Thursday, September 3, 2015

Nitrous Oxide Ban

On Saturday 29th August 2015, Brisbane's Couriermail reported that, "Supermarkets have removed nitrous oxide canisters from their shelves because of the alarming trend of people using the gas to get high".
Nitrous oxide, N2O, commonly known as "laughing gas", is found as an additive in food (E942). It has been used as an aerosol propellant in whipped cream canisters and cooking sprays, and has also been used as an inert gas to displace oxygen from food packages like potato chips to prevent the food from spoiling. The nitrous oxide canisters being removed from supermarket shelves refer to the small canisters used to re-charge re-usable whipped cream dispensers. Nitrous oxide is soluble in fats and oils so it is pumped into the fatty cream inside the dispenser where it dissolves. When the cream leaves the dispenser, the gas pressure inside the cream is greater than atmospheric pressure, so the nitrous oxide gas leaves the cream quickly, creating a foam. This "whipped cream" has about 4 times the volume of the original cream. However, if the whipped cream is left standing for some minutes, the gas pressure equilibrates with atmospheric pressure and the cream reverts to the "unwhipped" state.
Nitrous oxide has been the preferred choice for whipped cream dispensers because it does not react with the food and prevents it from spoiling. If air were used, the oxygen in the air would accelerate the rate of oxidation causing the cream to spoil. Carbon dioxide gas is not used because it would dissolve in the water present in the cream which would lower the pH and the cream would curdle.

In the laboratory, nitrous oxide can be produced by the thermal decomposition of ammonium nitrate (which is explosive!):
NH4NO3(s) → 2H2O(g) + N2O(g)
It can also be produced by heating a mixture of sodium nitrate and ammonium sulfate:
2NaNO3 + (NH4)2SO4 → Na2SO4 + 2N2O + 4H2O

Nitrous oxide has been used in dentistry as an anaesthetic for more than a century.
The chemistry of how nitrous oxide reacts in the body to produce a "high" is not well understood, but research continues.

Further Reading
Types of Chemical Reactions
Molecular Formula
Name and Formula of Covalent Compounds
Fats and Oils 
Solubility and Le Chatelier's Principle
Mass-mole Calculations
Mass and Moles in Chemical reactions 
Molar Volume of Gases 
Safety in the Laboratory

Suggestion Study Questions:
  1. Give the molecular formula for each of the following compounds: 
    • nitric oxide
    • nitrogen dioxide
    • nitrous oxide
    • dintrogen tetroxide
  2.  Name each of the following compounds:
    • CO2
    • CO
    • SO2
    • SO3
    • PCl3
    • PCl5
  3.  Draw possible Lewis (electron dot) structures for each of the following compounds:
    • nitric oxide
    • nitrogen dioxide
    • nitrous oxide
    • dintrogen tetroxide
  4.  "..whipped-cream has four times the volume of the original cream", describe what has happened to the density of the cream as a result of the "whipping" process.
  5. When I order an "iced-coffee" at a Cafe, they usually top it with some whipped-cream from a canister . Why does the whipped-cream float on top of the ice-coffee drink?
  6. If I don't the spoon the whipped-cream off the top of my "iced-coffee" I can stir it into the drink quite easily without it floating to the surface again. Explain why this happens.
  7. Explain what is meant by the term "fats and oils" when used by a Chemist and give examples.
  8. Most aerosol cans contain a warning to the effect that you should not heat the can. Explain what would happen if you heated a dispenser of whipped-cream containing nitrous oxide. 
  9. Imagine placing 10 grams of ammonium nitrate in a 500 mL sealed steel can, which you then (very irresponsively!) throw onto a bonfire.
    • Calculate the moles of ammonium nitrate in the can
    • Calculate the moles of nitrous oxide gas produced 
    • Calculate the volume of this number of moles of gas at 25oC
    • Predict what will happen to the sealed steel can in the bonfire. 
  10. Your company, "Ammo-nite", sells ammonium nitrate to farmers for use as a fertiliser. You have been asked to re-design the 100 g package so that it includes relevant safety precautions.

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