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

Question

Mateo Aguilar · Accepted Answer

#"2.25 g KCl"#

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.

Ellie Andrews · Answer

undefined To find the mass of potassium chloride in the solution, you can use the percent by mass formula:

Mass of solute = Percent by mass × Mass of solution

First, convert the percent to a decimal by dividing by 100:

5.00% = 5.00/100 = 0.0500

Then, multiply the mass of the solution by the percent by mass:

Mass of solute = 0.0500 × 45.0 g = 2.25 g

So, there are 2.25 grams of potassium chloride in 45.0 grams of a 5.00% solution.