The molar conductivity of 0.007 M acetic acid is 20 S cm2 mol⁻¹. What is the dissociation constant of acetic acid ? Choose the correct option.
Correct Answer :
1.75×10⁻⁵ mol L⁻¹
Solution :
The correct option is 1.75×10⁻⁵ mol L⁻¹.
Step-by-step Derivation:
1. Identify the given values:
Concentration of acetic acid,
Molar conductivity of acetic acid at concentration ,
Limiting molar conductivity of hydrogen ion,
Limiting molar conductivity of acetate ion,
2. Calculate the limiting molar conductivity of acetic acid ():
According to Kohlrausch's law of independent migration of ions:
3. Calculate the degree of dissociation ():
The degree of dissociation is the ratio of molar conductivity at concentration to the limiting molar conductivity:
4. Calculate the dissociation constant ():
For a weak acid like acetic acid, the dissociation constant is given by:
Since is very small compared to 1, we can approximate :
Substituting the values:
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