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Chemistry > Chapter 14 - Alcohols > Flashcards

Chapter 14 - Alcohols Flashcards

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1
Q

What is the functional group of alcohols ?

A
  • OH

Hydroxyl group

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2
Q

Are alcohols polar and why ?

A
  • Alcohols are polar due to the presence of the O-H bond

- The OH bond is polar because of a difference in electronegativity of O and H

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3
Q

What is a primary alcohol ?

A

The C atom that is attached to the OH is attached to 1 alkyl group and 2 H atoms

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4
Q

What is a secondary alcohol ?

A

The C atom that is attached to the OH is attached to 2 alkyl groups and 1 H atom

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5
Q

What is a tertiary alcohol ?

A

The C atom that is attached to the OH is attached to 3 alkyl groups and 0 H atoms

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6
Q

What kind of alcohol is methanol (exception) ?

A

It is a primary alcohol, it is the only exception and is quite misleading

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7
Q

Why do alcohols have a higher boiling point/melting point ?

A
  • They have a higher boiling point due to the hydrogen bond that can be formed because of the OH group.
  • This requires more energy to overcome and therefore increases its boiling point and melting point
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8
Q

Why do alcohols with few carbon atoms have much higher boiling points than alkanes with the same number of carbon atoms ?

A
  • Less carbon atoms means that the OH bond has a stronger influence as it requires the most energy to break compared to the carbon bonds
  • More carbon atoms means that the bond enthalpy for the entire thing is more shared out and the OH bond has less of an influence
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9
Q

What is meant by the volatility ?

A

How easily it can change into a gas

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10
Q

How do alcohols and alkanes compare in volatility ?

A

Alcohols with the same number of carbon atoms as an alkane will be less volatile

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11
Q

Why are alcohols less volatile than alkanes, when they have the same number of carbon atoms ?

A
  • In the liquid state, the hydrogen bonds hold the alcohol molecules together. These bonds must be broken in order to change the liquid alcohol into gas.
  • This requires more energy compared to alkanes therefore they have a lower volatility
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12
Q

Why are alcohols soluble in water ?

A

The polar OH bonds forms hydrogen bonds with the water molecules

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13
Q

As hydrocarbon chain increases, how does solubility of alcohols change ?

A

It decreases as the OH groups has a smaller influence and solubility shifts to that of the alkanes

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14
Q

What are the products of the combustion of alcohol ?

A
  • Carbon dioxide

- Water

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15
Q

What is used to oxidise alcohols ?

A

Potassium dichromate

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16
Q

What is the formula for potassium dichromate ?

A

K2Cr2O7

17
Q

What is acidified potassium dichromate ?

A
  • K2Cr2O7/H2SO4

- Potassium dichromate that has been put into acid, leading to it being acidified

18
Q

What are the two forms of chromium in oxidation reactions ?

A
  • Dichromate(VI) ions that are orange, Cr2O7 (2-)

- Chromium(III) ions that are green, Cr (3+)

19
Q

What indicates that the alcohol has been oxidised ?

A

The change in colour of potassium dichromate from orange to green

20
Q

Which two products can be formed from the oxidation of primary alcohols ?

A
  • Aldehydes

- Carboxylic acids

21
Q

How are aldehydes prepared from the oxidation of primary alcohols ?

A

Gentle heating of primary alcohols with acidified potassium dichromate

22
Q

What measure is taken to ensure no carboxylic acid is made ?

A

Aldehyde is distilled out of the mixture as it forms to prevent any further reaction

23
Q

How are carboxylic acids prepared from the oxidation of primary alcohols ?

A

Primary alcohol is heated strongly under reflux with an excess of acidified potassium dichromate

24
Q

Why is it under reflux for carboxylic acid preparation ?

A
  • To ensure any aldehyde initially formed also undergoes oxidation to the carboxylic acid
  • Any aldehyde formed will drip backdown into the flask and it will carry on undergoing oxidation
25
Q

What product is formed from the oxidation of secondary alcohols ?

A

Ketones

26
Q

How are ketones prepared from the oxidation of secondary alcohols ?

A

Heated under reflux with acidified potassium dichromate

27
Q

What product is formed from the oxidation of tertiary alcohols ?

A

Tertiary alcohols do not undergo oxidation reactions

28
Q

What is dehydration ?

A

Any reaction in which a water molecule is removed from the starting material

29
Q

What are the conditions of a dehydration reaction ?

A

Alcohol is heated under reflux in the presence of concentrated sulphuric acid or phosphoric acid (H3PO4)

30
Q

What are the products of the dehydration of an alcohol ?

A

An alkene and water

31
Q

Alcohols react with hydrogen halides to form what ?

A

Haloalkanes and water

32
Q

What are the conditions of a halogen substitution reaction of an alcohol ?

A
  • Alcohol is heated under reflux with sulphuric acid (H2SO4) and a sodium halide, the hydrogen halide is formed in situ
  • The hydrogen halide then reacts to form the haloalkane and water

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