3. Organic Chemistry Flashcards
What is the general formula for alkanes?
Alkanes is a homologous series with the formula CnH2n +2.
Define:
homologous series hydrocarbon saturated unsaturated general formula isomerism.
Compounds in the same homologous series have the same general formula and similar chemical properties.
A hydrocarbon is a compound made up only of hydrogen and carbon.
Saturated means something has bonded as many time as possible. Unsaturated means that more bonds can be made.
General formula is the most simplified the ratio of molecules can be.
Isomers have the same general formula but different structures.
What are the products of the complete and incomplete combustion of alkanes?
Complete combustion gives carbon dioxide and water.
Incomplete combustion gives carbon monoxide and water.
describe the substitution reaction of methane with bromine to form bromomethane in the presence of UV light.
In UV light bromine and methane will form bromomethane:
CH4 + Br2 –> CH3Br + HBr
What has happened in this reaction is a bromine has taken the place of a hydrogen (substitution.)
What is the general formula for an Alkene?
All compounds in the homologous group alkenes have the general formula CnH2n.
describe the addition reaction of alkenes with bromine, including the decolourising of bromine water as a test for alkenes
An alkene will make its double bond into a single bond, to bond to two bromines. Bromine is added to the molecule. The product made is colourless. When alkenes are put in bromine water it turns from brown to colourless (a good way of testing for alkenes.)
For example:
C2H4(g) + Br2 (aq) → C2H4Br2 (aq)
describe the manufacture of ethanol
ethanol is produced by ethene and steam being passed over a phosphoric acid catalyst at a temperature of about 300°C and a pressure of about 60–70 atm
C2H4 (ethene) + H2O (steam) > C2H5OH (ethanol)
This reaction takes place at a high pressure (60-70 atm) and a high temperature (300) to make the reaction happen very quickly. Phosphoric acid also speeds up the reaction as it is a catalyst.
describe the manufacture of ethanol by the fermentation of sugars, for example glucose
Ethanol can be made by the anaerobic respiration of microorganisms.
glucose > ethanol + carbon dioxide
This happens at 30 degrees.
evaluate the factors relevant to the choice of method used in the manufacture of ethanol (fermentation and hydrating)
Fermentation
Cane sugar widely avalible/ cheap/ renewable
Slow process
Impurities in the product
Done in batches
Hydrating (ethene and steam)
Crude oil (cracked to make ethene) expensive/ non-renewable
Fast process
Pure product
Continuous reaction
describe the dehydration of ethanol to ethene, using aluminium oxide.
C2H5OH > C2H4 + H2O
ethanol > ethene + water
aluminium oxide is the catalyst for this reaction.
