exam questions Flashcards
describe suitable chemical tests with observations that would confirm the presence of a ketone, aldehyde and alkene (4)
- ketone = orange ppt in 2,4 DNP
- no result with tollens reagent
- aldehyde = silver mirror with tollens reagent
- alkene = decolourises bromine water
what is the name of the mechanism when an aldehyde reacts with NaCN and H+ ? (1)
nucleophilic addition
explain why nucleophilic addition involves heterolytic fission (2)
- both electrons go to one atom
- the covalent bond breaks
what is produced when a ketone reacts with NaBH4?
alcohol
what are the reagents for the reaction of an alcohol to haloalkane?
- NaBr
- H2SO4
what are the reagents for the reaction of a haloalkane to an amine?
- NH3
- ethanol
what is the reagent for a reaction of an amine to a salt?
HCl
what is produced when a nitrile reacts with excess H2/Ni?
amine
suggest a suitable chemical test to confirm that a compound contains an unsaturated carbon chain (1)
Br2 decolourises
describe a chemical test to confirm that a compound contains an aldehyde functional group (1)
- tollens reagent
- silver mirror
describe a chemical test to confirm the presence of a carbonyl group. how can 2 products be distinguished? (3)
- 2,4 DNP
- orange precipitate
- measure melting points and compare to known data values
in a nucleophilic substitution reaction of haloalkane to nitrile, where do the dipoles and curly arrows go? (2)
- from lone pair on CN to carbon in haloalkane
- from carbon in haloalkane to the halide bond
- pos on carbon, neg on halide
- produces a nitrile and Cl-
what reacts with NaCN to produce an hydroxynitrile? (1)
ketone
what is the reagent for the reaction of hydroxynitrile to carboxylic acid? (1)
HCl
what are the reagents for the reactions of hydroxynitriles to amines? (1)
- H2
- Ni catalyst
explain why an amine can react with dilute HCl to form a salt (1)
- it is a base
- the lone pair accepts a proton
suggest why a compound can be biodegradable (1)
polar bonds can be hydrolysed
state the reagent, observations and equation for the test for carboxylic acids (2)
- sodium carbonate
- effervescence
- RCOOH + Na2CO3–> RCOONa + CO2 + H2O
state the reagent, observations and equation for the test for aldehydes (2)
- tollens
- silver mirror
- RCHO + [O] –> RCOOH
state the reagent and observations for the test of ketones (1)
- 2,4 DNP
- orange precipitate
state the reagent and observations that can be used to identify the products of ester hydrolysis (1)
- acidified K2Cr2O7
- orange to green solution
- is positive for the alcohol
what is produced when a compound is oxidised with potassium dichromate, where the product has a positive test with tollens? (1)
primary alcohol
suggest a reagent that could be used in the reaction of a hydroxynitrile to a carboxylic acid (1)
H2SO4 / HCl
how does a hydroxide ion act as a nucleophile? (1)
donates a pair of electrons
what is the product when an aldehyde reacts with tollens reagent under acidic conditions? (1)
carboxylic acid
what is the product when an aldehyde reacts under alkaline conditions? (1)
salt
explain what is happening to the electron pairs and bonds in a nucleophilic addition reaction of carbonyls (3)
- nucleophile attracted to delta pos carbon, forming a dative covalent bond
- the electron pair is broken
- the electrons are now on the O
what is the organic product formed when butanal reacts with tollens reagent? (1)
butanoic acid
outline how mixtures containing orange precipitates from 2,4 DNP can be used to distinguish between butanal and butanone (3)
- purify/crystallise ppt
- measure melting points
- compare to known data values
why does the tollens reagent test give a different result with aldehydes than ketones? (1)
aldehydes are oxidised to carboxylic acids
why do ketones not give the silver mirror product when reacting with tollens reagent?
- tollens is a mild oxidising agent
- ketones do not have H on C=O so are less easily oxidised than aldehydes
explain what happens to the tollens reagent and aldehyde in a reaction (2)
- silver ions reduced
- aldehyde oxidised
