Test: Conductance - 1 - Chemistry MCQ

• The cell constant is a multiplier constant specific to a conductivity sensor.
• The measured current is multiplied by the cell constant to determine the electrical conductivity of the solution.
• The cell constant, known as K, refers to a theoretical electrode consisting of two 1 cm square plates 1 cm apart.
• A cell constant has units of 1/cm (per centimeter), where the number refers to the ratio of the distance between the electrode plates to the surface area of the plate.

• The molar conductivity of an electrolytic solution is the conductance of the volume of the solution containing a unit mole of electrolyte that is placed between two electrodes of unit area cross-section or at a distance of one-centimeter apart.
• The unit of molar conductivity is S⋅m²⋅mol^-1.

• The molar conductivity of an electrolytic solution is the conductance of the volume of the solution containing a unit mole of electrolyte that is placed between two electrodes of unit area cross-section or at a distance of one-centimeter apart.
  
  Where C = concentration of electrolyte

 
It is Debye-Huckle Onsager Equation.

•  Na⁺ has lower molar conductance than the ions that are greater in size than Na such as K+, Cs+ as the molar conductance is inversely proportional to the solvation of ions.
• Smaller the ion, the greater will be the solvation, and hence lower will be the molar conductance.

H⁺ ions will have the maximum molar conductivity amongst the given cations due to Grothus conduction.

Exceptionally high values are found for H⁺ (349.8 S·cm²/mol) and OH⁻ (198.6 S·cm²/mol), which are explained by the Grotthuss proton-hopping mechanism for the movement of these ions.

• Equivalent conductivity (Λ_eq) measures conductivity per equivalent of solute, while molar conductivity (Λ_m) measures conductivity per mole of solute.
• Fe₂(SO₄)₃ dissociates into 2 Fe³⁺ ions and 3 SO₄^2- ions, yielding 6 equivalents per mole (2 x 3 + 3 x 2).
• The relationship is:Λ_eq = Λ_m / Number of Equivalents per Mole
• For Fe₂(SO₄)₃, Λ_eq=Λ_m/6.

According to kholaraus law,
NH₄OH = NH₄ + OH
i.e. NH₄ + Cl + Na + OH – Na – Cl = NH₄Cl + NaOH - NaCl

Molar conductivity is defined as the conductivity of an electrolyte solution divided by the molar concentration of electrolyte.

∧_m = (k × 1000)/M

= 1/x × 1000/y

= 1000/xy

• Smaller the ion, the greater will be the solvation, and hence lower will be the molar conductance.

• The Debye-Huckel was proposed by Peter Debye and Erich Huckel as a theoretical explanation for departure from ideality in solutions of electrolytes, further modified by Lars Onsager in 1927.
• Onsager was able to derive a theoretical expression to account for the empirical relation known as Kohlrausch's law for the molar conductivity,
  Am = Am_o - K(c)^½

For stronger electrolytes:
A_m = A_m^o - (A + BAm_o)(c)^1/2ac

The influence of ion-ion interactions on the conductivity of strong electrolytes was studied by Debye and Huckel.
They considered that each ion is surrounded by an ionic atmosphere of opposite sign, and derived an expression relating the molar conductance of strong electrolytes with the concentration by assuming complete dissociations.
It was further developed by Onsager. For a uni-univalent electrolyte the Debye Huckel and Onsager equation is given below.

Where A and B are constants which depend only in the nature of the solvent and temperature.

• Because t_H⁺ has a maximum value of transference no. as compared to other cations.
• Hence, t_Cl^- will be minimum in 0.1 M HCl solution.