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Chapter 6: Problem 218

Saturated solution of \(\mathrm{KNO}_{3}\) is used to make 'salt bridge' because: a. velocity of \(\mathrm{K}^{+}\)is greater than that of \(\mathrm{NO}_{3}^{-}\). b. velocity of \(\mathrm{NO}_{3}^{-}\)is greater than that of \(\mathrm{K}^{+}\). c. velocities of both \(\mathrm{K}^{+}\)and \(\mathrm{NO}_{3}^{-}\)are nearly the same. d. \(\mathrm{KNO}_{3}\) is highly soluble in water.

Short Answer

Expert verified
The velocities of both \(\mathrm{K}^{+}\) and \(\mathrm{NO}_{3}^{-}\) are nearly the same.

Step by step solution

01

Understanding the question

The question is asking for a reason why a saturated solution of \(\mathrm{KNO}_{3}\) is used to make a 'salt bridge.' There are four options provided. We need to analyze which option correctly explains the use of \(\mathrm{KNO}_{3}\) in salt bridges.
02

Analyze each option

We need to consider the properties of \(\mathrm{KNO}_{3}\) and its ions. \(\mathrm{KNO}_{3}\) consists of \(\mathrm{K}^{+}\) and \(\mathrm{NO}_{3}^{-}\). Typically in a salt bridge, the cation and anion need to migrate at similar speeds to maintain electrical neutrality effectively.
03

Compare ion velocities

Options (a) and (b) suggest that one ion has a significantly different velocity than the other, either \(\mathrm{K}^{+}\) being faster or \(\mathrm{NO}_{3}^{-}\) being faster. If either ion were significantly faster, it could cause a charge imbalance and impact the stability of the potential between electrochemical cells.
04

Evaluate nearly equal ion velocities

Option (c) suggests that the velocities of \(\mathrm{K}^{+}\) and \(\mathrm{NO}_{3}^{-}\) are nearly the same. This would be beneficial in a salt bridge because it helps maintain a stable flow of charge without causing an imbalance.
05

Consider the solubility

Option (d) states \(\mathrm{KNO}_{3}\) is highly soluble in water. While this property is useful for dissolving the salt to form a solution, it does not directly address the reason for using it in salt bridges compared to other soluble salts.
06

Conclusion

The most appropriate reason why \(\mathrm{KNO}_{3}\) is chosen for salt bridges is because the velocities of \(\mathrm{K}^{+}\) and \(\mathrm{NO}_{3}^{-}\) are nearly the same. This ensures the proper functioning of the salt bridge by preventing a charge imbalance.

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Key Concepts

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

Understanding Ionic Velocity
Ionic velocity refers to the speed at which ions move through a solution. This movement is essential in various chemical processes, especially in maintaining charge balance in solutions such as salt bridges in electrochemical cells. Factors that affect ionic velocity include:
  • Ion size: Smaller ions usually move faster than larger ones due to less resistance in the medium.
  • Charge: Higher charged ions will likely experience greater electrostatic attraction or repulsion, affecting their speed.
  • Medium's Viscosity: More viscous solutions slow down ionic movement while less viscous ones do the opposite.
In salt bridges, when the cations and anions have similar ionic velocities, it helps maintain electrical neutrality, which is crucial to the proper functioning of electrochemical cells.
Role of Electrochemical Cells
Electrochemical cells are devices that convert chemical energy into electrical energy through redox reactions. They are fundamental components in batteries, galvanic cells, and fuel cells. Each cell consists of two electrodes immersed in an electrolyte and connected by a salt bridge. Here's why they are important:
  • Energy Conversion: They enable the direct conversion of chemical energy into electricity, bypassing the inefficiencies of mechanical energy conversion in traditional generators.
  • Redox Reactions: Electrochemical cells facilitate redox reactions where oxidation and reduction processes occur at different electrodes, generating a flow of electrons.
  • Salt Bridge's Role: The salt bridge maintains electrical neutrality within the cell, ensuring continuous electron flow by balancing charges as ions migrate through it.
Knowing the mechanics of electrochemical cells is vital when understanding why potassium nitrate is preferred in a salt bridge, mainly due to maintaining ionic flow and charge balance.
Importance of Potassium Nitrate in Salt Bridges
Potassium nitrate (\(\text{KNO}_3\)) is often used in salt bridges for its excellent properties, making it an ideal choice in electrochemical setups. Reasons for its use:
  • Solubility: \(\text{KNO}_3\) is highly soluble in water, allowing it to create a conductive pathway easily.
  • Ionic Balance: The similar ionic velocities of \(\text{K}^+\) and \(\text{NO}_3^-\) ions help reduce the risk of charge buildup, preventing an imbalance.
  • Inertness: It typically doesn't react with other components of the cell, preserving the integrity of the electrochemical reaction.
  • Versatility: It can be used across different electrochemical systems without altering the essential reactions occurring within the cell.
The inherent properties of potassium nitrate thus make it crucial in maintaining stability and efficiency in electrochemical cells by functioning exceptionally well in a salt bridge.
Ensuring Electrical Neutrality
Electrical neutrality in an electrochemical cell is the balance of charge across the entire system. It's critical in guaranteeing that the electrochemical processes continue unhindered. Key points:
  • Balance of Charges: As electrons flow through the external circuit, ions need to compensate by moving in the opposite direction through the salt bridge.
  • Stable ionic movement: When the cations and anions have nearly similar velocities, it ensures that neither positive nor negative charges accumulate excessively on one side of the cell.
  • Continuity of Reaction: Maintaining a neutral charge balance keeps the electrochemical reactions active by allowing a continuous flow of ions and electrons.
  • Prevention of Precipitation: Charge imbalance might lead to unwanted chemical precipitation in the electrolyte, disrupting the reaction.
The choice of materials like potassium nitrate, which maintains consistent ionic flow, ensures that the system works smoothly by preventing charge disparities.

