Junction Potential A 0.1 M NaCl solution was placed in contact with a 0.1 M [latex]NaNO_{3}[/latex] solution. Which side of the junction is positive?

Because [latex][Na^{+}][/latex] is equal on both sides, there is no net diffusion of [latex]Na^{+}[/latex] across the junction. However, [latex]Cl^{−}[/latex] diffuses into [latex]NaNO_{3}[/latex], and [latex]NO_{3}^{−}[/latex] diffuses into NaCl. The mobility of [latex]Cl^{−}[/latex] is greater than that of [latex]NO_{3}^{−}[/latex], so the NaCl region will be depleted of [latex]Cl^{−}[/latex] faster than the [latex]NaNO_{3}[/latex] region will be depleted of [latex]NO_{3}^{−}[/latex]. The [latex]NaNO_{3}[/latex] side will become negative, and the NaCl side will become positive. Test Yourself Which side of the 0.05 M NaCl | 0.05 M LiCl junction will be positive? ( Answer: LiCl) TABLE 14-2 Liquid junction potentials at 25°C Junction Potential (mV) 0.1 M NaCl | 0.1 M KCl −6.4 0.1 M NaCl | 3.5 M KCl −0.2 1 M NaCl | 3.5 M KCl −1.9 0.1 M HCl | 0.1 M KCl +27 0.1 M HCl | 3.5 M KCl +3.1 NOTE: A positive sign means that the right side of the junction becomes positive with respect to the left side.

Question 14.2: Junction Potential. A 0.1 M NaCl solution was placed in cont...

Quantitative Chemical Analysis

Junction Potential

A 0.1 M NaCl solution was placed in contact with a 0.1 M $NaNO_{3}$ solution. Which side of the junction is positive?

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Because $[Na^{+}]$ is equal on both sides, there is no net diffusion of $Na^{+}$ across the junction. However, $Cl^{−}$ diffuses into $NaNO_{3}$ , and $NO_{3}^{−}$ diffuses into NaCl. The mobility of $Cl^{−}$ is greater than that of $NO_{3}^{−}$ , so the NaCl region will be depleted of $Cl^{−}$ faster than the $NaNO_{3}$ region will be depleted of $NO_{3}^{−}$ . The $NaNO_{3}$ side will become negative, and the NaCl side will become positive.

Test Yourself Which side of the 0.05 M NaCl | 0.05 M LiCl junction will be positive?

(Answer: LiCl)

TABLE 14-2 Liquid junction potentials at 25°C
Junction	Potential (mV)
0.1 M NaCl \| 0.1 M KCl	−6.4
0.1 M NaCl \| 3.5 M KCl	−0.2
1 M NaCl \| 3.5 M KCl	−1.9
0.1 M HCl \| 0.1 M KCl	+27
0.1 M HCl \| 3.5 M KCl	+3.1