alcohols

Question 1

what is a carbonyl group

Answer 1

C=O

Question 2

give the description, formula and nomenclature of an aldehyde

Answer 2

Carbonyl bonded to at least one H atom
CHO
…al

Question 3

how do you name an aldehyde

Answer 3

Rootanal
carbonyl group in aldehyde is always C1 so number not needed

Question 4

give the description, formula and nomenclature of a ketone

Answer 4

Carbonyl bonded to two C atoms
CO
…one

Question 5

give the description, formula and nomenclature of a carboxylic acid

Answer 5

Carbonyl bonded to an OH group
COOH
…oic acid

Question 6

give the conditions for fermentation

Answer 6

Yeast catalyst

Limited supply of O2

Temperature of 30-40 °C

Question 7

Explain why neither a low temperature nor a high temperature is suitable for fermentation

Answer 7

· Temperature too low: reaction too slow

· Temperature too high: destroys or denatures yeast enzyme

Question 8

what does carbon-neutral mean

Answer 8

overall there is no CO2 released into the atmosphere when using bio-ethanol as a fuel

Question 9

give the equations for ethanol produced from fermentation

Answer 9

1. Photosynthesis: 6CO2 + 6H2O → C6H12O6 + 6O2
2. Fermentation: C6H12O6 → 2CH3CH2OH + 2CO2
3. Combustion: 2CH3CH2OH + 6O2 → 4CO2 + 6H2O

Question 10

give reasons that bio-ethanol is not really a carbon-neutral fuel

Answer 10

harvesting and transportation will involve burning/ combustion of fossil fuels producing CO2

Question 11

give advantages and disadvantages of fermentation

Answer 11

Advantages
Glucose is renewable source
Lower temperatures require less energy
Simpler equipment required is cheaper

Disadvanatages

Land used to grow crops is not available for food crops
Ethanol is impure and must be distilled to purify
Low yield
Rate is slow
Batch production method is difficult to automate

Question 12

give advantages and disadvantages of direct hydration

Answer 12

Advantages
High-purity ethanol produced
Continuous production
Fast rate of reaction

Disadvantages
Crude oil is not renewable
High temperature and pressure requires a lot of energy (expensive)
Hi-tech equipment required (expensive)

Question 13

give the reaction mechanism and conditions to form alkenes from alcohols

Answer 13

· Reaction: Dehydration

· Mechanism: Elimination

· Conditions: Hot conc. H2SO4 (catalyst)

Question 14

why is separating funnel used

Answer 14

A separating funnel can be used to remove the impurities.

Question 15

Stages of Separation

Answer 15

1. add impure organic liquid and add a small portion of sodium hydrogen carbonate solution.
2. Stopper the separating funnel and shake.
3. Periodically invert the funnel and open the tap to release any pressure that will have built up.
4. Allow the separating funnel to stand and the layers to separate.
5. Remove the stopper and run off the bottom aqueous layer into a conical flask – discard
6. Run off the organic layer into a clean conical flask and add a spatula of drying agent (anhydrous calcium chloride or anhydrous magnesium sulfate)
7. Swirl the flask until the liquid turns from cloudy to clear
8. Decant the liquid into another flask in preparation for it to be re-distilled

Question 16

how do you name a ketone

Answer 16

rootan-#-one
can be at different positions so requires a number

Question 17

give the equation for the reaction that occurs when hydrogen carbonate solution is added in a separating funnel

Answer 17

2H+ + CO3 2- → H2O + CO2

Question 18

Why is sodium hydrogen carbonate solution added to the impure product in the separating funnel

Answer 18

The sodium hydrogen carbonate solution will react with the acid catalyst not used up in the reaction thus neutralising it.

Question 19

Describe how re-distillation removes unreacted cyclohexanol from the product

Answer 19

Cyclohexanol and cyclohexene have different boiling points

Cyclohexene has weak induced dipole-dipole attractions between moleceules

Cyclohexanol has stronger Hydrogen bonds between its molecules

Cyclohexene has a lower boiling point and will boil first in the mixture, and thus be collected as a distillate when separated from the cyclohexanol.

Question 20

what is the test for presence/oxidation of primary or secondary alcohol

Answer 20

add acidified potassium dichromate (H+/Kr2Cr2O7)
orange to green

Question 21

give the reagents conditions and products for the oxidation of a primary alcohol to aldehyde

Answer 21

Reagent: Acidified K2Cr2O7 Conditions: distillation
1 [O] added
1 water produced

Question 22

give the reagents conditions for the oxidation of an aldehyde to carboxylic acid

Answer 22

Reagent: Acidified K2Cr2O7 Conditions: reflux
1 [O] is added
no water produced (bc no hydrogens lost)

Question 23

give the reagents conditions and 1 extra product for the oxidation of a primary alcohol to carboxylic acid

Answer 23

Reagent: Acidified K2Cr2O7 Conditions: Heat under reflux, excess oxidising agent
2 [O] used
1 water produced

Question 24

give the reagents conditions and 1 extra product for the oxidation of a secondary alcohol to ketones

Answer 24

Reagent: Acidified K2Cr2O7 Conditions: distillation
1 [O] used
1 water produced

Question 25

give 2 features of a condenser

Answer 25

- long glass tube with a water jacket - water goes in from bottom and out from top

Question 26

give the purpose of a condenser

Answer 26

Cools hot vapour and condenses it to liquid

Question 27

why are anti bumping granules added to the reaction mixture

Answer 27

Prevent the formation of large bubbles

Question 28

Why is reflux used to oxidise a primary alcohol to a carboxylic acid?

Answer 28

so that aldehyde remains in the reaction to be oxidised to a carboxylic acid

Question 29

ethanol → ethanal → ethanoic acid Describe what happens when a reaction mixture is refluxed and why it is necessary, for complete oxidation to a carboxylic acid

Answer 29

ethanol is oxidised to ethanal which has a small boiling point so evaporates out the flask into the condenser where it is cooled and condenses back into a liquid it drips back into the flask to be oxidised to the carboxylic acid

Question 30

What happens to the aldehyde as it is produced during distillation?

Answer 30

The aldehyde forms as a vapour and escapes from the reaction mixture into the condenser

Question 31

Why is distillation used when producing an aldehyde from a primary alcohol?

Answer 31

Distillation allows the aldehyde to escape the reaction mixture and prevents further oxidation

Question 32

give 2 reagents to test for aldehydes and give their observations for when aldehyde is and isnt present

Answer 32

· Reagent used to test for aldehydes: Tollen’s reagent · Observation when aldehyde present: Silver mirror forms · Observation when aldehyde not present: No visible change · Reagent used to test for aldehydes: Fehling’s solution · Observation when aldehyde present: brick-red precipitate · Observation when aldehyde not present: No visible change

Question 33

state the reagents and observations for when testing for carboxylic acids

Answer 33

· Reagent used to test for carboxylic acids: Na2CO3 · Observation when carboxylic acid present: effervescence · Observation when carboxylic acid not present: No visible change