aldehydes and carboxylic derivatives

Question 1

Tollens why cant we heat w bunsen burner

Answer 1

when adding aldehyde or ketones to supply reac w eneryg heat using a water bath. no bunsen burner as aldehydes and ketones are flammable

Question 2

reduction of aldehydes and ketones

Answer 2

aldehydes make primary alcohols (2h) ketones make secondary alcohols

Question 3

what is this and potassium cyanide and carbonyl groups an example of

Answer 3

nucleophillic addition

Question 4

what can happen if we use an unsymmetrical ketone or aldehyde

Answer 4

we can make a mixture of enantiomers

Question 5

using kcn

Answer 5

irritant dangerous if ingested or inhaled, when it reacts w moisture it can form toxic gases eg hcn. to reduce wear gloves safety goggles lab coat to prevent contamination and use a fume cupboard

Question 6

In order to ensure that the oxidation to ethanoic acid is complete, the reaction is
carried out under reflux.
Describe what happens when a reaction mixture is refluxed and why it is necessary,
in this case, for complete oxidation to ethanoic acid.

Answer 6

A mixture of liquids is heated to boiling point for a prolonged time
Vapour is formed which escapes from the liquid mixture, is changed back into
liquid and returned to the liquid mixture
Any ethanal and ethanol that initially evaporates can then be oxidised

Question 7

esterification conditions

Answer 7

sulfuric acid catalyst

Question 8

acid hydrolysis vs base hydrolysis

Answer 8

acid with water and h+ catalyst. splits into a carboxylic acid and an alcohol using h2s04 or hcl under reflux. however w a base. reacts w oh- to make a carboxylate ion and an alcohol.

Question 9

phenyl propanoate+ naoh

Answer 9

ch3ch2coo-na+ and phenyl

Question 10

vegetable oils vs animal fats

Answer 10

unsaturated hydrocarbon chains that are not straight which means the chains cant pack together closely and so have low vdw forces and so lower mp and so liquid room temp. animal fat opposite saturated uniform pack together strong vdws, solids at rtp

Question 11

carboxylic acids + carbonates- what does this reac produce

Answer 11

carboxyolate salt, water, co2

Question 12

equilibrium

Answer 12

carboxylic acids are weak acids therefore they disasociate poorly so they partially ionise so equilibirum lies well over to the left so not much carboxylate ions and h+’s are formed.

Question 13

ch3cooh+ na2co3 and nahco3 equations

Answer 13

2ch3cooh+na2co3–>2ch3coona+h2o+co2

ch3cooh+nahco3—>ch3coona+h20+co2

Question 14

base hydrolysis vs acid hydrolysis. using an ester.

Answer 14

ethyl ethanoate+h20(h+ catalyst eg h2so4)–>–carboxylate ion+alcohol.
so the acid hydrolysis one has a lower yield of the cooh and alcohol since the reac is reversible but the base one is one way so higher yield. but the base one produces a carboxylate ion rather than the cooh so its more expensive to make a cooh but u could further react it

Question 15

further reac to ensure base hydrolysis forms a cooh

Answer 15

salt eg ch3coo-na+ +hcl–>ch3cooh+ nacl

Question 16

conditions for esterification

Answer 16

coohs can react w alcohols in the prescence of a strong acid catalyst to form esters. carried out under reflux.

Question 17

why are acid anhydrides used rather than acyl chlorides

Answer 17

cheaper and safer to use, less corrosive and doesnt produce toxic hcl gas.however it is a slower reaction the reaction with acyl chlorides is faster.

Question 18

Give one advantage of the use of propanoyl chloride instead of propanoic acid in the laboratory preparation of methyl propanoate from methanol.

Answer 18

faster reaction and also its not a reversible reac and so has a bigger yield.

Question 19

The student purified the crude solid product, N−phenylethanamide, by
recrystallisation.
(i) Outline the method that the student should use for this recrystallisation

Answer 19

Dissolve the product in the minimum volume of water / solvent (in a
boiling tube / beaker)
If dissolving is not mentioned, CE = 0 / 4
Hot water / solvent
Steps must be in a logical order to score all 4 marks
Allow the solution to cool and allow crystals to form.
Filter off the pure product under reduced pressure

Question 20

) Assume that the reaction goes to completion.
Suggest two practical reasons why the percentage yield for this reaction may
not be 100%

Answer 20

) Any two from:
Product left in the beaker or glassware
Sample was still wet
Sample lost during recrystallisation

Question 21

The product of step 1 was purified by recrystallisation as follows.
The crude product was dissolved in the minimum quantity of hot water and the
hot solution was filtered through a hot filter funnel into a conical flask. This filtration
removed any insoluble impurities. The flask was left to cool to room temperature.
The crystals formed were filtered off using a Buchner funnel and a clean cork was
used to compress the crystals in the funnel. A little cold water was then
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poured through the crystals.
After a few minutes, the crystals were removed from the funnel and weighed.
A small sample was then used to find the melting point.
Give reasons for each of the following practical steps.
The minimum quantity of hot water was used
……………………………………………………………………….

Answer 21

The minimum quantity of hot water was used:
To ensure the hot solution would be saturated / crystals would form on cooling

The flask was left to cool before crystals were filtered off:
Yield lower if warm / solubility higher if warm

The crystals were compressed in the funnel:
Air passes through the sample not just round it

A little cold water was poured through the crystals:
To wash away soluble impurities

Question 22

The melting point of the sample in part (b) was found to be slightly lower than a
data-book value.
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Suggest the most likely impurity to have caused this low value and an improvement
to the method so that a more accurate value for the melting point would be obtained.

