What is percent concentration?

Aug 20, 2014

There are two types of percent concentration: percent by mass and percent by volume.

PERCENT BY MASS

Percent by mass (m/m) is the mass of solute divided by the total mass of the solution, multiplied by 100 %.

Percent by mass = $\text{mass of solute"/"total mass of solution}$ × 100 %

Example

What is the percent by mass of a solution that contains 26.5 g of glucose in 500 g of solution?

Solution

Percent by mass =

"mass of glucose"/"total mass of solution" × 100 % = (26.5"g")/(500"g") × 100 % = 5.30 %

PERCENT BY VOLUME

Percent by volume (v/v) is the volume of solute divided by the total volume of the solution, multiplied by 100 %.

Percent by volume = $\text{volume of solute"/"total volume of solution}$ × 100 %

Example

How would you prepare 250 mL of 70 % (v/v) of rubbing alcohol

Solution

70 % = "volume of rubbing alcohol"/"total volume of solution" × 100 % × 100 %

So

Volume of rubbing alcohol = volume of solution × $\text{70 %"/"100 %}$ = 250 mL × $\frac{70}{100}$

= 175 mL

You would add enough water to 175 mL of rubbing alcohol to make a total of 250 mL of solution.