alcohols Flashcards
what is the general formula for an alcohol? (1)
CnH2n+1OH
what is the prefix or suffix given for alcohols? (2)
prefix; -ol
suffix; (given when there are other functional groups present) -hydroxy
what is the main ingredient in antifreeze? (1)
ethane-1,2 -diol
what is the shape of an alcohol? (1)
in alcohols, the oxygen has two bonding pairs of electrons and two lone pairs. The C-O-H angle is about 105 degrees because the 1o9.5 degree angle of the perfect tetrahedron is ‘squeezed down’ by the presence of the lone pairs.
how are alcohols classified? (3)
alcohols are classified as primary (1 degree), secondary (2nd degree) and tertiary (3rd degree)
what is a primary alcohol? (1)
in a primary alcohol the carbon with the -OH has one R group (and therefore 2 hydrogen atoms)
what is a secondary alcohol? (1)
in a secondary alcohol, the -OH group is attached to a carbon with two R groups (and therefore one hydrogen atom)
what is a tertiary alcohol? (1)
tertiary alcohols have three R groups attached to the carbon that is bonded to the -OH (has no hydrogen atoms)
what are the physical properties of an alcohol? (3)
-high melting and boiling points
-alcohols with short hydrocarbon chains are soluble in water
-alcohols with long hydrocarbon chains are insoluble in water
why do alcohols have high melting and boiling points? (1)
the -OH group in alcohols means that hydrogen bonding occurs between the molecules.
why are short alcohol chains soluble in water? (1)
the -OH group in alcohols can hydrogen bond to water molecules, but the non-polar chain cannot - the hydrogen bonding predominates
why are long alcohol chains insoluble in water? (1)
the non-polar hydrocarbon chain dominates and the alcohols become insoluble in water
what is the formula for ethanol? (1)
C2H5OH
how is ethanol made industrially? (1)
by reacting ethene (made by cracking crude oil) with steam.
what catalyst is used in the production of ethanol? (1)
phosphoric acid
what are the two ways in which ethanol can be made? (2)
-cracking and hydration
-fermentation and distillation
what is meant hydration? (1)
water is added across the double bond.
what happens during fermentation? (1)
carbohydrates from plants are broken down into sugars and then converted into ethanol by the action of enzymes from yeast.
what do the carbohydrates used in fermentation come from? (1)
the carbohydrates come from crops such as sugar cane and sugar beet
what is the key step in the breakdown of sugar? (1)
a process called anaerobic respiration
what is the rate of anaerobic respiration in the breakdown of sugars effected by? (1)
temperature, its is slow temperatures but the enzymes are made ineffective if the temperature is too high.
what is the best temperature for fermentation of ethanol? (1)
a compromise temperature of 35 degrees is used
why does fermentation occur in a sealed vessel? (1)
air is kept out of the fermentation vessels to prevent oxidation of ethanol to ethanoic acid (the acid in vinegar)
what are the differences between the two methods of ethanol production? (4)
rate of reaction;
-C/H: Fast
-F/D: Slow
type of process;
-C/H: Continuous
-F/D: Batch
purity;
-C/H: Essentially pure
-F/D: aqueous solution of ethanol is produced
what is produced in the complete combustion of alcohols? (1)
alcohols burn completely to carbon dioxide and water if there is enough oxygen available.
what is produced in the incomplete combustion of alcohols? (1)
carbon dioxide or carbon is produced
what is an elimination reaction? (1)
elimination reactions are ones in which a small molecule leaves the parent molecule, in the case of alcohols this molecule is always water. (are always dehydrations)
how can alcohols be dehydrated? (2)
alcohols can be dehydrated with excess hot concentrated sulfuric acid or by passing their vapours over heated aluminium oxide.
what is produced from the dehydration of an alcohol? (1)
an alkene is produced
what is combustion usually? (1)
combustion is usually complete oxidation
what are primary alcohols normally oxidised to? (1)
primary alcohols are oxidised to aldehydes, aldehydes can be further oxidised to carboxylic acids
what are secondary alcohols oxidised to? (1)
secondary alcohols are oxidised to ketones, ketones are not oxidised further.
what are tertiary alcohols oxidised to? (2)
tertiary alcohols are not easily oxidised because oxidation would need a C-C bond rather than a C-H bond
what experiment can be used to oxidise aldehydes and ketones? (1)
a solution of potassium dichromate, acidified with dilute sulfuric acid (oxidising agent)
what are the similarities between aldehydes and ketones? (1)
both have the C=O group (carbonyl group)
-aldehydes; at the end of the chain
-ketones; the body of the chain
what are the two tests which can distinguish a ketone and aldehyde? (2)
-the tollens test
-the fehlings test
what is the tollens test? (2)
its a solution of silver nitrate in aqueous ammonia, it oxidises aldehydes but has no effect on ketones. A deposit of metallic silver is formed on the inside of the test tube
what is the fehlings test? (2)
the blue solution gradually changes to a brick red precipitate of copper oxide.
