# How many grams of #"KNO"_3# should be dissolved in water to make #"500.0 g"# of a #"20.0-ppm"# solution?

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1) 1.00 x 10^-3 g

2) 1.00 x 10^-4 g

3) 1.00 x 10^-1 g

4) 1.00 x 10^-2 g

1) 1.00 x 10^-3 g

2) 1.00 x 10^-4 g

3) 1.00 x 10^-1 g

4) 1.00 x 10^-2 g

##### 1 Answer

#### Explanation:

As you know, a solution's concentration in **parts per million** tells you the number of grams of solute present for every

#10^6 = 1,000,000#

grams of the solution. In your case, the target solution must have a concentration of

This means that the mass of potassium nitrate needed to make this solution is equal to

#500.0 color(red)(cancel(color(black)("g solution"))) * "20.0 g KNO"_3/(10^6color(red)(cancel(color(black)("g solution")))) = color(darkgreen)(ul(color(black)(1.00 * 10^(-2) quad "g")))#

The answer is rounded to three **sig figs**.

So, if you dissolve