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chem > alcohols > Flashcards

alcohols Flashcards

1
Q

what is a carbonyl group

A

C=O

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2
Q

give the description, formula and nomenclature of an aldehyde

A

Carbonyl bonded to at least one H atom
CHO
…al

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3
Q

how do you name an aldehyde

A

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

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4
Q

give the description, formula and nomenclature of a ketone

A

Carbonyl bonded to two C atoms
CO
…one

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5
Q

give the description, formula and nomenclature of a carboxylic acid

A

Carbonyl bonded to an OH group
COOH
…oic acid

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6
Q

give the conditions for fermentation

A

Yeast catalyst

Limited supply of O2

Temperature of 30-40 °C

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7
Q

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

A

· Temperature too low: reaction too slow

· Temperature too high: destroys or denatures yeast enzyme

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8
Q

what does carbon-neutral mean

A

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

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9
Q

give the equations for ethanol produced from fermentation

A
  1. Photosynthesis: 6CO2 + 6H2O → C6H12O6 + 6O2
  2. Fermentation: C6H12O6 → 2CH3CH2OH + 2CO2
  3. Combustion: 2CH3CH2OH + 6O2 → 4CO2 + 6H2O
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10
Q

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

A

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

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11
Q

give advantages and disadvantages of fermentation

A

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

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12
Q

give advantages and disadvantages of direct hydration

A

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)

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13
Q

give the reaction mechanism and conditions to form alkenes from alcohols

A

· Reaction: Dehydration

· Mechanism: Elimination

· Conditions: Hot conc. H2SO4 (catalyst)

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14
Q

why is separating funnel used

A

A separating funnel can be used to remove the impurities.

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15
Q

Stages of Separation

A
  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
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16
Q

how do you name a ketone

A

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

17
Q

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

A

2H+ + CO3 2- → H2O + CO2

18
Q

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

A

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

19
Q

Describe how re-distillation removes unreacted cyclohexanol from the product

A

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.

20
Q

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

A

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

21
Q

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

A

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

22
Q

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

A

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

23
Q

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

A

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

24
Q

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

A

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

25
Q

give 2 features of a condenser

A
  • long glass tube with a water jacket
  • water goes in from bottom and out from top
26
Q

give the purpose of a condenser

A

Cools hot vapour and condenses it to liquid

27
Q

why are anti bumping granules added to the reaction mixture

A

Prevent the formation of large bubbles

28
Q

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

A

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

29
Q

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

A

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

30
Q

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

A

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

31
Q

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

A

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

32
Q

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

A

· 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

33
Q

state the reagents and observations for when testing for carboxylic acids

A

· Reagent used to test for carboxylic acids: Na2CO3

· Observation when carboxylic acid present: effervescence

· Observation when carboxylic acid not present: No visible change

chem (9 decks)

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