how to answer

Question

A water bottle label indicates a concentration of 2.5 ppm of nitrates. Find the mass, in grams, of the nitrates in the 500 mL bottle of water.

Answer 1

Another way to write ppm is mg/liter.  Thus, 2.5 ppm = 2.5 mg/liter.

2.5 mg/liter x 0. 5 L = 1.25 mg

1.25 mg x 1 g/1000 mg = 0.00125 g or 1.25x10^-3 g