Question

When a solution of \(\mathrm{AgNO}_{3}(1 \mathrm{M})\) is electrolyzed using platinum anode and copper cathode. What are the products obtained at two electrodes? Given : \(E_{\mathrm{Cu}^{2+}}^{\circ} \mathrm{Cu}=+0.34\) volt; \(\quad E_{\mathrm{O}_{2}, \mathrm{H}^{+} \mid \mathrm{H}_{2} \mathrm{O}}^{\circ}=+1.23\) volt \(; \quad E_{\mathrm{H}^{+} \mid \mathrm{H}_{2}}^{\circ}=+0.0\) volt; \(E_{\mathrm{Ag}^{+} \mid \mathrm{Ag}}^{\circ}=+0.8 \mathrm{volt}\) (a) \(\mathrm{Cu} \longrightarrow \mathrm{Cu}^{2+}\) at anode; \(\mathrm{Ag}^{+} \longrightarrow \mathrm{Ag}\) at cathode (b) \(\mathrm{H}_{2} \mathrm{O} \longrightarrow \mathrm{O}_{2}\) at anode; \(\mathrm{Cu}^{2+} \longrightarrow \mathrm{Cu}\) at cathode (c) \(\mathrm{H}_{2} \mathrm{O} \longrightarrow \mathrm{O}_{2}\) at anode; \(\mathrm{Ag}^{+} \longrightarrow \mathrm{Ag}\) at cathode (d) \(\mathrm{NO}_{3}^{-} \longrightarrow \mathrm{NO}_{2}\) at anode; \(\mathrm{Ag}^{+} \longrightarrow \mathrm{Ag}\) at cathode

Short answer

The products obtained at the two electrodes are: Ag at the cathode and O2 at the anode.

Step-by-step solution

Identify Possible Reactions at Anode and Cathode

During the electrolysis of AgNO3 solution, the following reactions may occur: at the anode, Ag or H2O can be oxidized, and at the cathode, Ag+ or H2O may be reduced. The standard electrode potentials indicate the likelihood of each reaction occurring.

Apply the Standard Electrode Potentials

The standard electrode potentials for the possible reactions are: E_Ag+|Ag is +0.80 V (reduction potential), E_O2,H+|H2O is +1.23 V (oxidation potential of water to oxygen), E_Cu2+|Cu is +0.34 V (reduction potential), and E_H+|H2 is 0.00 V (standard hydrogen electrode). Since electrolysis favors reactions with lower reduction potential at the cathode and higher oxidation potential at the anode, Ag+ will likely get reduced to Ag at the cathode, and water will likely get oxidized to O2 and H+ at the anode. The involvement of Cu or NO3- is less likely due to their potentials.

Determine the Products at Each Electrode

Based on the standard electrode potentials: At the cathode, reduction of Ag+ ions to Ag solid is favored (+0.80 V > 0.34 V). At the anode, oxidation of water to oxygen is favored over the oxidation of Ag to Ag+ (1.23 V > 0.80 V).

Confirm the Most Favorable Reaction for Electrolysis

Given the potential values and the setup (platinum anode and copper cathode), the most probable reactions during the electrolysis of 1 M AgNO3 solution are: Cathode: Ag+ to Ag Anode: H2O to O2 and H+ The reaction involving copper or nitrate is not favorable due to their less positive oxidation potential or less negative reduction potential compared to the competing reactions.

Key concepts

Standard Electrode Potential

Understanding the standard electrode potential is key in predicting the outcome of electrolysis, as well as other electrochemical processes. It's essentially a measure of the tendency of a chemical species to gain or lose electrons and become reduced or oxidized. This value is relative to the standard hydrogen electrode, which is arbitrarily given a potential of 0.00 volts.
Electrode potentials are not only academic concepts but also have practical applications. For instance, in the electrolysis problem we're considering, knowing the standard electrode potential of Ag/Ag+, O2/H2O, and Cu2+/Cu helps us predict which substances will be oxidized or reduced. The rule of thumb is that the reaction with the higher reduction potential will occur at the cathode, and the one with the higher oxidation potential will occur at the anode. Therefore, from the given options, we can determine that Ag+ will be reduced to Ag at the cathode because it has a higher reduction potential (+0.80 V) compared to copper's ability to get reduced (+0.34 V).

Redox Reactions

Electrolysis involves redox reactions, where reduction (gain of electrons) and oxidation (loss of electrons) occur simultaneously. Knowing the redox fundamentals allows you to dissect electrolysis processes and understand the electron flow from anode to cathode.
In our example, at the cathode, electrons are gained by Ag+ ions (reduction), while at the anode, water molecules lose electrons (oxidation) to form oxygen and protons. This simultaneous transfer of electrons highlights the quintessence of redox reactions in electrochemistry.

Understanding Electron Flow

Electrons move from the anode to the cathode. The substance that oxidizes loses electrons and the one that reduces gains them. By applying these principles, we can identify the correct products in an electrolysis setting.

Galvanic Cells

While our textbook exercise centers around electrolysis, understanding galvanic cells can help clarify why certain reactions are more favorable. Galvanic cells are electrochemical cells that convert chemical energy into electrical energy through spontaneous redox reactions. The cell has two electrodes – the anode is the electrode where oxidation occurs, and the cathode is where reduction happens, exactly opposite to the anode and cathode in the context of electrolysis.
A pivotal concept in galvanic cells is that the electrode with the higher standard electrode potential becomes the cathode, while the one with the lower potential becomes the anode. Although our problem is about non-spontaneous electrolysis, the principles governing electrode potentials are the same.

JEE Chemistry Problems

Aspiring students tackling JEE Chemistry problems need to be proficient with concepts like electrode potentials and redox reactions, which are integral to the field of electrochemistry. JEE problems require a deep understanding and keen application of these concepts. They often involve complex scenarios where multiple reactions are possible, and the most favorable outcome must be determined, just like in our electrolysis exercise.

Tackling JEE Questions

A systematic approach is crucial – first understand the core concepts, then apply them to the given problem. For example, by knowing that we're dealing with electrolysis, students can assess the likelihood of different reactions based on the standard electrode potentials, allowing them to eliminate less probable options and recognize the accurate products at the electrodes.