Question

19. A 250.0 mL aqueous solution contains 45.1 μg of a pesticide. Express the pesticide’s concentration in weight percent, in parts per million, and in parts per billion.

Answer 1

A 250.0 mL aqueous solution contains 45.1 μg of a pesticide. The pesticide’s concentration in weight percent, in parts per million, and in parts per billion can be expressed as follows:

Explanation:

Assuming density of water to be 1.00 g/mL

then:

                weight% = [mass solute (in g) / mass solution (in g)] X 100

                  mass% = (4.51X10^-5 g /250 g) X 100 = 1.80X10^-5 % (m/m)

                          parts per million = mg solute / kg solution

                          ppm = 0.0451 mg / 0.250 kg = 0.180 ppm

                            ppb = ug/kg = 45.1 / 0.250 = 180 ppb