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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.