Question

Calculate the mass of unknown solid required to prepare 100 mL of a solution that is 100 ppm in Ca by assuming that the sample contains 50 wt% CaCO3. (Include units and use an appropriate number of sig figs.)

Answer 1

(1)

1 ppm = 1 mg/L

          = 1 mg/1000 mL

100 ppm = 100 mg/1000 mL

              = 10 mg/100 mL

Mass of Ca = 10 mg = 0.010 g

Mass of CaCO3 = 100.09/40.08 x 0.010

                          = 0.025 g

Mass of sample = 100/50 x 0.025

Mass of sample = 0.05 g