ALDEHYDES + KETONES

Question 1

where to aldehydes have their carbonyl group? (1)

Answer 1

aldehydes have their carbonyl group at the end of the carbon chain .

Question 2

what is the carbonyl group? (1)

Answer 2

c=o

Question 3

what is the suffix for an aldehyde? (1)

Answer 3

-al

Question 4

where is the carbonyl group in ketones? (1)

Answer 4

ketones have their carbonyl group in the middle of the carbon chain.

Question 5

what is the suffix for a ketone? (1)

Answer 5

their names finish with -one

Question 6

what is the difference between aldehydes and ketones in terms of oxidising agents? (1)

Answer 6

oxidising agents will react with aldehydes to produce carboxylic acids, but not ketones.

Question 7

how can we test for the presence of a aldehyde or ketone? (1)

Answer 7

using tollens reagent which is a colourless solution of silver nitrate dissolved in a aqueous ammonia.

Question 8

what occurs during the tollens reagent test? (2)
ALDEHYDE

Answer 8

when heated in a test tube with an aldehyde the Ag+ ions in tollens reagent are reduced to Ag atoms and a silver mirror forms in a few minutes.

Question 9

What occurs during the tollens reagent test? (1)
KETONE

Answer 9

Ketones cant be oxidised by tollens reagent, so with ketones there is no reaction and no colour change.

Question 10

what occurs during the Fehling’s solution test? (2)
ALDEHYDE

Answer 10

If its heated with an aldehyde the copper (ii) ions are reduced to a brick-red precipitate pf copper (I) oxide.

Question 11

what occurs during the Fehling’s solution test? (1)
KETONE

Answer 11

As with tollens reagent, ketones don’t react with Fehling’s solution, so no precipitate formed.

Question 12

what alcohol can make aldehydes? (1)

Answer 12

primary alcohols can be oxidised to produce aldehydes and carboxylic acids

Question 13

what alcohol can make ketones? (1)

Answer 13

secondary alcohols can be oxidised to make ketones

Question 14

what reducing agent is usually used to reduced oxidation of alcohols? (1)

Answer 14

sodium tetrahydridoborate (III) or sodium borohydride dissolved in water with methanol

Question 15

what mechanism reaction occurs to aldehydes and ketones? (1)

Answer 15

nucleophilic addition reactions

Question 16

what occurs in this nucleophilic addition reaction? (1)

Answer 16

potassium cynaide will react with carbonyls to produce hydroxynitriles.

Question 17

what is a nucleophile? (1)

Answer 17

a nucleophile attacks the molecule and adds itself as an extra group.

Question 18

what happens to the potassium cyanide in this nucleophilic addition reaction? (1)

Answer 18

potassium cyanide dissociates in water to form K+ ions and CN- ions

Question 19

what does the CN- group do in the nucleophilic addition reaction? (1)

Answer 19

the CN- group attacks thee partially positive carbon atom and donates a pair of electrons. both electrons from the double bond transfer to the oxygen.

Question 20

what happens to the H+ ions in the nucleophilic addition reaction? (1)

Answer 20

H+ ions add to the oxygen to form the hydroxyl group (OH), acidified KCN is usually used so there’s a source of H+ ions

Question 21

what are the chemical concerns with potassium cyanide? (1)

Answer 21

potassium cyanide is an irritant and is also extremely dangerous is its ingested or inhaled. It can also react with oxygen to produce hydrogen cyanide a toxic gas.