Alkanes, Alkenes and Ethanol Flashcards
Explain the terms homologous series, hydrocarbon, saturated, unsaturated, general formula and isomerism
Homologous series: a family of compounds that has the same general formula with similar properties because they have similar bonding.
Hydrocarbon: a compound containing hydrogen and carbon atoms only
Saturated: Molecules containing the maximum number of hydrogens for a given number of carbons
Unsaturated: molecule containing at least one double bond
Isomerism: compounds that have the same molecular formula but a different structure formulae
What is the general formula for Alkanes?
CnH2n+2
Recall the products of the complete and incomplete combustion of alkanes
Complete: carbon dioxide and water
Incomplete: carbon monoxide, soot and water
Describe the substitution reaction of methane with bromine to form bromomethane in the presence of UV light
Methane react with bromine in the presence of UV light. A hydrogen atom in the methane is replaced with a bromine atom from bromide, to form bromomethane and hydrogen bromide. If exposed to sunlight, it loses it’s brown colour.
What is the general formula for Alkenes?
CnH2n
Describe the addition reaction of alkenes with bromine,
When alkenes react with bromine, part of their double bond breaks and the electrons in it are used to joining to bromine atoms without any need for heat or a catalyst. The reaction is carried out in bromine water and the orange bromine water is decolourised when the tube is shaken. The product is 1,2-dibromoethane, a colourless liquid.
Describe the manufacture of ethanol by the hydration of ethane
Ethene and steam are reacted in temperatures of about 300 degrees and at 60-70atms. Phosphoric acid is used as a catalyst. Only a small portion of the ethene reacts. The ethanol produced is condensed as a liquid and the unreacted ethene is recycled through the process.
Describe the manufacture of ethanol by the fermentation
Yeast is added to a sugar or starch soliton and left in the warm for several days in anaerobic conditions. Enzymes in the yeast converts the sugar into ethanol and carbon dioxide.
The yeast is killed by more than 15% of alcohol in the mixture so it is impossible to make pure ethanol. The ethanol is purified by fractional distillation, which takes advantage of the difference in boiling points. The liquid distilling over at 78 degrees is 96% pure ethanol.
Evaluate the factors relevant to the choice of method used in the manufacture of ethanol
Fermentation uses renewable resources where as hydration uses finite resources, one day the oil will be used up so fermentation will be the way. Fermentation is a batch process so everything is mixed together in a reaction vessel and left for several days, this is slow as it takes several days and the quality of the product is very impure so it needs further processing. The hydration process is a continuous flow - a stream of reactants is constantly passed over the catalyst which makes it more efficient and a lot faster and it produces much purer ethanol.
Describe the dehydration of ethanol to ethene, using aluminium oxide
Ethanol vapour is passed over hot aluminium oxide in a test tube acting as a catalyst. It is then bubbled through cold water and is collected upwards as it is less dense than air.
