Question

The molar conductivities of a divalent cation (M²⁺) and monovalent anion (A^-) are 57 S cm^-1 mol^-1 and 73 S cm^-1 mol^-1 respectively. Then find the total molar conductivity shown by their compound in S cm^-1 mol^-1

Answer 1

Correct Answer: 203

To find the total molar conductivity of the compound formed by M²⁺ and A^-, we need to use the formula for the molar conductivity of an electrolyte, which is the sum of the molar conductivities of its ions. For the compound M_xA_y, if z₊ and z_- are the charges of the cation and anion respectively, the formula is:

Λ_m = (x·λ_c + y·λ_a)

Given:

λ_c (M²⁺) = 57 S cm^-1 mol^-1

λ_a (A^-) = 73 S cm^-1 mol^-1

For compound MA₂:

Since M is divalent (M²⁺) and A is monovalent (A^-), the formula of the compound is MA₂.

Thus, for MA₂, x = 1 and y = 2.

Substituting values in formula:

Λ_m = 1(57) + 2(73)

= 57 + 146

= 203 S cm^-1 mol^-1

Verification:

The computed total molar conductivity is 203 S cm^-1 mol^-1. This value falls within the provided range (203,203).

Therefore, the total molar conductivity of the compound is 203 S cm^-1 mol^-1.