2e) Oxygen and oxides

Air

• 78% Nitrogen

• 21% Oxygen

• 0.93% Argon and other noble gases

• 0.04% carbon dioxide

• Variable amounts of water vapour

• Variable amounts of pollutant gases

Oxygen

• Extracted from air by fractional distillation

• If air is cooled down, at -183°C oxygen condenses into a liquid (at -196°C Nitrogen condenses too)

Burning magnesium

magnesium + oxygen magnesium oxide

reactants product

+

Heating other metals

Heating copper in air

Burning copper

copper + oxygen copper oxide

reactants product

+

Copper and air

Iron and air

Iron and air

The amount the water rises

indicates the percentage

oxygen in the air

Methane and oxygen

methane + oxygen carbon dioxide + water

CH4(g) + 2O2(g) CO2(g)+ 2H2O(g)

Carbon and oxygen

Carbon burns producing carbon dioxide and water

C + O2 CO2 + 2H2O

Sulphur dioxide SO2

Produced by burning sulphur (or burning fossil fuels)

S(l) + O2(g) SO2(g)

In water

Dissolves to form sulphurous acid

SO2(g) + H2O(l) H2SO3(aq)

With an alkali

Forms a sulphite

SO2 + 2NaOH Na2SO3 + H2O

Carbon dioxide

Preparing carbon dioxide

Acid + carbonate salt + water + carbon dioxide

2HCl + CaCO3 CaCl2 + H2O + CO2

In water

Dissolves to form carbonic acid

CO2(g) + H2O (l) H2CO 3(aq)

pH 5.5

In alkali

H2CO 3(aq) + 2NaOH(aq) Na2CO3(aq) + 2H2O(l)

acid + base salt + water

Uses of carbon dioxide

Fizzy drinks. The higher the pressure, the more soluble the gas becomes.

So what happens when the pressure

is released?

Uses of carbon dioxide

Fire extinguishersHow does it

work?

Uses of carbon dioxide

Dry ice (actually it’s condensed water vapour that you can see.)

Oxides of nitrogen

Nitrogen is generally an unreactive gas, and needs fairly extreme conditions to get it to react with oxygen

Nitric oxide, NO

Lightning brings about the direct union of nitrogen and oxygen in the air to produce small amounts of nitric oxide, as does the high temperatures produced in car engines.

Nitric oxide, NO

It is a toxic air pollutant, often linked with asthma and allergic responses

Nitrogen dioxide, NO2

In the presence of excess oxygen, nitric oxide, NO, will be converted to nitrogen dioxide,NO2. Nitrogen Dioxide is a reddish brown, toxic gas at room temperature. NO2 condenses to a brown liquid, but freezes to a colourless solid.

Nitrogen dioxide, NO2

Nitrogen Dioxide has been used as a catalyst in certain oxidation reactions; as a nitrating agent for organic compounds; as an oxidizing agent; as a rocket fuel; and as a flour bleaching agent

Nitrous oxide, N2O

Formed when ammonium nitrate, NH4NO3, is heated. A colourless gas with a pleasing odour and sweet taste, is used as an anesthetic for minor operations, especially in dentistry.

You don’t need to know

about this!

Nitrous oxide, N2O

It is called laughing gas because of its intoxicating effect. It is alsowidely used as a propellant in aerosol cans of whipped cream!

A reminder!

Rusting

Rust is a form of iron oxide. It has water bonded loosely to it. It is called hydrated iron oxide

In order for iron to rust

Both air and water’s a must,

Air alone won’t do

Without water there too,

So protect it, or get a brown crust!

It’s actually the oxygen in air

Protecting from rust

Protecting from rust

Protection method How it works

Paint Barrier

Vaseline/oil Barrier

Silicone Barrier

Zinc (Galvinising) Sacrificial

Sacrificial protection

Sacrificial protection

Zinc is electrically connected to the iron. Any water or oxygen reacts with the zinc (or magnesium) instead of the iron. Coating in zinc is called galvanization and it works even when the zinc coating is scratched.