Alcohols

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  • Created by: r98
  • Created on: 07-04-16 22:25
What's the general formula of an alcohol?
C(n)H(2n+1)OH.
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What's the shortened version of the general formula of an alcohol?
ROH
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What's the functional group of an alcohol?
-OH.
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What suffix is given to the -OH group?
'-ol'.
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What is the prefix of the alcohol functional group? When would it be used?
Prefix 'hydroxy-' is used if some other functional groups are present.
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If there is more than one -OH group, what do we use to say how many -OH groups there are?
We use di-, tri-, tetra-, etc.
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In alcohols, how many bonding pairs of electrons and how many lone pairs does the oxygen atom have?
2 bonding pairs and 2 lone pairs.
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What's the angle of the C-O-H bond?
105 (degrees).
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How are alcohols classified?
As primary (1 ), secondary (2 ) or tertiary (3 ) according to how many (R) groups are bonded to carbon that has the -OH group.
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In a primary alcohol, how R groups are attached to the carbon that has the -OH group?
1 R group.
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Where is the -OH group situated on a primary alcohol?
At the end of the chain.
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Which alcohol is methanol classified as?
Primary alcohol, even though is has no R groups.
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In a secondary alcohol, how R groups are attached to the carbon that has the -OH group?
2 R groups.
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Where is the -OH group situated on a secondary alcohol?
In the body of the chain.
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In a tertiary alcohol, how R groups are attached to the carbon that has the -OH group?
3 R groups.
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Where is the -OH group situated on a tertiary alcohol?
At a branch in the chain.
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What bonds can form between molecules, due to the -OH group?
Hydrogen bonds.
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Do alcohols have higher or lower melting, and boiling, points than alkanes of similar Mr? Why?
Alcohols have higher melting and boiling points, due to hydrogen bonding.
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How does hydrogen bonding affect short chain alcohols?
It makes them soluble in water, because hydrogen bonds can form between the -OH groups and water molecules.
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Why are alcohols important in industrial chemistry?
Because they're used as intermediates. They're easily made and easily converted into other compounds.
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What's methanol made from?
Methane (natural gas).
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What's the formula for ethanol?
C2H5OH
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What are some of the uses of ethanol?
It's used as a solvent in cosmetics (aftershave & perfumes), also used in the manufacture of drugs, detergents, inks and coatings.
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Industrially, how is ethanol made?
By reacting ethene (made from cracking crude oil) with steam, using a catalyst of phosphoric acid.
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How is the ethanol of alcoholic drinks produced?
By fermentation of sugars.
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How is ethanol produced from fermentation?
Carbohydrates from plants are broken down into sugars, and then converted into ethanol by the action of enzymes from yeast.
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Where do the carbohydrates (for fermentation) come from?
Sugar cane and sugar beet.
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What's the key step in the break down of sugar?
Anaerobic respiration.
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What is the equation for the break down of sugar?
C6H12O6(aq) -----> 2C2H5OH(aq) + 2CO2(g)
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What temperature is used for the production of ethanol by fermentation?
35 degrees celcius.
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Why is air kept out of the fermentation vessel?
To prevent oxidation of ethanol to ethanoic acid (acid in vinegar).
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What happens when the fermenting solution contains about 15% ethanol?
The enzymes are unable to function and fermentation stops.
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What is a biofuel?
A fuel derived or produced from renewable biological sources.
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Why can ethanol be described as a biofuel?
Ethanol made by fermentation is produced from renewable crops. It's mixed with petrol.
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Which method of making ethanol is renewable?
Ethanol made by fermentation.
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What does it mean when ethanol is described as a 'carbon-neutral fuel'?
The carbon dioxide released when it's burnt is balanced by the carbon dioxide absorbed by the plant from which it was originally obtained, during photosynthesis.
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Which method of producing ethanol can be classed as carbon neutral?
Ethanol made by fermentation.
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Why can it be argued that enthanol, made by fermentation, is not a carbon-neutral fuel?
Because there are other carbon costs associated witht the energy needed to transport crops and the fuel, and to process the crops.
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What is a renewable source of ethene?
Dehydration of ethanol made from sugar.
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If enough oxygen is available, what will alcohols burn completely to? What happens if there's not enough oxygen?
They burn completely to carbon dioxide and water. Otherwise incomplete combustion will happen, and carbon monoxide or carbon is produced.
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What is the equation for the complete combustion of ethanol?
C2H5OH(l) + 3O2(g) -----> 2CO2(g) + 3H2O(l)
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What are methylated spirits?
Ethanol with a small percentage of poisonous methanol added, to make it unfit for drinking.
