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प्रश्न
Discuss the variation of conductivity and molar conductivity with concentration.
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उत्तर
Both conductivity and molar conductivity change with changes in the concentration of the electrolyte. Conductivity always decreases as the concentration of both weak and strong electrolytes decreases. This can be explained by the fact that with dilution, the number of ions carrying electric current per unit volume decreases. The conductivity of a solution at any concentration is the conductivity of a unit volume of the solution placed between two platinum electrodes having a unit cross-sectional area and situated at a unit distance from each other.
This is clear from the following equation:
C = `(kappa A)/l` = κ ...(Both A and l are in appropriate units m or cm)
The molar conductivity of a solution at a given concentration is the conductivity of volume (V) of the solution containing one mole of electrolyte dissolved in it and placed between two electrodes of cross-sectional area (A), located at a unit distance from each other. So,
Plot of c1/2 versus molar conductivity for potassium chloride (a strong electrolyte) in aqueous solution.
∧m = `(kappa A)/l` = κ
Since l = 1 and A = V (volume in which one mole of electrolyte is dissolved)
∧m = κ V
Molar conductivity increases with decreasing concentration. This is because the total volume (V) in which one mole of electrolyte is present also increases. It has been found that, upon dilution of the solution, the increase in volume is much greater than the decrease in κ.
Strong Electrolytes: For strong electrolytes, the value of ∧m increases gradually with dilution, and it can be represented by the following equation:
∧m = `Lambda_m^0 - Ac^(1//2)`
It can be seen that if ∧m is plotted against c1/2, we get a straight line with intercept A and slope equal to ‘A’. The value of constant ‘A’ at a given solvent and temperature depends on the type of electrolyte, i.e., on the charges of the cation and anion produced on dissociation of the electrolyte in solution. Thus, NaCl, CaCl2, and MgSO4 are known as 1-1, 2-1 and 2-2 electrolytes, respectively. The value of ‘A’ is the same for all electrolytes of the same type.
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संबंधित प्रश्न
Define “Molar conductivity”.
State Kohlrausch’s law of independent migration of ions.
The molar conductivity of cation and anion of salt BA are 180 and 220 mhos respectively. The molar conductivity of salt BA at infinite dilution is_____________ .
(a) 90 mhos.cm2
(b) 110 mhos.cm2.mol-1
(c) 200 mhos.cm2.mol-1
(d) 400 mhos.cm2.mol-1
The conductivity of 0.20 mol L−1 solution of KCl is 2.48 × 10−2 S cm−1. Calculate its molar conductivity and degree of dissociation (α). Given λ0 (K+) = 73.5 S cm2 mol−1 and λ0 (C1−) = 76.5 S cm2 mol−1.
Calculate the degree of dissociation (α) of acetic acid if its molar conductivity (Λm) is 39.05 S cm2 mol−1.
(Given \[\ce{\lambda^{\circ}_{(H^+)}}\] = 349.6 S cm2 mol−1 and \[\ce{\lambda^{\circ}_{(CH_3COO^-)}}\] = 40.95 S cm2 mol−1)
How can you determine limiting molar conductivity, 0 m for strong electrolyte and weak electrolyte?
In the plot of molar conductivity (∧m) vs square root of concentration (c1/2) following curves are obtained for two electrolytes A and B : 
Answer the following:
(i) predict the nature of electrolytes A and B.
(ii) What happens on the extrapolation of ∧m to concentration approaching for electrolytes A and B?
Kohlrausch law of independent migration of ions states ____________.
\[\ce{\Lambda^0_m(NH4OH)}\] is equal to ______.
Why on dilution the m Λm of \[\ce{CH3COOH}\] increases very fast, while that of \[\ce{CH3COONa}\] increases gradually?
Assertion: Λm for weak electrolytes shows a sharp increase when the electrolytic solution is diluted.
Reason: For weak electrolytes degree of dissociation increases with dilution of solution.
Which of the following halogen acids is the strongest reducing agent?
The molar conductivity of 0.007 M acetic acid is 20 S cm2 mol−1. What is the dissociation constant of acetic acid? Choose the correct option.
\[\begin{array}{cc}
\end{array}\]\[\begin{bmatrix}
\ce{\Lambda^{\circ}_{H^+} = 350 S cm^2 mol^{-1}}\\
\ce{\Lambda^{\circ}_{CH_3COO^-} = 50 S cm^2 mol^{-1}}
\end{bmatrix}\]
The solubility of Co2[Fe(CN)6] in water at 25°C from the following data:
Conductivity of saturated solution of Co2[Fe(CN)6] = 2.06 × 10−6 ohm−1 cm−1 and that of water = 4.1 × 10−7 ohm−1 cm−1. The ionic molar conductivities of Co2+ and [Fe(CN)6]4− are 86 and 444 ohm−1 cm2 mol−1 respectively, is ______ × 10−6 mol/L.
Assertion (A): Molar conductivity decreases with increase in concentration.
Reason (R): When concentration approaches zero, the molar conductivity is known as limiting molar conductivity.
The resistance of a conductivity cell with a 0.1 M KCl solution is 200 ohm. When the same cell is filled with a 0.02 M NaCl solution, the resistance is 1100 ohm. If the conductivity of 0.1 M KCl solution is 0.0129 ohm-1 cm-1, calculate the cell constant and molar conductivity of 0.02 M NaCl solution.
