UPSC Combined Geo-Scientist, Mains · 2018 · Mains Paper II
Q1(l). Conductivity as an intensive property
Question
Why does conductivity of an ionic solution depend on temperature but not on its mass?
Answer in brief
Conductivity is an intensive property determined by ion concentrations, charges and mobilities; temperature changes ion mobility and sometimes ionisation.
Key points
- For a uniform solution, κ=Gℓ/A, where G is measured conductance and ℓ/A the cell geometry factor.
- Approximately κ=FΣᵢ|zᵢ|uᵢcᵢ. Ion number per unit volume, not total sample mass, determines the charge-carrier contribution.
- Increasing temperature usually lowers solvent viscosity and increases ionic mobility; it may also change dissociation and solvation. Thus conductivity is temperature-dependent.
- Conductance of a particular sample does depend on path length and cross-section. Conductivity and conductance must not be confused.
The full model answer
As written for the answer booklet: the diagram carries the working, the lines stay short. Read here only; it is not offered as a download.
CoversConductivity as an intensive propertyElectrochemistry
All parts of Question 1
- 1(a) Equal molecular speeds5 marks
- 1(b) Fugacity under repulsion5 marks
- 1(c) Wetting of glass5 marks
- 1(d) FCC particle count5 marks
- 1(e) Joule–Thomson cooling5 marks
- 1(f) Gibbs and Helmholtz changes5 marks
- 1(g) Equilibrium-constant conventions5 marks
- 1(h) Very dilute hydrochloric acid5 marks
- 1(i) Pressure controlling boiling5 marks
- 1(j) Primary kinetic salt effect5 marks
- 1(k) Heat of spontaneous adsorption5 marks
- 1(l) Conductivity as an intensive property5 marks
- 1(m) Anthracene photodimerization5 marks
- 1(n) Particle-in-a-box eigenvalue5 marks
- 1(o) Second Balmer line5 marks
- 1(p) Normal-mode counts5 marks