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What are primary alcohols oxidised to?
Aldehydes.
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What's the general formula for an aldehyde?
RCHO.
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Can aldehydes be further oxidised? If so, what to?
Yes, they can be further oxidised to carboxylic acids.
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What's the general formula of a carboxylic acid?
RCOOH.
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What are secondary alcohols oxidised to?
Ketones.
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Whats the general formula of a ketone?
R2CO.
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Can ketones be oxidised further?
No.
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What are tertiary alcohols oxidised to?
They're not oxidised.
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Why are tertiary alcohols not oxidised?
It would need a C-C bond to break, rather than a C-H bond. This is the same reason for why ketones don't oxidise.
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How can the smell of aldehydes and ketones be described?
They have pleasant smells.
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What is the oxidising agent used to oxidise alcohols?
A solution of potassium dichromate, acidified with dilute sulfuric acid.
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During the oxidation of alcohols, what is the colour change of the oxidising agent?
The orange dichromate(VI) ions are reduced to green chromium(III) ions.
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How is ethanol oxidised to ethanal?
Using dilute acid and less potassium dichromate(VI) than is nedeed for complete oxidation. The mixture is heated gently in a reflux apparatus.
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How is ethanal seperated from ethanol?
Ethanal (boiling point of 294K) vaporises as soon as it's formed and distils off.
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What is often used to represent oxygen from the oxidising agent?
[O]
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What is the equation for the oxidisation of ethanol to ethanal?
CH3CH2OH(l) + [O] -----> CH3CHO(g) + H2O(l)
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How is ethanol oxidised to ethanoic acid?
Use conc. sulfuric acid and excess potassium dichromate(VI). Reflux the mixture for 20 minutes, the distil off the ethanoic acid (B.P. 391K).
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What does reflux mean?
It means that the vapour condenses and drips back into the reaction flask.
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What is the equatoin for the oxidisation of ethanol to ethanoic acid?
CH3CH2OH(l) + 2[O] -----> CH3COOH(g) + H2O(l)
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What is the name of the C=O group that aldehydes and ketones have?
The carbonyl group.
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Where is the carbonyl group in an aldehyde?
It's at the end of the chain.
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Where's the carbonyl group in a ketone?
It's in the body of the chain.
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What suffix is used to name aldehydes?
-al.
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What suffix is used to name ketones?
-one.
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What do both the tests, used to tell aldehydes and ketones apart, involve?
Both tests involve gentle oxidation.
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What is one test for distinguishing between aldehydes and ketones? What reagent is used?
Tollens' (silver mirror) test. Tollens' reagent (a solution of silver nitrate in aqueous ammonia) is used.
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How does Tollens' reagent react with aldehydes? how about with ketones?
It oxidises aldehydes but has no affect with ketones.
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What happens to the ions in Tollens' reagent when it oxidises an aldehyde?
Tollens' contains colourless silver(I) complex ions which are reduced to metallic silver, as the aldehyde is oxidised.
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What would you expect to see when Tollens' reagent reacts with an aldehyde? How about a ketone?
With an aldehyde - silver mirror is formed. With a ketone - no visible change.
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What is another test that can be used to distinguish between aldehydes and ketones? What reagents are used?
The Fehling's/ Benedict's test. Fehling's reagent or Benedict's reagent.
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What ions do both, Fehling's and Benedict's reagents, contain? How do they affect aldehydes and ketones?
They both contain blue copper(II) complex ions which will oxidise aldehydes but not ketones.
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What observations can be made when an aldehyde is warmed with Fehling's or Benedict's solution? How about when a ketone is warmed with it?
With an aldehyde - the blue solution gradually changes to a brick red precipitate of copper(I) oxide. With a ketone - no visible change.
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What are elimination reactions?
Reactions in which a small molecule leaves the parent molecule.
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During an elimination reaction of water, what is the small molecule that's removed?
It's always water, made from the -OH group and a hydrogen atom from the carbon next to the -OH group.
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Since the elimination reactions of alcohols involve a water molecule being removed, how can we describe it?
They're always dehydration reactions.
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What reagents can be used to dehydrate alcohols?
Excess hot concentrated sulfuric acid, or by passing the vapours of the alchol over heated aluminium oxide, or using phosphoric(V) acid.
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What is formed when an alcohol is dehydrated?
An alkene.
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What may be produced when longer chain or branched alcohols are dehydrated?
It may produce a mixture of alkenes, including ones with Z and E isomerism.
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What's the shortened version of the general formula of an alcohol?

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Card 3

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Card 4

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What suffix is given to the -OH group?

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Card 5

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