Advertisements
Advertisements
Question
Answer the following:
What is Kohlrausch law of independent migration of ions? How is it useful in obtaining molar conductivity at zero concentration of a weak electrolyte? Explain with an example.
Advertisements
Solution
1) Kohlrausch law states that “at infinite dilution each ion migrates independent of co-ion and contributes to total molar conductivity of an electrolyte irrespective of the nature of other ions to which it is associated.”
2) Both cation and anion contribute to molar conductivity of the electrolyte at zero concentration and thus ∧0 is the sum of molar conductivity of cation and that of the anion at zero concentration.
Thus, Λ0 `= "n"_+lambda_+^0 + "n"_(_) lambda_(-)^0`
where λ+ and λ_ are molar conductivities of cation and anion, respectively, n+ and n– are the number of moles of cation and anion specified in the chemical formula of the electrolyte.
3) Determination of molar conductivity of weak electrolyte at zero concentration:
The theory is particularly useful in calculating ∧0 values of weak electrolytes from those of strong electrolytes.
For example, ∧0 of acetic acid can be calculated by knowing those of HCl, NaCl and CH3COONa as described below:
Λ0 (HCl) + Λ0 (CH3COONa) - Λ0 (NaCl)
`= lambda_("H"^+)^0 + lambda_("Cl"^-)^0 + lambda_("CH"_3"COO"^-)^0 + lambda_("Na"^+)^0 - lambda_("Na"^+)^0 - lambda_("Cl"^-)^0`
`= lambda_("H"^+)^0 + lambda_("CH"_3"COO"_-)^0` = Λ0 (CH3COONa)
Thus, Λ0 (CH3COONa) = Λ0 (HCl) + Λ0 (CH3COONa) - Λ0 (NaCl).
Because Λ0 values of strong electrolytes, HCl, CH3COONa and NaCl, can be determined by extrapolation method, the Λ0 of acetic acid can be obtained.
APPEARS IN
RELATED QUESTIONS
0.05 M NaOH solution offered a resistance of 31.6 Ω in a conductivity cell at 298 K. If the cell constant of the cell is 0.367 cm-1, calculate the molar conductivity of NaOH solution.
The molar conductivity of 0.05 M BaCl2 solution at 25° C is 223Ω-1 cm2 mol-1. What is its conductivity?
Choose the most correct option.
Two solutions have the ratio of their concentrations 0.4 and ratio of their conductivities 0.216. The ratio of their molar conductivities will be ______.
What is a cell constant? What are its units? How is it determined experimentally?
Answer the following in one or two sentences.
Write the relationship between conductivity and molar conductivity and hence unit of molar conductivity.
Answer the following in brief.
Explain the effect of dilution of the solution on conductivity.
Kohlrausch law is applicable for the solution _______.
SI unit of conductivity is _______.
Write applications of Kohlrausch’s Law.
Write three important steps required to determine molar conductivity.
Calculate molar conductivities at zero concentration for CaCl2 and NaCl.
Given: molar ionic conductivities of Ca2+, Cl–, Na+ ions are respectively, 104, 76.4, 50.1 Ω–1 cm–2 mol–1
If resistivity of 0.8 M KCI solution is 2.5 × 10-3 Ω cm. Calculate molar conductivity of solution?
Conductivity of KCI solution is 0.0027 Ω−1 m−1 at 25°C. The resistance of the solution is 82.4 Ω. The cell constant is ____________ m−1.
The molar conductivities at zero concentration for Ca2+ and CaCl2 are 104 and 256.8 Ω−1 cm2 mol−1 respectively. The molar conductivity at zero concentration for Cl− is ____________.
The resistance of a conductivity cell containing 0.001 M KCl solution at 298 K is 1500 Ω. What is the cell constant if conductivity of 0.001 M KCI solution at 298 K is 0.146 × 10−3 S cm−1?
What is the relation between cell constant, conductivity and electrical resistance?
Conductivity of a conductor is ____________.
What is the value of cell constant if conductance and conductivity of a solution is same?
What will be the concentration of NaCl solution, if the molar conductivity and conductivity of NaCl solution is 124.3 Ω-1 cm2 mol-1 and 1.243 × 10-4 Ω-1 cm2 respectively?
A conductivity cell dipped in 0.5 M KCl gives a resistance of 250 ohms. If the conductivity of KC I solution is 6.68 × 10-3 S cm-1, what is the cell constant?
If the resistivity of 0.1 M KCI solution is 50 Ω cm, what is it's molar conductivity?
Which of the following has least conductivity in aqueous solution?
Calculate molar conductivity for 0.5 M BaCl2 if its conductivity at 298K is 0.01 Ω–1 cm–1.
A conductivity cell filled with 0.02 M AgNO3 gives at 25°C resistance of 947 ohms. If the cell constant is 2.3 cm-1, what is the molar conductivity of 0.02 M AgNO3 at 25°C?
What is the SI unit of molar conductivity?
Define the term cell constant.
When electric current is passed through acidified water, 112 mL of hydrogen gas at STP collected at the cathode in 965 seconds. The current passed in amperes is ______.
Two solutions have the ratio of their concentrations 0.4 and ratio of their conductivities 0.216. What is the ratio of their molar conductivities?
