SAT Subject Test Chemistry,10 edition

Solution: First we need to convert the amount of NaCl into mass:

PARTS PER MILLION

The parts per million (ppm) of a solution is equal to the grams of solute divided by 1,000,000 g of
solution.

Example: A  chemical    analysis    shows   that    there   are 2.2 mg  of  iron    in  a   500 g   sample  of  tap

water.  Convert this    to  parts   per million (ppm).

Solution: First we  need    to  convert the amount  of  iron    to  grams.

2.2 mg  ×   1   g/1000  mg  =   0.0022  g   Fe

Second, we  need    to  create  a   proportion  between the amount  of  iron    per 500 g   of

water   and the amount  of  iron    per 1,000,000   g   of  water.

Cross   multiply,   then    solve   for x.

The units   of  grams   cancel  out,    leaving us  with    units   of  parts   per million.