Question

Tollen's reagent is used for the detection of aldehyde when a solution of $AgN{O}_3$ is added to glucose with $N{H}_{4}OH$ then gluconic acid is formed
$A{g}^{+}+e^{-}\to Ag;E_{red}^{+}=0.8V$
$C_6{H}_{12}{O}_6+H_{2}O\to$ Gluconic acid $\left(C_6{H}_{12}{O}_7\right)+2H^{+}+2e^{-}$
$E_{red}{}^{\circ }=-0.05V$
$Ag{\left(N{H}_3\right)}_2{}^{+}+e^{-}\to Ag(s)+2N{H}_3;E_{red}{}^{\circ }=0.337V$
[Use $2.303\times \frac{RT}{F}=0.0592$ and $\frac{F}{RT}=38.92$ at $398K]$
Ammonia is always is added in this reaction. Which of the following must be incorrect?

• A. $N{H}_3$ combines with $Ag+$ to form a complex.
• B. $Ag{\left(N{H}_3\right)}_2^{+}$is a stronger oxidising reagent than $A{g}^{+}.$
• C. In absence of $N{H}_3$, silver salt of gluconic acid is formed.
• D. $N{H}_3$ has affected the standard reduction potential of glucose/ gluconic acid electrode.

Answer 1

Answer: (D)

It is clear from the given reactions that $N{H}_3$ combines with $Ag$ to give $Ag\left(N{H}_3\right).$ Also, the value of $E_{\text{red }}0$ of $A{g}^{+}$is greater than $Ag\left(N{H}_3\right)$, which means it is a stronger oxidising agent than $A{g}^{+}$and in absence of ammonia, gluconic acid is formed. Therefore, the statement $(D)$ is incorrect as ammonia has no effect on the standard reduction potential of glucose/gluconic electrode.