Question

calculate the mean ionic activity of a 0.0350 m Na3PO4 solution for which the mean activity coeffiecient is 0.685.

Answer should be: 0.0547

Please show me how to get there. Thank you

Answer 1

Answer – We are given molality of Na₃PO₄ = 0.0350 m

The mean activity coeffiecient , γ_+/- = 0.685

We know, there are 4 ions in the Na₃PO₄, 3 for Na⁺ and 1 for PO₄^3- and we know formula for m+/-

So, m_+/- = (m₊ *m_-)^1/4* m

               = (3³ * 1¹)^1/4 * 0.0350 m

               = 0.0798

We know, ionic activity, a_+/- = γ_+/- * m_+/-

                                              = 0.685 * 0.0798

                                               = 0.0547