Chemistry Aldehydes & Ketones ETEA 2022
PMDC Verified Question 34 of 94
Benedict's solution is the combination of:
A
\( Cu(OH)_2 \) + \( NaOH \) + Tartaric acid (\( C_4H_6O_6 \))
B
\( Cu(OH)_2 \) + \( NaOH \) + Citric acid (\( C_6H_8O_7 \))
C
\( Ag(NH_3)_2OH \) + \( NaOH \) + \( H_2SO_4 \)
D
\( NaCl \) + \( NaOH \) + Citric acid
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: \( Cu(OH)_2 \) + \( NaOH \) + Citric acid (\( C_6H_8O_7 \))
Concept:

Both Benedict's and Fehling's solutions use complexed Copper(II) ions as mild oxidizing agents, but they differ strictly in the chelating agent used to stabilize the copper.

Solution:

  • Benedict's reagent utilizes the citrate ion (from Citric acid) as the complexing agent in an alkaline solution (\( Na_2CO_3 \) or \( NaOH \)) to prevent the precipitation of Copper(II) hydroxide.


  • Therefore, it is a mixture containing Copper ions, a strong base, and Citric acid.


Why other options are incorrect:

Option A describes Fehling's solution, which uses tartrate ions (Rochelle salt) instead of citrate. Option C describes Tollens' reagent (silver based). Option D lacks the active oxidizing agent (copper).

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