Search for Answers to Your Chemistry Questions

calculating parts per million

Most community water supplies have 0.5 ppm of chlorine added for purification. What mass of chlorine must be added to 100.0 L of water to achieve this level?

i really need help with this question i dont understand how to do it because it is completely different from the example in my book!!!

The formula for parts per million is

        ppm = mass of solute / mass of solution  x  1,000,000
In this case you are told that you have a 100.0 L of water (the solution).  Since the solution is essentially water, the density of the solution is very, very close to 1.00 g/ml.
And 100.0 L is equivalent to 100,000 mL.  If we use the density, we can find the mass of the solution:
                        100,000 mL  x  1.00 g/ml = 100,000 g

Now plug what we know into the equation for parts per million:

                          .5 ppm =  x grams of solute / 100,000 g solution  x 1,000,000

Solving for x yields  x grams of solute =  .5 x 100,000/ 1,000,000
                            x grams of solute = .5 x .1 = .05 grams of solute (chlorine)

basically if you can separate the magnitude of your units by 1000000 you will have ppm