Question

how many grams of KI are in 25.0ml of a 3.0%(m/v) KI solution?

Answer 1

Explanation:

Notice that you were given the solution's mass by volume percent concentration, which is defined as mass of solute divided by volume of solution, and multiplied by

100

.

In your case, a

3.0% w/v

potassium iodide solution will contain

3.0 g

of potassium iodide for every

100 mL

of solution.

You know that the volume of the sample is four times smaller than this value, so you can say right from the start that it will contain four times less potassium iodide.

25.0

mL solution

⋅

3.0 g KI

100

mL solution

=

0.75 g KI

The answer is rounded to two sig figs, the number of sig figs you have for the given concentration.