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The Challenge: Make Ice



The siphon pump turned out to be too weak to evaporate the methanol fast enough to achieve a temperature low enough to turn our water to ice. So we moved on to try making ice using ether as a cooling liquid. With a lower boiling point of 34.5°C it might just tip the balance between water and ice, even though the latent heat values show that more ether than methanol needs to be evaporated to remove the same amount of heat.

Ether can be made by heating ethanol with sulfuric acid at 140°C. (284°F)


How does this reaction happen?

At 140°C in the presence of sulfuric acid two molecules of ethanol are dehydrated (lose a molecule of water) to form ether. The sulphuric acid is regenerated and reused. Above about 160°C (320°F) ethene is produced instead, by loss of water from just one molecule of ethanol. Some sort of temperature control is needed.

As the ethanol and sulfuric acid reacted together ether vapor was given off. It needed to be cooled to condense it into liquid ether, so the apparatus was joined to a long tube that went through cold water to a receiver in a cold water bath. Because ether boils at 34.5°C (94.1°F) it needs to be cooled to condense it from a gas to a liquid and kept cool so it remains liquid. Below around 120°C (248°F) the reaction does not take place, above around 160°C ethene gas instead of ether is formed, so 140°C was chosen as a compromise between no reaction and the wrong reaction.

Heating ethanol with sulphuric acid diagram

Any experiment with ether must be carried out in the absence of any open flame.