Chemistry Aldehydes & Ketones SET 2019
PMDC Verified Question 52 of 94
For the reaction sequence below, what is the final indication of the product N?

$$ H_3C-CH_2-OH \xrightarrow{K_2Cr_2O_7 / H_2SO_4} M \xrightarrow{AgNO_3 / NH_4OH} N $$
A
Blue precipitate
B
Silver mirror
C
Red precipitate
D
White precipitate
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: Silver mirror
Concept:

This sequence involves forming an aldehyde and then testing it with Tollens' reagent.

Solution:

  • Step 1: Ethanol (\( CH_3CH_2OH \)) is oxidized by acidified potassium dichromate. Assuming immediate distillation (standard context for M), the product M is Acetaldehyde (\( CH_3CHO \)).


  • Step 2: Compound M is reacted with ammoniacal silver nitrate (\( AgNO_3 / NH_4OH \)), which is Tollen's reagent.


  • Acetaldehyde reduces the Silver(I) ions to metallic silver (N), which coats the glass as a distinct Silver mirror.


Why other options are incorrect:

Red precipitate is the result of Fehling's or Benedict's test, not Tollens'. Blue and white precipitates are not associated with this specific reaction sequence.

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