C14 - Alcohols Flashcards

1
Q

What is the functional group of an alcohol?

A

-OH (hydroxyl group)

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2
Q

What is the general formula of an alcohol

A

CnH2n+1OH

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3
Q

How do you name an alcohol

A

1) Suffix is -ol (number before ol)
2) Identify longest carbon chain
4) Identify and number any alkyl groups

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4
Q

What are the physical properties of alcohols compared to alkanes?

A

-Less volatile
-Higher melting and boiling points
-Greater solubility

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5
Q

Do the differences between alcohols and their corresponding alkane increase or decrease as the chain length increases?

A

Decrease

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6
Q

Why does the difference between alcohols and alkanes decrease?

A

-OH group becomes relatively smaller

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7
Q

Why do alcohols have higher boiling points than alkanes?

A

-Alkanes have non-polar bonds and are therefore non-polar
-Intermolecular forces between non-polar molecules are weak London forces
-Alcohols have a polar O-H bond, therefore, they are polar molecules
-Intermolecular forces will be weak London forces and string hydrogen bonds

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8
Q

How do you draw a hydrogen bond

A
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9
Q

What is a hydrogen bond?

A

Strong dipole-dipole attraction between an electron deficient hydrogen atom on a highly electronegative atom containing N/O/F

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10
Q

What is volatility?

A

Ease at which a liquid turns into a gas
Increases with boiling point

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11
Q

What is the difference in volatility of alkanes and alcohols?

A

Hydrogen bond requires more energy to overcome than weak London forces
Alcohols have lower volatility

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12
Q

Why are alcohols soluble in water

A

Polar OH group forms hydrogen bonds with water

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13
Q

What happens to solubility of alcohols as chain length increases?

A

Decreases

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14
Q

What can alcohols be classified as?

A

Primary
Secondary
Tertiary

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15
Q

What is a primary alcohol?

A

Alcohol in which the OH group is attached to a carbon atom that is attached to two or hydrogen atoms (one alkyl group)

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16
Q

What is a secondary alcohol?

A

Alcohol where the OH group is attached to a carbon atom attached to one hydrogen atom and two alkyl groups

17
Q

What is a tertiary alcohol?

A

Alcohol where the OH group is attached to a carbon atom attached to no hydrogen atom and three alkyl groups

18
Q

Complete combustion of alcohols equation

A

CnH2n+1OH + O2 —> CO2 + H2O

19
Q

Incomplete combustion of alcohols equation

A

CnH2n+1OH + O2 —> CO + H2O

20
Q

What is the oxidising agent for primary and secondary alcohols?

A

Potassium dichromate (VI), acidified with dilute sulfuric acid
K2Cr2O7 + H2SO4 (aq)

21
Q

What colour change is seen if the alcohol is oxidised?

A

Orange to green

22
Q

What happens to dichromate (VI) ions during the colour change?

A

Cr2O7(2-) —> Cr(3+)
Dichromate (VI) ions —> Chromium (III) ions
Orange —> Green

23
Q

What are primary alcohols oxidised too?

A

Aldehydes / carboxylic acids

24
Q

How do you prepare aldehydes?

A

-Primary alcohols
-Acidified potassium dichromate
-Heat and distil (prevents further reaction with oxidising agent)
-Colour change from orange to green

25
Q

Equation of butan-1-ol to form an aldehyde

A
26
Q

Preparation of carboxylic acid

A

-Primary alcohols
-Excess of acidified potassium dichromate (VI) (ensures all alcohol and aldehyde is oxidised)
-Heat and reflux
-Colour change from orange to green

27
Q

Equation for oxidation of butan-1-ol to form a carboxylic acid

A
28
Q

What do secondary alcohols oxidise to produce?

A

Ketones

29
Q

Preparation of ketones

A

-Secondary alcohols
-Acidified potassium dichromate (VI)
-Heat and reflux (ensures reaction goes to completion)
-Colour change from orange to green

30
Q

Equation for oxidation of secondary alcohols

A
31
Q

What does oxidising tertiary alcohols produce?

A

Do not undergo oxidation reactionsn

32
Q

What is dehydration?

A

Elimination reaction in which water is removed from a saturated molecule to make an unsaturated molecule

33
Q

Dehydration of alcohols - conditions and products

A

Alcohol —> alkene
Heat and reflux
Acid catalyst - H2SO4 / H3PO4

34
Q

Substitution reaction of alcohols

A

Alcohols + hydrogen halide —> haloalkane
Heat and reflux with sulfuric acid

NaBr + H2SO4 —> NaHSO4 + HBr
Alcohol + HBr + H2SO4 —> Haloalkane + NaHSO4 + H2O