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Chapter 6: Problem 184

In the following question two statements (Assertion) A and Reason (R) are given. Mark a. if \(\mathrm{A}\) and \(\mathrm{R}\) both are correct and \(\mathrm{R}\) is the correct explanation of \(\mathrm{A}\); b. if \(A\) and \(R\) both are correct but \(R\) is not the correct explanation of A; c. \(\mathrm{A}\) is true but \(\mathrm{R}\) is false; d. A is false but \(\mathrm{R}\) is true, e. A and \(R\) both are false. (A): The voltage of mercury cell remains constant for longer period of time. \((\mathbf{R}):\) It is because net cell reaction does not involve any ion.

Short Answer

Expert verified
Option c: (A) is true but (R) is false.

Step by step solution

01

Analyze Assertion (A)

The assertion (A) states that the voltage of a mercury cell remains constant for longer periods of time. This is a true statement. Mercury cells are known for their stable output voltage during their discharge period.
02

Analyze Reason (R)

The reason (R) claims that the voltage remains constant because the net cell reaction does not involve any ions. This is incorrect because the discharging process in a mercury cell does involve ionic reactions as they are electrochemical cells.
03

Evaluate the Connection Between A and R

Since the assertion (A) is true but the reason (R) is false, (R) cannot be the correct explanation for (A). The constancy in voltage is due to the efficient electrochemical reactions that occur in the cell, not the absence of ions in the reaction.
04

Determine the Correct Answer

Based on the analysis, (A) is true, but (R) is false. Therefore, the correct choice is option c.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Mercury Cell
Mercury cells are types of electrochemical cells known for their reliable and consistent voltage output over time. Unlike other batteries that may experience a rapid voltage drop, mercury cells deliver a stable voltage until almost fully depleted.
This characteristic makes them suitable for use in devices requiring a consistent power supply, such as watches and hearing aids. Mercury cells utilize a reaction between zinc and mercuric oxide, which allows for this steady voltage maintenance.
Despite their efficiency, the environmental concerns associated with mercury usage have led to restrictions on their production.
Voltage Stability
In electrochemical cells like mercury cells, voltage stability refers to the ability of the cell to maintain a constant voltage level during its operating life. This feature is crucial for the performance of devices that depend on consistent power levels.
The stable voltage of a mercury cell results from a well-controlled chemical reaction between zinc and mercuric oxide, which undergoes oxidation and reduction, respectively. These reactions occur at a balanced rate, ensuring that the cell discharge maintains a steady voltage.
This stability makes mercury cells highly reliable in their specific applications, distinguishing them from other battery types that may suffer significant voltage fluctuation during use.
Ionic Reactions
Ionic reactions play a significant role in the function of electrochemical cells. These reactions involve the transfer of electrons between ions in the electrolyte and the electrodes of the cell.
In a mercury cell, the primary reactions involve the oxidation of zinc ( Zn ightarrow Zn^{2+} + 2e^- ) and reduction of mercuric oxide ( HgO + H_2O + 2e^- ightarrow Hg + 2OH^- ). These reactions result in a flow of electrons, effectively generating electricity.
Far from being absent, ionic reactions are crucial for the operation of mercury cells and many other types of batteries, as they enable the conversion of chemical energy into electrical energy. This highlights the important role ions play in maintaining the cell's function and stability.

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Most popular questions from this chapter

In the following question two statements (Assertion) A and Reason (R) are given. Mark a. if \(\mathrm{A}\) and \(\mathrm{R}\) both are correct and \(\mathrm{R}\) is the correct explanation of \(\mathrm{A}\); b. if \(A\) and \(R\) both are correct but \(R\) is not the correct explanation of A; c. \(\mathrm{A}\) is true but \(\mathrm{R}\) is false; d. A is false but \(\mathrm{R}\) is true, e. A and \(R\) both are false. (A): Cell constant is the E.M.F. of a cell. (R): Cell constant is determined by using saturated KCl solution

In the following question two statements (Assertion) A and Reason (R) are given. Mark a. if \(\mathrm{A}\) and \(\mathrm{R}\) both are correct and \(\mathrm{R}\) is the correct explanation of \(\mathrm{A}\); b. if \(A\) and \(R\) both are correct but \(R\) is not the correct explanation of A; c. \(\mathrm{A}\) is true but \(\mathrm{R}\) is false; d. A is false but \(\mathrm{R}\) is true, e. A and \(R\) both are false. (A): The mobility of sodium ion is lower than that of potassium ion. \((\mathbf{R}):\) The ionic mobilities depend upon the effective radius of the ion.

Which is/are true for standard electrode potentials? a. \(\mathrm{E}^{\circ}\) for oxidation is the negative of \(\mathrm{E}^{\circ}\) for reduction. b. Cell constituents are in their standard states. c. The potential for the standard hydrogen electrode is chosen to be \(+1.00 \mathrm{~V}\). d. The half reactions are written as reductions.

The standard reduction potentials of \(\mathrm{Fe} / \mathrm{Fe}^{2+}\) and \(\mathrm{Fe}^{2+} / \mathrm{Fe}^{3+}\) are \(-0.44 \mathrm{~V}\) and \(0.77 \mathrm{~V}\) respectively. The reduction potential of \(\mathrm{Fe} / \mathrm{Fe}^{3+}\) couple is a. \(0.11 \mathrm{~V}\) b. \(0.037 \mathrm{~V}\) c. \(-0.11 \mathrm{~V}\) d. \(-0.037 \mathrm{~V}\)

In the following question two statements (Assertion) A and Reason (R) are given. Mark a. if \(\mathrm{A}\) and \(\mathrm{R}\) both are correct and \(\mathrm{R}\) is the correct explanation of \(\mathrm{A}\); b. if \(A\) and \(R\) both are correct but \(R\) is not the correct explanation of A; c. \(\mathrm{A}\) is true but \(\mathrm{R}\) is false; d. A is false but \(\mathrm{R}\) is true, e. A and \(R\) both are false. (A): When acidified zinc sulphate solution is electrolyzed between zinc electrodes. It is zinc that is deposited at the cathode and hydrogen evolution does not take place (R): The electrode potential of zinc is more negative than hydrogen as the overvoltage for hydrogen evolution on zinc is quite large.
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