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AQA A Level Chemistry > 3.5 Alcohols > Flashcards

3.5 Alcohols Flashcards

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1
Q

What is the functional group of an alcohol ?

A

Hydroxide (OH-)

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2
Q

What is the general formula of an alcohol ?

A

CnH2n+1OH

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3
Q

What kind of intermolecular forces do alcohols have ?

A

•Van der waals
•Hydrogen bonds (OH)

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4
Q

How do alcohols mp and bp compare do other hydrocarbons ?

A

Higher, as alcohols have Hydrogen bonding whereas other molecules like alkanes do not

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5
Q

Are alcohols soluble in water ? Why does solubility depend on chain length ?

A

•Short chains are soluble as the OH has slight charges
•Long chains are insoluble as the non polar C-H take priority.

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6
Q

What makes an alcohol primary ?

A

When the carbon that contains the OH group is only bonded to one other carbon.

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7
Q

What makes an alcohol secondary ?

A

When the carbon containing the OH group is bonded to two other carbons.

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8
Q

What makes an alcohol tertiary ?

A

When the carbon containing the OH group is bonded to 3 other carbons.

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9
Q

How can ethanol be made from a product of crude oil fractionation ?

A

Hydration of ethene via electrophilic addition (H2PO4 catalyst).

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10
Q

What are the advantages and disadvantages of producing ethanol via hydration of ethene ?

A

Advantages - fast, continuous process with high yield purity
Disadvantages - non renewable as ethene is obtained from crude oil.

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11
Q

How can ethanol be made from fermentation ?

A

Plant carbohydrates are broken down and fermented by enzymes in yeast -> ethanol.

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12
Q

What conditions are needed for fermentation of plant carbohydrates to take place

A

•Enzymes in yeast as a catalyst
•35 degrees C
•anaerobic conditions.

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13
Q

Write an equation for the fermentation of glucose

A

C6H12O6 (aq) -> 2C2H5OH + 2CO2.

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14
Q

What are the advantages and disadvantages of obtaining ethanol from fermentation ?

A

Advantages - renewable
Disadvantages - slow, batch process, enzymes denature at low alcohol conc so is not pure and requires distilling.

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15
Q

Define carbon neutral

A

No net CO2 emissions into the atmosphere.

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16
Q

Explain why the combustion of ethanol as a fuel is described as neutral ?

A

As the CO2 released in fermentation and combustion is the same as what is taken in during photosynthesis.

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17
Q

Why, in actuality, is using fermented ethanol as a fuel not carbon neutral ?

A

As other costs, such as that of transport, affect neutrality.

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18
Q

What an equation for the combustion of ethanol.

A

C2H5OH + 3O2 -> 2CO2 + 3H2O

19
Q

What is an elimination reaction ?

A

The removal of a smaller molecule from a larger one.

20
Q

What group leaves the parent molecule in elimination reactions of alcohols ?

A

The OH and a H to form water

21
Q

What physical conditions are needed for the elimination reactions of alcohols to alkenes ?

A

Excess hot concentrated sulphuric acid or pass over hot aluminium oxide.

22
Q

Describe the mechanism for the dehydration of ethanol

A
23
Q

Describe a method for dehydration of ethanol in a lab

A

Ethanol is heated with an excess of concentrated sulfuric acid at a temperature of 170°C, all in a boiling tube

24
Q

What forms if you partially oxidise an alcohol ?

A

An aldehyde.

25
Q

What conditions are needed to partially oxidise a primary alcohol ?

A

Dilute sulphuric acid, potassium dichromate, distill product as it is produced, gentle heating.

26
Q

Write an equation for the partial oxidisation of ethanol

A

CH3CH2OH (l) + [O] -> CH3CHO (g) + H2O (l)

27
Q

What is formed if you fully oxidise an alcohol ?

A

A carboxylic acid

28
Q

What conditions are needed for the complete oxidation of an alcohol ?

A

Concentrated sulphuric acid, potassium dichromate, reflux for 20 mins, strong heating.

29
Q

Write an equation for the full oxidation of ethanol.

A

CH3CH2OH + 2[O] -> CH3COOH + H2O

30
Q

What forms if you oxidise a secondary alcohol ?

A

A ketone

31
Q

Why can a ketone not be oxidised and why can tertiary alcohols not be oxidised ?

A

As a carbon-carbon bond would have to break and that requires too much energy

32
Q

What conditions are needed for the oxidation of a secondary alcohol ?

A

Concentrated sulphuric acid, potassium dichromate, reflux for 20 mins, strong heating

33
Q

Write an equation for the oxidation or propan-2-ol

A

CH3CHOHCH3 + [O] -> CH3COCH3 + H2O.

34
Q

What is an aldehyde ? What is it’s functional group ?

A

A molecule with a C=O group at the end of a carbon chain.

35
Q

What is a ketone ? What is it’s functional group ?

A

A molecule with a C=O group in the middle of a carbon chain.

36
Q

What is a carboxylic acid ? What is it’s functional group ?

A

Molecule with a COOH group at the end of a carbon chain
Carboxyl group (COOH) consists of carbonyl (C=O) and hydroxyl (OH)

37
Q

What does the Tollens test give a positive result for ?

A

Aldehydes

38
Q

What molecule in Tollens Reagent reacts with aldehydes to give a positive result ?

A

Silver nitrate in NH3
This oxidises aldehydes but not ketones
Complex silver (I) ions reduced to Ag(s), forms a mirror.

39
Q

How do you carry out the Tollens test ?

A

Add equal volumes of reactant and tollens solution to a test tube
Leave in water bath for 10 mins and observe changes.

40
Q

What does the fehlings solution test for ?

A

Aldehydes

41
Q

What is in Fehlings solution ? How does this react with the solution being tested ?

A

Copper (II) complex ions - a slight oxidising agent
The Cu2+ is reduced to Cu+ (brick red)

42
Q

What conditions do you need to do the Fehlings solution test

A

Heat

43
Q

What result do aldehydes and ketones give the Fehlings test

A

Aldehydes - brick red ppt forms
Ketone - no reaction.

AQA A Level Chemistry (26 decks)

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