Question

A pharmacist wants to make 18 ml of a 6% hydrogen peroxide solution. How many mls of 5% hydrogen peroxide must he mix with 7% hydrogen peroxide to make a 6% hydrogen peroxide solution?

Answer 1

These are so much fun! Let's start with a table, cuz that's the easiest thing to do here to keep track of the info. The first thing we are told is that the final amount needs to be 18 mL. So that 18 will go in the amount column in the final row. Next we need to consider that he wants this final solution to be 6% peroxide. Change that to a decimal (.06) and put it in the % peroxide column in the "final" row. Next we are told that solution A is 5% peroxide, so .05 in the % peroxide column in the "solution A" row, and that solution B is 7% peroxide. So change that to .07 and put it into the % peroxide column in the "solution B" row. The question they are asking is how much of each of the first solution and the second solution (I named them A and B) do we need to mix together to get a final solution of 18 mL that is 6% peroxide. So we need to add solution A and solution B together and set them to = the final. How do we do that without all the info, you ask? Well, if he wants a total of 18 mL, and we do not know either amounts of A or B, we can call the amount for solution A "x" and then the amount for solution B would be "18-x", right? Let's fill in our table, now.