Expert: Scott A Wilson - 10/30/2009

Question
grace dilutes 4.8 fl. oz. of pure hydrogen peroxide with 27.2 floz. of water to make 32 fl oz of a bleaching solution. She then decides to replace a portion of the bleaching solution to create 32 fl. oz of a 22% solution. How much bleaching solution should be replaced by pure hydrogen peroxide?

Answer
What would happen if we added 1 oz of hydrogen peroxide, in theory only:

4.8 oz   hydrogen peroxide present, as given in the problem;
32 oz   total fluid present, which is 4.8 hydrogen peroxide + 27.2 water;
1 oz   gross amount of straight hydrogen peroxide added;
1 oz   amount of fluid taken away;
0.15 oz   amount of hydrogen peroxide taken away; which leads to
0.85 oz   net amount of straight hydrogen peroxide would be added for each 1 oz gross.

Now 22% hydrogen peroxide is 7.04 ounces, so we want to add 7.04-4.8 = 2.04.
Since only 0.85 of the added is kept in the tank, we really want to add 2.04/0.85 =
2.4 oz of hydrogen peroxide to be added.