How many grams of potassium chloride are in 45.0 g of a 5.00% (by mass) solution?

1 Answer
Stefan V.
May 16, 2016

"2.25 g KCl"

Explanation:

A solution's percent concentration by mass, "% m/m", essentially tells you how many grams of solute, which in your case is potassium chloride, "KCl", you get per "100 g" of solution.

You're dealing with a "5.00% m/m" solution of potassium chloride, so right from the start you should be able to look at this solution and say that it contains "5.00 g" of solute for every "100 g" of solution.

So, if "100 g" of solution will contain "5.00 g" of solute, it follows that "45.0 g" of solution will contain

45.0 color(red)(cancel(color(black)("g solution"))) * overbrace("5.00 g KCl"/(100color(red)(cancel(color(black)("g solution")))))^(color(purple)("= 5.00% m/m")) = color(green)(|bar(ul(color(white)(a/a)"2.25 g"color(white)(a/a)|)))

The answer is rounded to three sig figs.

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