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Most popular questions from this chapter

\(2 \mathrm{Hg} \rightarrow \mathrm{Hg}_{2}^{2+}, \mathrm{E}^{\circ}=+0.855 \mathrm{~V}\) \(\mathrm{Hg} \rightarrow \mathrm{Hg}^{2+}, \mathrm{E}^{\circ}=+0.799 \mathrm{~V}\) Equilibrium constant for the reaction \(\mathrm{Hg}+\mathrm{Hg}^{2+} \rightarrow \mathrm{Hg}_{2}{ }^{2+}\) at \(27^{\circ} \mathrm{C}\) is a. 79 b. 89 c. 69 d. \(82.9\)

For the electrochemical cell, \(\mathrm{M}\left|\mathrm{M}^{+} \| \mathrm{X}^{-}\right| \mathrm{X}, \mathrm{E}^{\circ}\) \(\mathrm{M}^{+}{ }_{M}=0.44 \mathrm{~V}\) and \(\mathrm{E}_{\mathrm{X} \mathrm{X}}^{\mathrm{o}}=0.33 \mathrm{~V}\) From these data one can deduce that a. \(\mathrm{M}+\mathrm{X} \rightarrow \mathrm{M}^{+}+\mathrm{X}^{-}\)is the spontaneous reaction b. \(\mathrm{M}^{+}+\mathrm{X}^{-} \rightarrow \mathrm{M}+\mathrm{X}\) is spontaneous reaction c. Ecell \(=0.77 \mathrm{~V}\) d. Ecell \(=-0.77 \mathrm{~V}\)

For a galvanic cell that uses the following two half reactions, $$ \begin{array}{r} \mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}(\mathrm{aq})+14 \mathrm{H}^{+}(\mathrm{aq})+6 \mathrm{e}^{-} \rightarrow \\ 2 \mathrm{Cr}^{3+}(\mathrm{aq})+7 \mathrm{H}_{2} \mathrm{O} \text { (l) } \end{array} $$ \(\mathrm{Pb}(\mathrm{s}) \rightarrow \mathrm{Pb}^{2+}(\mathrm{aq})+2 \mathrm{e}^{-}\) How many moles of \(\mathrm{Pb}\) (s) are oxidized by one mole of \(\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-} ?\) a. 6 b. 4 c. 3 d. 2

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): If standard reduction potential for the reaction \(\mathrm{Ag}^{+}+\mathrm{e}^{-} \rightarrow \mathrm{Ag}\) is \(0.80\) volts then for the reaction \(3 \mathrm{Ag}^{+}+3 \mathrm{e}^{-} \rightarrow 3 \mathrm{Ag}\) it will be \(2.4\) volts \((\mathbf{R})\) : If concentration is increased, reduction electrode potential is increased.

If \(\mathrm{E}_{\mathrm{MnO4}-\mathrm{Mn} 2+}^{\mathrm{o}}=1.51 \mathrm{~V}\) and \(\mathrm{E}^{\circ} \mathrm{MnO}_{2} / \mathrm{Mn}^{2+}=1.23\) \(\mathrm{V}\), the \(\mathrm{E}_{\mathrm{M}=04-\mathrm{Mn} \mathrm{O}_{2}}^{\mathrm{o}}\) is a. \(+1.69 \mathrm{~V}\) b. \(-1.69 \mathrm{~V}\) c. \(-3.38 \mathrm{~V}\) d. \(+0.845 \mathrm{~V}\)
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