Question

The equivalent conductances of sodium chloride, hydrochloric acid and sodium acetate at infinite dilution are `126.45, 426.16` and `91.0ohm^(-1) cm^(-1)"equiv"^(-1)`, respectively, at `25^(@)C`. Calculate the equivalent conducatance of acetic acid at infinite dilution.
`Lambda_(m)^(0)(HCl)="426.16 S cm"^(2)mol^(-1)`
`Lambda_(m)^(0)(NaCl)="126.45 S cm"^(2)mol^(-1)`
`Lambda_(m)^(0)(CH_(3)COONa)="91 S cm"^(2)mol^(-1)`

Answer 1

According to Kohlraush s law,
`Lambda_(ooCH_(3)COONa)=lambda_(CH_(3)COO^(-))+lambda_(Na^(+))=91.0`.....(i)
`Lambda_(ooHCl)=lambda_(H^(+))+lambda_(Cl^(-))=426.16`.....(ii)
`Lambda_(ooNaCl)=lambda_(Na^(+))+lambda_(Cl^(-))=126.45`.....(iii)
Adding eqns. (i) and (ii) and subtracting (iii),
`lambda_(CH3COO^(-))+lambda_(Na^(+))+lambda_(H^(+))+lambda_(Cl^(-))-lambda_(Na^(+))-lambda_(Cl^(-))`
`=91.0+426.16-126.45`
`lambda_(CH3COO^(-))+lambda_(H^(+))=Lambda_(ooCH_(3)COOH)`
`="390.7 ohm"^(-1)cm^(2)"equiv"^(-1)`