Question

A solution is found to be 0.0404% by weight CoBr₃. What is the concentration of the Br^1- ion expressed in ppm?

Answer 1

Atomic mass Co = 58.93
Atomic mass 3 Br = 3 x 79.90 = 239.7

Total = 298.6

0.0404% by weight means, 0.0404 g of CoBr3 in 100g of solution

Hence, from the molecular formula and molar mass,

         298.6 g of CoBr3 --- 239.7 g of Br is present

So,    0.0404 g of CoBr3 ---- > (0.0404 * 239.7) / 298.6 = 0.0324 g of Br

Therefore, 100g of solution contains 0.0324g of Br

                             = 0.0324 g / 100 g of solution

                             = 0.000324 g/ g of solution

Hence in ppm it must be,
                             = 0.000324 * 10^6 ug /g

                              = 324 ppm