3.5 Alcohols

Question 1

What is the functional group of an alcohol?

Answer 1

Hydroxyl group -OH

Question 2

What is the general formula of an alcohol?

Answer 2

Cn H2n+1 OH

Question 3

How do you name alcohols?

Answer 3

Hydroxyl- or -OH

Question 4

What kind of intermolecular forces do alcohols have? why?

Answer 4

Hydrogen boning, due to the electronegative difference in the OH bond

Question 5

How do alcohols melting point and boiling points compare to other hydrocarbons of similar C chain lengths? Why?

Answer 5

Higher, because they have hydrogen bonding —> stronger than van der Waals forces

Question 6

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

Answer 6

Soluble when short chain- OH hydrogen bonds hydrogen bond in water

Insoluble when long chain- non-polarity of C-H bond takes precedence

Question 7

What make an alcohol primary?

Answer 7

C bonded to OH is only bonded to one other C atom

Question 8

What makes an alcohol secondary?

Answer 8

C bonded to OH is bonded to two other C atoms

Question 9

What makes an alcohol tertiary?

Answer 9

C bonded to OH is bonded to three other C atoms

Question 10

How can ethanol be made from crude oil?

Answer 10

Hydration of ethene via electrophilic addition (phosphoric acid catalyst H3PO4)

Question 11

What are the advantages and disadvantages of making ethanol from crude oil?

Answer 11

Advantages- fast, continuous process, ethanol, has a high purity

Disadvantages- not renewable as from crude oil

Question 12

How can ethanol be made by fermentation?

Answer 12

Plant carbo hydrates broken down and fermented by enzymes in yeast —> ethanol

Question 13

What conditions are needed for ethanol to be formed by fermentation?

Answer 13

Enzymes in yeast as catalyst, 35 degrees C, anaerobic conditions

Question 14

Write an equation for the reaction which takes place when ethanol is being formed by fermentation

Answer 14

Question 15

What are the advantages and disadvantages of making ethanol by fermentation?

Answer 15

Advantages- renewable as from plants

Disadvantages- slow, batch process, enzymes stop working at 15% alcohol so the solution is not pure, needs to be fractionally distilled

Question 16

In the future, how might most ethene be made? Why is it not made like this at the moment?

Answer 16

Dehydrate ethanol made by fermentation- ethene

Not economical at the moment

Question 17

Define carbon neutral

Answer 17

No net addition of CO2 to the atmosphere- carbon dioxide released when combusted= carbon dioxide absorbed as a plant

Question 18

Explain how using ethanol in petrol engines could be considered to be carbon neutral

Answer 18

Carbon dioxide released in fermentation and combustion= carbon dioxide absorbed when growing

Question 19

Why would it probably not be entirely carbon neutral to use ethanol?

Answer 19

Other “carbon costs” associated with it e.g. transport

Question 20

What is a commercial fuel that uses ethanol? What else does it contain and why?

Answer 20

Methylated spirits- methanol? (toxic, so it can’t be drunk)

Question 21

Write an equation for the combustion of ethanol?

Answer 21

Question 22

What is an elimination reaction?

Answer 22

The removal of a smaller molecule from a larger one

Question 23

Which group leaves the parent molecule in the case of alcohols?

Answer 23

OH and a H (to form water)

Question 24

What physical conditions are needed for the elimination reaction from alcohols to alkenes? (2 alternatives)

Answer 24

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

Question 25

Draw a mechanism for the dehydration of ethanol

Answer 25

Question 26

Draw a method for dehydration of ethanol in the lab

Answer 26

Question 27

What forms if you partially oxidise a primary alcohol

Answer 27

An aldehyde

Question 28

What conditions are needed to partially oxidise a primary alcohol?

Answer 28

Dilute sulphuric acid, potassium dichromate (VI), distill product as it's produced, gentle heating

Question 29

Write an equation for the partial oxidation of ethanol

Answer 29

Question 30

What forms if you fully oxidise a primary alcohol?

Answer 30

A carboxylic acid

Question 31

What conditions are needed for a primary alcohol to be fully oxidised?

Answer 31

Concentrated sulphuric acid, potassium, dichromate (VI), reflux for about 20 mins, strong heating

Question 32

Write an equation for the full oxidation of ethanol

Answer 32

Question 33

What forms if you oxidise a secondary alcohol?

Answer 33

A ketone

Question 34

Why can it not be oxidised further and why can't a tertiary alcohol be oxidised?

Answer 34

A carbon-carbon bond would have to break

Question 35

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

Answer 35

Concentrated sulphuric acid, potassium dichromate (VI), reflux for about 20 mins, strong heating

Question 39

How do you name aldehydes?

Answer 39

Suffix - al e.g ethanal

Question 40

Write an equation for the oxidation of propane-2-ol.

Answer 40

Question 40

What is an aldehyde? What is its functional group

Answer 40

Molecule with C=O group at the end of a carbon chain, carbonyl functional group (C=0)

Question 41

What is a ketone? What is its functional group?

Answer 41

Molecule with C=O group in the middle of a carbon chain, carbonyl functional group (C=O)

Question 42

How do you name ketones?

Answer 42

Suffix -one e.g propanone

Question 43

What is a carboxylic acid? What is its functional group?

Answer 43

Molecule with COOH group, which has to be at the end of a carbon chain. Carboxyl functional group (made up of carbonyl C=O and hydoxyl OH- group)

Question 45

What does the Tollens' test give a positive result for?

Answer 45

Aldehydes

Question 45

What is in Tollens reagent? How does this react with the substance to be tested?

Answer 45

Silver nitrate in NH3 (aq)- oxidises aldehydes but not ketones Complex silver (I) ions reduced to Ag(s)

Question 46

How do you carry out the Tollens' test?

Answer 46

Add equal volumes of substance being tested and Tollens' reagent to a test tube, leave in water bath for 10 mins and observe any changes

Question 47

What is the result of the Tollens' test for aldehydes and ketone?

Answer 47

Aldehydes- silver mirror forms Ketones- no visible change

Question 48

What does Fehling's solution give a positive test result for?

Answer 48

aldehydes

Question 49

What is in Fehling's? How does this react with the substance to be tested?

Answer 49

Blue copper (II) complex ions - gentle oxidising agent Reduced to CU+ ions (brick red)

Question 50

What condition do you need to use the Fehling's solution?

Answer 50

Heat

Question 51

What result do aldehydes and ketone five in the Fehling's test?

Answer 51

Aldehydes- brick red ppt Ketones- no visible change