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3.3.6 - organic analysis

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Total cards: 24•Content version: v4•Public deck•Updated: 8/1/2026

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#1
Front (Question)

how to distinguish aldehydes and ketone

Back (Answer)

aldehydes and ketones can be distinguished using oxidising agents

#2
Front (Question)

why can aldehydes and ketones be distinguished using oxidising agents

Back (Answer)

aldehydes are easily oxidised but ketones aren’t

#3
Front (Question)

TESTING FOR ALCOHOLS step 1

Back (Answer)

• add 10 drops of alcohol to 2cm^3 of acidified potassium dichromate solution in a test tube

#4
Front (Question)

TESTING FOR ALCOHOLS step 2

Back (Answer)

• warm the mixture gently in a hot water bath

#5
Front (Question)

TESTING FOR ALCOHOLS step 3

Back (Answer)

• watch for a colour change

#6
Front (Question)

TESTING FOR ALCOHOLS colour change for primary and secondary alcohols

Back (Answer)

potassium dichromate(VI) is reduced so colour changes from orange to green - orange dichromate(VI) ions are reduced - green chromium(III) ions are formed

#7
Front (Question)

equation for reduction of potassium dichromate(VI)

Back (Answer)

(Cr2,O7) 2- + 6e- + 14H+ = (2Cr) 3+ + 7H2O

#8
Front (Question)

TESTING FOR ALCOHOLS colour change for tertiary alcohols

Back (Answer)

no colour change so solution stays orange

#9
Front (Question)

testing for primary alcohols (carboxylic acid)

Back (Answer)

if you oxidise an alcohol under reflux and it tests positive for being a carboxylic acid, then it’s a primary alcohol

#10
Front (Question)

testing for primary alcohols (aldehyde)

Back (Answer)

if you oxidise an alcohol under distillation conditions and it tests positive for being an aldehyde, then its a primary alcohol

#11
Front (Question)

testing for secondary alcohols

Back (Answer)

if you oxidise an alcohol under reflux (or distillation) and it tests positive for being a ketone, then its a secondary alcohol

#12
Front (Question)

what is Fehling’s solution?

Back (Answer)

blue solution of complex copper(II) ions dissolved in sodium hydroxide

#13
Front (Question)

what is Benedict’s solution?

Back (Answer)

similar to Fehling’s but copper(II) ions are dissolved in sodium carbonate instead

#14
Front (Question)

TESTING ALDEHYDE/KETONE WITH BENEDICT’S/FEHLING’S stage 1

Back (Answer)

• add 2cm^3 of benedict’s or Fehling’s solution to a test tube

#15
Front (Question)

TESTING ALDEHYDE/KETONE WITH BENEDICT’S/FEHLING’S stage 2

Back (Answer)

• add 5 drops of the aldehyde or ketone to the test tube

#16
Front (Question)

TESTING ALDEHYDE/KETONE WITH BENEDICT’S/FEHLING’S stage 3

Back (Answer)

• put the test tube in a hot water bath for a few minutes to warm it up

#17
Front (Question)

TESTING ALDEHYDE/KETONE WITH BENEDICT’S/FEHLING’S what happens if it is a aldehyde

Back (Answer)

benedict’s and Fehling’s solution will both reduce to a brick red Cu2,O precipitate when warmed with an aldehyde colour change from blue to red

#18
Front (Question)

TESTING ALDEHYDE/KETONE WITH BENEDICT’S/FEHLING’S what happens if it is a ketone

Back (Answer)

no reaction happens with ketones so the solution stays blue

#19
Front (Question)

reduction of copper ions in Fehling’s/benedict’s solution

Back (Answer)

2(Cu)2+ + 2(OH)- + 2e- = Cu2,O + H2,O -copper(II) ions in Fehling’s/Benedict’s solution reduced - electrons come from oxidation of aldehyde - copper(I) ions form a brick red precipitate of copper(I) oxide

#20
Front (Question)

what does tollens’ reagent contain

Back (Answer)

a [Ag(NH3)2] + complex

#21
Front (Question)

TESTING ALDEHYDE/KETONE WITH TOLLENS’ stage 1

Back (Answer)

• put 2cm^3 of 0.1 moldm^-3 silver nitrate solution in a test tube

#22
Front (Question)

TESTING ALDEHYDE/KETONE WITH TOLLENS’ stage 2

Back (Answer)

• add a few drops of dilute sodium hydroxide solution. light brown precipitate should form

#23
Front (Question)

TESTING ALDEHYDE/KETONE WITH TOLLENS’ stage 3

Back (Answer)

• add drops of dilute ammonia solution until the brown precipitate dissolves completely - this solution is Tollens’ reagent

#24
Front (Question)

TESTING ALDEHYDE/KETONE WITH TOLLENS’ stage 4

Back (Answer)

• add a few drops of the aldehyde or ketone and warm the solution in a water bath