Answer 22

Water

Press the sample of crystals between filter papers

Question 23

When T is heated with an excess of methanol, glycerol is formed together with a
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mixture of methyl esters.
(i) Give a use for this mixture of methyl esters.

Answer 23

biodiesel

Question 24

Describe the experimental conditions and the practical method used to ensure
that the acid is obtained in a high yield. Draw a diagram of the assembled
apparatus you would use.
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Conditions …………………………………………………………………………………
…………………………………………………………………………………………………
Apparatus

Answer 24

Excess acidified potassium dichromate(VI)
Reflux (for some time)
In the diagram credit should be given for
• a vertical condenser
• an apparatus which would clearly work

Question 25

) Describe the different experimental conditions necessary to produce propanal
in high yield rather than propanoic acid.

Answer 25

Distillation

Immediately (the reagents are mixed)

Question 26

Propan-1-ol is a volatile, flammable liquid.
Give one safety precaution that should be used during the reaction to minimise this
hazard.

Answer 26

keep away from naked flames

Question 27

You are provided with a small sample of pure aspirin in a melting point tube.
Describe briefly how you would determine an accurate value for the melting point of
aspirin.

Answer 27

Heat melting point tube in an oil bath

slowly near the melting point

Question 28

Q6.Aldehydes can be prepared from acyl chlorides.
State how an aldehyde could be tested to show whether it is contaminated with traces of
unreacted acyl chloride.
State what you would observe

Answer 28

silver nitrate (solution) white precipitate

Question 29

Explain the purpose of each underlined point.
Minimum volume ………………………………………………………………………………………..
…………………………………………………………………………………………………………………
Hot water ………………………………………………………………………………………………….
…………………………………………………………………………………………………………………
Filtered hot ………………………………………………………………………………………………..
…………………………………………………………………………………………………………………
Cooled in ice ……………………………………………………………………………………………..
…………………………………………………………………………………………………………………
Washed with cold water ……

Answer 29

Minimum volume and hot water:

to obtain saturated solution
to increase yield / reduce amount left in solution
enable crystallisation (on cooling)

Filtered hot: to remove insoluble impurities / to prevent crystals forming during
filtration

Cooled in ice: to increase amount of crystals that are formed

1
Washed with cold water: to remove soluble impurities

Question 30

Haloalkanes such as CH3Cl are used in organic synthesis.
Outline a three-step synthesis of CH3CH2NH2 starting from methane. Your first step
should involve the formation of CH3Cl
In your answer, identify the product of the second step and give the reagents and
conditions for each step

Answer 30

CH3CN or ethan(e)nitrile or ethanonitrile
not ethanitrile
but allow correct formula with ethanitrile
1
for each step wrong or no reagent loses condition mark
contradiction loses mark
1
Step 1 Cl2
uv or above 300 °C
wrong or no reagent loses condition mark
1
Step 2 KCN
1
aq and alcoholic (both needed)
allow uv light/(sun)light/uv radiation
1
Step 3 H2/Ni or LiAlH4 or Na/C2H5OH
not CN–
 but mark on
NOT HCN or KCN + acid, and this loses condition mark
NOT NaBH4
Sn/HCl (forms aldehyde!)
ignore conditions

Question 31

Although Terylene is biodegradeable, it is preferable to recycle objects made from
Terylene.
Give one advantage and one disadvantage of recycling objects made from
Terylene.

Answer 31

Adv reduces landfill
saves raw materials
lower cost for recycling than making from scratch
reduces CO2 emissions by not being incinerated
not allow cost without qualification
ignore energy uses
1
Disad difficulty/cost of collecting/sorting/processing
product not suitable for original purpose, easily contaminated

Question 32

use of esters

Answer 32

perfumes and food flavourings
solvents as polar can form hydrogen bonds w water
low bp can make glue
plasticisers

Question 33

why are vegetable oils liquids at room temp

Answer 33

they have unsaturated hydrocarbon chains that are not straight which means the chains cannot pack closely together, so they have lower van der waals forces hence, lower melting points so their liquids at room temp

Question 34

why are animal fats solids at room temp

Answer 34

they have saturated hydrocarbon chains that are straight and more uniform than oils which means that the chains can pack together closely and hence have much higher vdw forces so they have higher melting points and are solids at room temp

Question 35

explain how carbon dioxide causes global warming

Answer 35

c=o bonds in co2 absorb infrared radiation

this does not escape

Question 36

equation to show the role of aluminium chloride as a catalyst

Answer 36

AlCl4+ H+ –> Al3Cl +HCl

Question 37

how would you draw a diagram to show how to filter crude oil under reduced pressure

Answer 37

side arm flask with flat bottomed funnel w filter paper clearly shown

Question 38

you are provided with a small sample of pure aspirin in a melting point tube describe briefly how you wuold determine an accurate value for the mp

Answer 38

heat the melting point tube in an oil bath, slowly near the melting point.

Question 39

suggest why excess naoh is used
suggest why an electric heater is used rather than a bunsen burner
suggest why reflux is used in this hydrolysis
suggest why sodium benzoate is soluble in cold water but benzoic acid is insoluble in cold water

Answer 39

to ensure that all the ester reacts
as the ethanol is flammable
reflux allows reactant vapours to be returned to the reaction mixture
sodium benzoate is soluble as it is ionic, benzoic acid is insoluble as despite the polarity of the cooh the benzene ring is non polar

Question 40

describe the method the studebt should use to purify benzoic acid

Answer 40

dissolve crude product in hot water of minimum volume
filter to remove insoluble impurities
cool to recrystallise
filter under reduced pressure
wash with cold water and dry