Saturated solution of is used to make 'salt bridge' because — Electrochemistry Chemistry Question

💡 Solution & Explanation

Step 1 - Function and Purpose of a Salt Bridge A salt bridge completes the internal electrical circuit of a galvanic cell and maintains electrical neutrality in both half-cells by allowing ion migration. Step 2 - Role of Ionic Velocity in Preventing Liquid Junction Potential If the cations and anions of the salt bridge electrolyte migrate at different speeds, a liquid junction potential develops at the interface, opposing the cell EMF. To minimize this, both ions must migrate at nearly equal velocities (equal transport numbers $\approx 0.5$ each). Step 3 - Analyzing $\ce{KNO3}$ as a Salt Bridge Electrolyte For $\ce{KNO3}$: $$\lambda^\circ(\ce{K^+}) \approx 73.5\,\Omega^{-1}\text{ cm}^2\text{ mol}^{-1}$$ $$\lambda^\circ(\ce{NO3^-}) \approx 71.4\,\Omega^{-1}\text{ cm}^2\text{ mol}^{-1}$$ Their ionic velocities are nearly equal, so transport numbers are approximately $0.5$ each. This prevents liquid junction potential. Step 4 - Evaluation of the Options * **Option (A)** is incorrect — $\ce{K^+}$ velocity is NOT significantly greater than $\ce{NO3^-}$. * **Option (B)** is incorrect — $\ce{NO3^-}$ velocity is NOT significantly greater than $\ce{K^+}$. * **Option (C)** is correct — velocities of both $\ce{K^+}$ and $\ce{NO3^-}$ are nearly equal. * **Option (D)** is incorrect — high solubility is useful but NOT the primary electrochemical reason. $$\text{Correct Option: } \boxed{\text{C}}$$