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UPSC Civil Services (Mains)

Chemistry optional

  • 2 papers
  • 250 marks each
  • 3 h per paper
  • 5 of 8 questions, Q1 and Q5 compulsory

Paper I covers physical and inorganic chemistry.

UPSC Civil Services (Mains), Chemistry optional · 2025 · Paper I

Q4(c). Molar conductivity and transport numbers of Ca(NO₃)₂

Question

The level of conductivity in a decimolar aqueous solution of calcium nitrate, which is a strong electrolyte, is measured as σ = 26.2 mS cm⁻¹ at 25 °C. Calculate the molar conductivity of the electrolyte, that of calcium ions and the transport numbers of the two types of ions present in the solution, with the data given below. Molar conductivity at infinite dilution in aqueous solution at 25 °C: λ°(Ca²⁺) = 11.9 mS m² mol⁻¹; λ°(NO₃⁻) = 7.14 mS m² mol⁻¹. [data table given in the paper]

Answer in brief

Λm = 26.2 mS m² mol⁻¹; λ(Ca²⁺) = 11.9 mS m² mol⁻¹; t(Ca²⁺) = 0.455, t(NO₃⁻) = 0.545.

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Coversmolar conductivityKohlrausch's lawtransport numberionic conductivitycalcium nitrate

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