organic chem; alcohols

Question 1

Alcohols have the functional group…

Answer 1

…OH (hydroxyl)

Question 2

Primary alcohols have…

Answer 2

…1 alkyl group attached to the C with OH

Question 3

Secondary alcohols have…

Answer 3

…2 alkyl group attached to the C with OH

Question 4

Tertiary alcohols have…

Answer 4

……1 alkyl group attached to the C with OH

Question 5

How are alkenes formed from alcohols?

Answer 5

By eliminating water from the alcohol (dehydration)

Question 6

What is a sustainable way of producing alkenes from alcohols?

Answer 6

By using alcohol made from fermentation of plants

Question 7

Use of alkenes

Answer 7

To make polymers which can be used to make plastics

Question 8

Dehydration involves the use of…

Answer 8

…acid catalyst (sulfuric or phosphoric acid)

Question 9

General equation of dehydration

Answer 9

Ethanol → ethene + water

Question 10

Dehydration of alcohols shown using…

Answer 10

…elimination mechanism

Question 11

Dehydration of non-primary alcohols forms…

Answer 11

…2 different alkenes

Question 12

Dehydration of alcohols is conducted through…

Answer 12

…distillation

Question 13

Why is distillation used?

Answer 13

To separate useful alkenes from impurities such as alcohols, water & acid

Question 14

How does distillation work?

Answer 14

Separates chemical by boiling point

Question 15

How is cyclohexane formed?

Answer 15

Formed by cyclohexanol using distillation, separation & purification techniques

Question 16

Process of forming cyclohexane (step 1)

Answer 16

• add conc sulfuric, phosphoric & cyclohexanol into a round bottomed flask
• add several anti-bumping granules to allow smooth boiling process
• use a heating mantle to warm the reactants up to 83˚ (b.p of cyclohexanol)
• bunsen burner is NOT used as its flammable
• chemicals with b.p less than 83˚ will evaporate, enter condenser & cool down back to liquid
• product collected in a vessel
• the product will still have small amounts of impurities such as un reacted cyclohexanol & water

Question 17

Process of forming cyclohexane (step 2)

Answer 17

• add products from step 1 into separating funnel
• add water to dissolve soluble impurities — creates aqueous solution
• 2 layers form — top layer is impure cyclohexane, bottom layer is water soluble impurities

Question 18

Process of forming cyclohexane (step 3)

Answer 18

• take the impure cyclohexane from step 2 & add to round bottomed flask
• add anhydrous calcium chloride — removes remaining aqueous substances
• invert flask & leave for 20-30 mins

Question 19

Hydration of alkenes…

Answer 19

…produces alcohols

Question 20

How is alcohol formed using alkenes?

Answer 20

Steam & acid catalyst to create alcohol

Question 21

How is ethanol made?

Answer 21

• by reacting steam & ethene with phosphoric acid
• temp 300˚ and 60 atms

Question 22

Fermentation is…

Answer 22

…alternative to ethene & steam when making ethanol

Question 23

Why is fermentation used instead of using ethanol?

Answer 23

• ethanol requires crude oil which is not renewable
• fermentation uses renewable source of glucose from plants

Question 24

Process of fermentation

Answer 24

• uses yeast in anaerobic conditions — exo reaction
• yeast is enzyme which converts glucose into CO2 & ethanol
• fractional distillation used to obtain pure alcohol

Question 25

Advantage of using fermentation

Answer 25

Requires little equipment & uses renewable resources — cheap process

Question 26

Disadvantage of using fermentation

Answer 26

Fractional distillation requires energy & time — expensive

Question 27

Biofuel such as … are made from dead … …

Answer 27

…ethanol …biological matter

Question 28

Advantages of biofuels

Answer 28

- are renewable — more sustainable than crude oil - produce CO2 but are classes as carbon neutral so sugar cane absorbs it

Question 29

Disadvantage of biofuels

Answer 29

- expensive to convert existing petrol engines to take fuels with higher conc of ethanol - land that could be used to grow foods are being used to make fuel — can cause food shortages

Question 30

Alcohols can be oxidises to …

Answer 30

…aldehydes, ketones & carboxylic acids

Question 31

Alcohols are oxidised using…

Answer 31

…potassium dichromate (K2Cr2O7) — turns from orange to green

Question 32

Primary alcohols are oxidised to…

Answer 32

…aldehydes then carboxylic acids

Question 33

Secondary alcohols can be oxidise to…

Answer 33

…ketones

Question 34

Tertiary alcohols are oxidised to…

Answer 34

…cannot be oxidised using dichromate

Question 35

What techniques are used in the oxidation of alcohols?

Answer 35

Distillation & reflux

Question 36

How is carboxylic acid extracted from alcohol?

Answer 36

- distillation is used to remove aldehyde as they have a lower b.p than alcohol - reflux & excess oxidising agent used to make carboxylic acid

Question 37

How are ketones extracted from alcohols?

Answer 37

- reflux & oxidising agent used to make ketone - secondary alcohols oxidise when potassium dichromate is added

Question 38

What is used to distinguish between aldehydes & ketones?

Answer 38

Fehling’s solution & Tollens reagent

Question 39

Fehling’s solution

Answer 39

- blue as it contains Cu2+ ions - add warm to aldehydes - solution goes from blue to break red precipitate — +be test aldehydes - remains blue for ketones

Question 40

Tollen’s reagent

Answer 40

- added warm - aldehydes: tollens reduced to silver - ketones: no silver precipitate formed