Question

I still don't get this problem!

Toxic chemicals in drinking water usually are reported and a safety level specified in units of parts per million (ppm) by mass. What is the molar concentration of arsenic in a water sample that has 1ppm arsenic (As)?

My teacher's work:

(1g As/1x10^6 g soln) x (1 mol As/74.92 g As) x (1 g soln/mL) x (1.0 x10^3 mL/1L)= 1x10^-5 mol As/L soln

Where did the 1 g As/1x10^6 g soln and 1g soln/1mL come from?

Answer 1

One ppm is one millionth of a gram or in simpler terms, 10^6.