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A level Chemistry OCR A > 14.2 Reactions of Alcohols > Flashcards

14.2 Reactions of Alcohols Flashcards

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1
Q

What types of reactions can alcohols undergo?

A

COMBUSTION

OXIDATION

SUBSTITUTION

DEHYDRATION

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2
Q

What is the general equation for combustion of an alcohol?

A

Alcohol + Oxygen ⟶ Carbon Dioxide + Water

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3
Q

Under what conditions does combustion occur?

A

high temperature

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4
Q

Is combustion exothermic or endothermic?

A

exothermic

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5
Q

Under what condition do alcohols become oxidised?

A

acidified potassium dichromate solution

K2Cr2O7 (aq) + H2SO4 (aq)

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6
Q

What is the oxidising agent in oxidation of alcohols/aldehydes?

A

acidified potassium dichromate ions

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7
Q

During oxidation, are potassium dichromate ions oxidised or reduced?

A

reduced

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8
Q

What is the colour change during oxidation of alcohols and the formation of what ion is responsible for this colour change?

A

orange to green

Cr3+

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9
Q

What is the general equation for oxidation of PRIMARY ALCOHOLS?

A

PARTIAL: Primary alcohol + [O] ⟶ Aldehyde + Water

COMPLETE: Primary alcohol + 2[O] ⟶ Carboxylic acid + Water

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10
Q

What organic product is formed when a PRIMARY alcohol undergoes oxidation under GENTLE HEATING + EXCESS ALCOHOL?

A

aldehyde

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11
Q

What organic product is formed when a PRIMARY alcohol undergoes oxidation under REFLUX + EXCESS OXIDISING AGENT?

A

carboxylic acid

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12
Q

What conditions are used in PARTIAL OXIDATION of PRIMARY alcohols?

A

GENTLE HEATING

EXCESS ALCOHOL - less complete oxidation
(∵ not enough oxidising agent to fully oxidise)

ALDEHYDE DISTILLED OUT - prevents further oxidation into carboxylic acid

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13
Q

What conditions are used in COMPLETE OXIDATION of PRIMARY alcohols?

A

REFLUX

EXCESS OXIDISING AGENT - make sure all alcohol molecules fully oxidised

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14
Q

What organic product is formed when a SECONDARY alcohol undergoes oxidation?

A

ketone

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15
Q

What conditions are used in the oxidation of SECONDARY alcohols?

A

reflux - ensure reaction is complete

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16
Q

What organic product is formed when a TERTIARY alcohol undergoes oxidation?

A

TERTIARY ALCOHOLS CANNOT UNDERGO OXIDATION REACTIONS

17
Q

Under reflux:

Primary alcohols oxidise to _____.

Secondary alcohols oxidise to _____.

A

carboxylic acids

ketones

18
Q

What compound can be used as a test for the presence of a carboxylic acid?

A

METAL CARBONATE

CO2 gas released since acid + metal carbonate ⟶ salt + water + carbon dioxide

19
Q

(Carboxylic) acid + metal carbonate ⟶

A

salt + water + carbon dioxide

20
Q

oxidising a primary alcohol ⟶ aldehyde,

what is the change in number of hydrogens and oxygens?

A

loses 2 hydrogens (oxygen added takes these 2 hydrogens to form water)

Overall no change in oxygen.

21
Q

the [O] oxygen being added to alcohols causes the formation of what inorganic molecule?

(except aldehyde -> carboxylic acid)

A

water

O takes 2 hydrogens from the alcohol molecule.

22
Q

What is the general equation for dehydration of an alcohol?

A

Alcohol ⟶ Alkene + Water

23
Q

What are the conditions for dehydration of an alcohol?

A

PHOSPHORIC ACID catalyst, H3PO4

REFLUX

24
Q

What is a dehydration reaction?

A

2 hydrogens + 1 oxygen removed from saturated molecule

forming unsaturated molecule + water

25
Q

What is a substitution reaction?

A

reaction where

atom/groups of atoms are REPLACED

by atom/group of atoms.

26
Q

How many [O] must be added to a primary alcohol to oxidise it to an aldehyde?

A

1

27
Q

How many [O] must be added to a primary alcohol to oxidise it to a carboxylic acid?

A

2

28
Q

How many [O] must be added to a secondary alcohol to oxidise it to a ketone?

A

1

29
Q

Which oxidation reaction involves this:

[O] added to alcohol takes 2 hydrogens from the alcohol, forming water.

A

primary alcohol ⟶ aldehyde

or

secondary alcohol ⟶ ketone

30
Q

Which oxidation reaction involves this:

[O] added is incorporated into the molecule by addition.

A

Aldehyde ⟶ carboxylic acid

A level Chemistry OCR A (44 decks)

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