry Chap 22 Maintaining Air Quality

Highly reccomended for YISS students

Characteristics of Carbon Monoxide

Colourless and odourless

Source of Carbon Monoxide

Incomplete combustion (i.e. insufficient oxygen available) of carbon-containing fuels.

Chemical equation for Carbon Monoxide formation

Using methane: 2CH4(g)+3O2(g)→2CO(g)+4H2O(g)

Using Propane: C3H8(l)+3.5O2(g)→3CO(g)+4H2O(l)

Effects of Carbon Monoxide

Toxic Binds irreversibly with haemogoblin in blood, forming carboxyhaemogoblin, reducing the oxygen carrying capacity of blood, leading to death Causes respiratory/breathing difficulties

Methods of removal/treatment for Carbon Monoxide

Use a catalytic converter in cars: Carbon monoxide and oxides of nitrogen are reduced to form carbon dioxide and nitrogen. (Increases CO2 produced) Use of alternative clean fuels like hydrogen/electric-powered vehicles

Characteristics of oxides of nitrogen

NO is colourless and odourless. NO2 is brown in colour and pungent.

Sources of oxides of nitrogen

High temperatures in vehicle combustion engines Heat released by lightning activity (N2+O2 —> 2NO) (2NO+O2->2NO2)

Effects of oxides of Nitrogen

Reacts with oxygen to form acidic compounds that dissolves in rainwater forming acid rain (4NO2+2H2O+O2->4HNO3)

• Corrodes steal/metal/marble/concrete structures and buildings.

• Harms and kills aquatic life and plants as it lowers pH/increases acidity of lakes

Reacts with unburnt hydrocarbon in the presence of sunlight to form photochemical smog/ozone

• Causes breathing difficulties, irritates eyes and lungs

Methods of removal/treatment of oxides of Nitrogen

Use a catalytic converter in cars: oxides of nitrogen and carbon monoxide are reduced to form carbon dioxide and nitrogen Use of alternative clean fuels like hydrogen/electric powered vehicles Use of calcium carbonate (powdered limestone) to reduce acidity and restore lakes and rivers polluted by acid rain.

Characteristics of sulfur dioxide

Colourless and pungent

Sources of sulfur dioxide

Volcanic eruptions Combustion of fossil fuels/sulfur -containing fuels Combustion of sulfur-containing coal in power stations

Effects of Sulfur dioxide

Reacts with oxygen to form acidic compounds that dissolves in rainwater forming acid rain. (SO2+H2O—>H2SO3 [slowly oxidised —> H2SO4])

• Corrodes steel/metal/marble/concrete structures and buildings.

• Harms and kills aquatic life and plants as it lowers pH/increases acidity of lakes.

• Causes breathing difficulties, irritates eyes and lungs

Methods of removal/treatment of Sulfur dioxide

Remove sulfur from fossil fuels before they are burnt

Desulfurisation - to remove SO2 from waste/flue/exhaust gases by treating it with calcium carbonate/oxide: CaCO3+SO2 —> CaSO3 (oxidised to CaSO4) + CO2

Use of calcium carbonate (powdered limestone) to reduce acidity and restore lakes and rivers polluted by acid rain.

Characteristics of Methane

CH4. Colourless and odourless.

Sources of Methane

Anaerobic bacterial decay of organic substances Waste gases from cattle (product of animal digestion)

Sources of Carbon dioxide (not a pollutant)

Complete combustion of carbon containing fuels Respiration Decomposition

Effects of Carbon dioxide and Methane

Greenhouse gases which causes global warming, resulting in environmental harm.

• Melting of polar ice caps leads to rise in sea levels and flooding of low-lying costal areas.

• More frequent and severe heat waves

• Increase in frequency and intensity of extreme weather

Methods of removal/treatment for Carbon dioxide

Plant more trees (not a long term solution) due to competing land uses.

Characteristics of unburnt hydrocarbon

Colourless and odourless/pungent due to fuel additives. (has, obviously, hydrogen and carbon as its constituent elements. ratio is variable.)

Sources of unburnt hydrocarbon

Incomplete combustion (i.e. insufficient oxygen available) of carbon-containing fuels/fossil fuels.

Effects of unburnt hydrocarbon

Eye and respiratory tract infections, leading to breathing difficulties. Reacts with nitrogen oxides in the presence of sunlight to form photochemical smog (brown haze), which also produced ozone, sulfur dioxide and nitrogen dioxide.

Methods of removal/treatment of unburnt hydrocarbon

Use a catalytic converter in cars: 2 C8H18 + 25 O2 —> 16 CO2 + 36H2O

Characteristics of ozone

Pale blue and pungent.

Sources of ozone (FYI)

Oxides of nitrogen reacts with unburnt hydrocarbons in the presence of sunlight Photochemical reactions in upper atmosphere: O2+O—>O3

Effects of Ozone (FYI)

Causes eye and respiratory tract infection, leading to breathing difficulties. Causes chest pains and coughing Slows down photosynthesis and plants —> damage crops

Methods of removal/treatment of ozone (FYI)

Reduce vehicle emissions of pollutants

Importance of ozone layer

Absorbs harmful ultraviolet radiation in the stratosphere from the sun which causes skin cancer, cataracts and genetic mutations.

How ozone layer is depleted

In presence of UV radiation, CFCs* decompose to form chlorine atoms which in turn react with ozone to form chlorine oxide (CIO) and oxygen. Chlorine oxide continues to react with another ozone molecule to form a chlorine atom. Chlorine atom continues to react with (attack) other ozone molecules in a chain reaction.

*chlorofluorocarbons

Definition of Carbon cycle

Mechanism that maintains the level of CO2 in the atmosphere (0.04%)

Describe ocean uptake (CO2)

Massive sink to trap dissolved CO2 for marine organisms. Eventually converted into calcium carbonate.

How does CO2 in the ocean become calcium carbonate? (stretch)

1. Dissolution of Carbon Dioxide in Seawater. When atmospheric carbon dioxide dissolves into ocean water, it reacts with water molecules to form carbonic acid. CO2+H2O<—>H2CO3

2. Dissociation into Bicarbonate and Carbonate Ions. Carbonic acid is unstable and quickly dissociates into hydrogen ions, bicarbonate ions, and carbonate ions H2CO3 <—> H+ + HCO3- HCO3- <—> H+ + CO3(2-)

3. Precipitation of Calcium Carbonate Marine organisms (such as corals, foraminifera, and mollusks) or inorganic processes combine dissolved calcium ions with carbonate ions, or utilize bicarbonate ions directly, to precipitate solid calcium carbonate: Using carbonate ions: Ca2+ + CO3(2-) —> CaCO3   Using bicarbonate ions (common in coral calcification): Ca2+ + 2HCO3- <—> CaCO3+CO2+H2O