Oxidation of alcohols

Question 1

What is the colour change that occurs when using K2CR2O7 in oxidation of alcohols

Answer 1

Orange to Green

Question 2

Explain the colour change when using K2CR2O7 in oxidation of alcohols

Answer 2

As K2CR2O7 oxidises alcohols/aldehydes it itself is reduced. Reduced from the Cr2o7 2- ion which is orange in aqueous solution to the Cr3+ ion which is green in aqueous solution

Question 3

What makes Fehling’s blue

Answer 3

Cu2+ ion

Question 4

What is the formula of the brick red ppt that forms when aldehydes are tested by Fehling’s

Answer 4

CuO

Question 5

How do you make Tollen’s

Answer 5

Add a few drops of NaOH to Silver Nitrate until a light brown ppt forms
Redissolve ppt with dilute ammonia

Question 6

What ion in Tollen’s is reduced by aldehydes

Answer 6

Ag(NH3)2+

Question 7

What is the positive result for aldehydes with the two reagents

Answer 7

Fehlings - blue to red ppt
Tollen’s colourless to silver mirror