Concentration – amount of solute per quantity of solvent

Ways to express the concentration of a solution1. Concentration as a Mass/Volume Percent2. Concentration as a Mass/Mass Percent3. Concentration as a Volume/Volume Percent

Mass/Volume Percent

• Mass of solute dissolved in a volume of solution, expressed as a %

Mass/volume percent = x 100%

Example: Saline solution contains 0.9g of sodium chloride dissolved in 100 mL of solution or 0.9%

Mass of solute (in g)Volume of solution (in mL)

A pharmacist adds 2.00 mL of distilled water to 4.00g of a powdered drug. The final volume of the solution is 3.00 mL.

a. What is the percent (m/v) of the solution?

Mass/volume percent= x 100%

= x 100%

mass of solute (in g)Volume of solution (in mL)

4.00 g3.00 mL

= 133%

Use ratios or cross out units to solve for the mass of solute in 100 mL

=

x =

x 100 mL

4.00 g3.00 mL

4.00g x 100 mL 3.00 mL

b. What is the concentration of the drug in g/100 mL of solution?

133% means 133g/100 mL of solution

X = 4.00g x 100ml x 13.00ml

= 133 g

= 133 g

Many people use a solution of trisodium phosphate to clean walls before putting up wall paper. The recommended concentration is 1.7% (m.v). What mass of TSP is need to make 2.0 L

solution?

(m/v) percent = x 100%

rearrange the equation to solve for mass of solute

Mass of solute= =

Mass of solute (g)Volume of solution (in mL)

(m/v) percent x volume of solution 100%

1.7% x 2000 mL 100%

= 34 g

Concentration as a Mass/Mass percent

Mass/mass percent gives the mass of a solute divided by the mass of a solution

- also referred to as percent (m/m)

Mass/mass percent = x

100 % Mass of solute (in g)Mass of solution (in g)

Calcium chloride can be used instead of road salt to melt the ice on roads during the winter. To determine how much

calcium chloride had been used on a road, a student took a sample of slush to analyze. The sample had a mass of 23.47 g. When the solution was evaporated, the residue had a mass

of 4.58 g. What was the mass/mass percent of calcium chloride in the slush?

Mass/mass percent = x 100%

= x 100%

=The mass/mass percent was 19.5% (m/m)19.5 g of calcium chloride was dissolved in 100 g of

solution

Mass of solute (in g)Mass of solution (in g)

4.58 g23.47 g

19.5 %

Concentration as a Volume/Volume Percent

Volume/volume percent gives the volume of solute divided by the volume of solution

• Also referred to as percent (v/v), volume percent concentration

Volume/volume percent = x 100%

volume of solute (in mL)Volume of solution (in mL)

Rubbing alcohol is commonly used as an antiseptic for small cuts. It is sold as 70% (v/v)

solution of isopropyl alcohol in water. What volume of isopropyl alcohol is used to make 500

mL of rubbing alcohol?Using this equation,Volume/volume percent = x 100 %

Rearrange to solve for volume of solute:

Volume of solute = =

350 mL of isopropyl alcohol is used to make 500 mL of 70%

(v/v) rubbing alcohol.

volume of soluteVolume of solution

Volume/volume % x volume of solution 100%

70% x 500 mL 100%

= 350 mL

Concentration in parts per million or parts per billion

ppm – parts per million (106)(one part solute per million parts of solution)

ppb – parts per billion (109)(one part solute per billion parts of solution)

Usually mass/mass relationships ie. The mass of solute compared with the mass of solution.

ppm = x 106 OR

mass of solute (g)Mass of solution (g)

Mass of soluteMass of solution

x g 106 g of solution=

Mercury poisiong becomes apparent when a person build up more than 20.mg of Mercury in

their body. Express this amount as ppm for a 60.kg person

You must first convert everything into grams• 20mg/1000g = 2.0 x 10-2 g• 60kg x 1000g = 6.0 x 104 g

• Ppm = mass solute x 106

mass solution = 2.0 x 10-2 g x 106

6.0 x 104 g = (3.33 x 10-7g) x 106

= .33 ppm

Homework

• Pg 376 #21-30, pg 378 #31,39