Question

What mass of solution containing 5.00% potassium iodide, `KI`, by mass contains 258 mg `KI`?

Answer 1

`"5160 mg"`

Explanation:

Your goal here is to figure out the mass of your `"5.00% m/m"` potassium iodide solution that contains `"258 mg"` of potassium iodide, which is your solute.

As you know, a solution's percent concentration by mass, `"% m/m"`, is calculated by taking the number of parts of solute you get per `100` parts of solution.

In this case, you can say that a `"5.00% m/m"` potassium iodide solution contains `"5.00 mg"` of potassium iodide for every `"100 mg"` of solution.

You can thus use the solution's percent concentration as a conversion factor to figure out how many milligrams of solution would contain `"258 mg"` of solute

`258 color(red)(cancel(color(black)("mg KI"))) * "100 mg solution"/(5.00color(red)(cancel(color(black)("mg KI")))) = color(green)(|bar(ul(color(white)(a/a)color(black)("5160 mg solution")color(white)(a/a)|)))`

The answer is rounded to three sig figs.