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a-level chemistry > 11 - alcohols > Flashcards

11 - alcohols Flashcards

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1
Q

What is the alcohol functional group?

A

OH (Hydroxyl group)

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2
Q

What is the general formula of alcohols?

A

C~n H~(2n + 2) O

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3
Q

When is an alcohol a primary alcohol?

A

When the OH is only attached to one alkyl group.

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4
Q

When is an alcohol secondary?

A

When the carbon that the OH is on is attached to two alkyl groups

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5
Q

When is an alcohol tertiary?

A

When the carbon that the OH is on is attached to three alkyl groups

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6
Q

What state does ethanol have at room temperature?

A

liquid

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7
Q

Why do alcohols have a higher boiling point than alkanes?

A

The OH group has a dipole (H has delta positive)

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8
Q

What is volatility?

A

How easily a substance evaporates

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9
Q

How does volatility change as boiling point changes?

A

Volatility decreases as boiling point increases

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10
Q

What is the volatility of alcohols like compared to alkanes and why?

A

alcohols have a low volatility compared to alkanes

Due to hydrogen bonds

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11
Q

Do alcohols dissolve in water?

Explain

A

They do dissolve in water

Because they are polar due to their hydrogen bonds

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12
Q

How does chain length affect solubility and why?

A

As chain length increases, solubility decreases

Because hydrocarbon chain is not polar and can’t make hydrogen bonds with water

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13
Q

What is an oxidising agent?

A

A reagent which provides the oxygen in a reaction

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14
Q

In the oxidation of alcohols

What is the oxidising agent?

A

Acidified potassium dichromate

H+ | K~2 Cr~2 O~7

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15
Q

What are the 2 oxidation reactions that can be done on primary alcohols?

A

Distillation

Reflux

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16
Q

What is formed when primary alcohols are oxidised by distillation?

A

Aldehyde and water

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17
Q

How do you draw aldehydes?

A

One of the END carbons must have a C=O instead of one if its C-H bonds

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18
Q

How do you write the equation for the oxidation of an alcohol by distillation?

A

Draw out the alcohol

Then put + [O]

Then draw the reaction arrow with H+ | K~2 Cr~2 O~7 above it and “distillation” below it

Draw the aldehyde with the same number of carbons as the alcohol

Then put + H~2 O

19
Q

What are the observations of all primary alcohol oxidation reactions?

A

Acidified potassium dichromate goes from orange to green

20
Q

What is the naming system for aldehydes?

A
  • al suffix

e. g. Ethanol goes to ethanal

21
Q

What is the aldehyde functional group?

A

CHO

22
Q

What is produced when alcohols are oxidised by reflux?

A

Carboxylic acid and water

23
Q

What type of alcohol do you need to use to get carboxylic acids?

A

A primary alcohol must be used under reflux

24
Q

How do you draw carboxylic acids?

A

Put a C-OH

And C=O

On the end carbon

25
Q

How do you write the equation for reflux oxidising alcohols?

A

Draw the alcohol

Put + 2[O]

Draw the reaction arrow with H+ | K~2 Cr~2 O~7 above and reflux below

Draw the carboxylic acid

Write + H~2 O

26
Q

What is the functional group of carboxylic acids?

A

COOH

27
Q

What is the observation when oxidising secondary alcohols?

A

Still colour change from orange to green

28
Q

What is a ketone?

A

Like an aldehyde but the C=O is on a middle carbon (not end carbon)

when finding an isomer of a ketone, you can’t put the C=O on an end carbon because that would be an aldehyde

29
Q

What is the functional group for ketones?

A

RCOR

R just means other stuff (usually an alkyl group)

30
Q

What are the types of reaction for oxidising secondary alcohols?

A

There’s only one

Applying heat

31
Q

How do you name ketones?

A
  • one is the suffix

e. g. pentan-2-one

32
Q

How do you write the reaction for oxidation of secondary alcohols?

A

Draw an alcohol where the OH isn’t on an end carbon

Put + [O]

Put a reaction arrow with H+ | K~2 Cr~2 O~7 above it and “heat” below it

Draw the ketone

Put + H~2 O

33
Q

Describe the dehydration of alcohols

A

An alcohol is heated with a reagent of CONCENTRATED H~2 SO~4 and heat

An alkene and water is produced

This is an elimination reaction

34
Q

With dehydration of alcohols, what is different when secondary alcohols are used?

A

2 different alkenes are produced

With the double bond on the left of where the OH was

And with the double bond on the right of where the OH was

35
Q

What is the basic idea of what happens in an alcohol substitution reaction?

A

The OH of the alcohol is substituted by a halogen to form a haloalkane

36
Q

What are the conditions and reagents of alcohol substitution?

A

Reflux the alcohol

With sulphuric acid and sodium halide

(The halide contains the halogen that we want in the haloalkane)

37
Q

Why is a sodium halide used in substitution of alcohols?

A

The hydrogen halide on its own doesn’t work for some reason

38
Q

What is the first reaction which happens in substitution of alcohols?

A

NaX + H~2 SO~4
–>
NaHSO~4 + HX

Where X is the halogen

39
Q

What is the second reaction which happens in substitution of alcohols?

Use ethanol as the alcohol

A

C~2 H~6 O + HX
–>
C~2 H~5 X + H~2 0

Where X is the halogen

40
Q

What is the overall reaction of alcohol substitution?

Use propanol as the alcohol and chlorine as the halogen

A

C~3 H~8 O + NaCl + H~2 SO~4
–>
C~3 H~7 Cl + NaHSO~4 + H~2 O

41
Q

What does a nitrile contain?

A

A triple bond

42
Q

How do you draw cyanide?

A

C triple bond N

Put a lone pair on the C

43
Q

Why are the boiling points of branched alcohols less than boiling points of straight chain alcohols?

2 marks

A

Less points of contact between branched alcohols

So less energy required to break London forces in branched alcohols

a-level chemistry (25 decks)

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