aldehydes and ketones

Question 1

functional group and naming of aldehydes

Answer 1

CHO functional group ending, ending in -al e.g. ethanal

Question 2

functional group and naming of ketones

Answer 2

CO functional group in the middles, ending in -one, e.g. propanone

Question 3

oxidation of aldehydes

Answer 3

aldehydes are readily oxidised into carboxylic acids due to acidified potassium dichromate and dilute sulfuric adic, when heated under refulx

Question 4

observation when aldehydes are oxidised

Answer 4

colour change from orange to green and chromium is orange but reduced to green Cr3+

Question 5

fehlings test

Answer 5

add fehlings solution and heat gently.
only aldehydes will be oxidised into carboxylic acids. blue to red precipitate

Question 6

tollens test

Answer 6

tollens reagent added and heat gently.
only aldehydes are oxidised to carboxylic acids.
a silver mirror will form around the test tube

Question 7

reduction of carbonyls

Answer 7

aldehydes are reduced to primary alcohols.
ketones are reduced to secondary alcohols.
NaBH4 or LiAlH4 in aq ethanol.
nucleophilic addition mechanism

Question 8

addition of HCN to carbonyls

Answer 8

form hydroxynitrile.
KCN reagent and dilute H2SO4
room temp + pressure
nucleophilic addition

Question 9

harm of HCN/KCN

Answer 9

HCN is not used as it is a toxic gas. and does not fully ionise as it is a weak acid
KCN is still toxic but will completely ionise as there is a greater CN- ion

Question 10

how does nucleophilic addition result in a racemic mixture

Answer 10

addition of HCN to aldehydes and ketones when the planar carbonyl group is approached equally from both sides by HCN, as enantiomers are formed.