How do I find grams of solute in a volume of solution, given parts per million?

In 250 ml of solution, I have 44 ppm of copper, 11 parts per million of lead, 69 parts per million of tin. How do I convert these to grams/pounds? Karl

Pick out the target. I'll assume that you want grams of copper, of lead, and of tin in the 250 mL of solution.
List the given information, and connect it with the target. You know the total volume of the solution. Volume of solution can be converted into an amount of solute using concentration. Parts per million can always be expressed as g solute per 1000000 grams of solution. You don't know the density of your solution, but if it's a dilute aqueous solution you can assume that 1 mL of solution has a mass of about 1.0 g, because the density of pure water is about 1.0 g/mL. That allows you compute the g Cu in the solution as follows:

250 mL soln 1.0 g soln
1 mL soln 44 g Cu
1000000 g soln = 0.011 g Cu
Check the answer. You're expecting a very small amount of copper. If there are 0.011g Cu in 250 mL solution, that corresponds to a concentration of (0.011 g Cu/250 g solution) × 10⁶ = 44 ppm Cu. Voila!

Author: Fred Senese senese@antoine.frostburg.edu

General Chemistry Online! How do I find grams of solute in a volume of solution, given parts per million?