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Question #44082

Difficulty: 8/10 | 🟢 Free

The Question

An extremely dilute aqueous solution of \ce{HCl} is prepared at 298 K298\text{ K} with a concentration of 1.0×10−7 M1.0 \times 10^{-7}\text{ M}. The limiting molar conductivities at 298 K298\text{ K} are λ\ceH+∘=350 S cm2 mol−1\lambda^\circ_{\ce{H^+}} = 350\text{ S cm}^2\text{ mol}^{-1}, λ\ceOH−∘=200 S cm2 mol−1\lambda^\circ_{\ce{OH^-}} = 200\text{ S cm}^2\text{ mol}^{-1}, and λ\ceCl−∘=75 S cm2 mol−1\lambda^\circ_{\ce{Cl^-}} = 75\text{ S cm}^2\text{ mol}^{-1}. The ionic product of water is Kw=1.0×10−14K_w = 1.0 \times 10^{-14}. Calculate the true specific conductance (κsol\kappa_{sol}) of this solution, and the apparent molar conductivity of \ce{HCl} (Λm,app\Lambda_{m, app}) if it is calculated using the standard formula Λm,app=1000×(κsol−κ\ceH2O)C\ceHCl\Lambda_{m, app} = \frac{1000 \times (\kappa_{sol} - \kappa_{\ce{H_2O}})}{C_{\ce{HCl}}}, where C\ceHClC_{\ce{HCl}} is the molarity of \ce{HCl} and κ\ceH2O\kappa_{\ce{H_2O}} is the specific conductance of pure water. (Use 5≈2.236\sqrt{5} \approx 2.236)

Options

  • A.

    κsol=7.65×10−8 S cm−1\kappa_{sol} = 7.65 \times 10^{-8}\text{ S cm}^{-1}, Λm,app=215 S cm2 mol−1\Lambda_{m, app} = 215\text{ S cm}^2\text{ mol}^{-1}

  • B.

    κsol=9.75×10−8 S cm−1\kappa_{sol} = 9.75 \times 10^{-8}\text{ S cm}^{-1}, Λm,app=425 S cm2 mol−1\Lambda_{m, app} = 425\text{ S cm}^2\text{ mol}^{-1}

  • C.

    κsol=4.25×10−8 S cm−1\kappa_{sol} = 4.25 \times 10^{-8}\text{ S cm}^{-1}, Λm,app=425 S cm2 mol−1\Lambda_{m, app} = 425\text{ S cm}^2\text{ mol}^{-1}

  • D.

    κsol=7.65×10−8 S cm−1\kappa_{sol} = 7.65 \times 10^{-8}\text{ S cm}^{-1}, Λm,app=765 S cm2 mol−1\Lambda_{m, app} = 765\text{ S cm}^2\text{ mol}^{-1}

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Numerical_Precision

Improve calculation stamina and avoid rounding errors in high-stakes competitive examinations.

Concepts Behind This Question

pH of Extremely Dilute Solutions|Kohlrausch Law Infinite Dilution

Why This Question Is Tricky

Common Mistakes

Tests the assumption that conductivities of mixed electrolytes are strictly additive.

At extremely low concentrations, the common ion effect suppresses water's auto-protolysis, meaning κsol≠κ\ceHCl+κ\ceH2O\kappa_{sol} \neq \kappa_{\ce{HCl}} + \kappa_{\ce{H_2O}}.

Subtracting the conductivity of pure water from the solution's conductivity yields an anomalously low apparent molar conductivity for the solute.

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Question Information

SubjectChemistry
ChapterEquilibrium - Class 11 Part 1
ConceptpH of Extremely Dilute Solutions
Difficulty8
Cognitive Load7
Target Solve Time160 sec
AccessFree