1. 8.3 Concentration of solutions

2. Concentration – amount of solute per quantity of solvent
Ways to express the concentration of a solution
Concentration as a Mass/Volume Percent
Concentration as a Mass/Mass Percent
Concentration as a Volume/Volume Percent
Parts per million/billion
Molar Concentration

3. 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)

4. Mass of solute (in g) Mass/mass percent = x 100%
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 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 of solute (in g)
Mass of solution (in g)
Mass/mass percent = x 100%
= x 100% =
4.58 g
23.47 g
19.5 %
The mass/mass percent was 19.5% (m/m)
19.5 g of calcium chloride was dissolved in 100 g of solution

5. Molar Concentration

6. Molarity is the number of moles of solute that can dissolve in 1 L of solution.
Molar concentration (mol/L) =
Amount of solute (mol)
Volume of solution (L) n
C = V

7. Step 1: Find the number of moles of calcium chloride using n=m/M n= =
What is the concentration, in mol/L, of a solution formed by dissolving 28.0g of calcium chloride in enough water to make 225 mL of solution?
Step 1: Find the number of moles of calcium chloride using n=m/M n= = m M
= mol CaCl2
28.0
110.98

8. Step 2: Use c=n/V to calculate the molar concentration c= =
Notice the volume
has been converted from mL
to L
0.252
0.225 L
= 1.12 mol/L

9. How many grams of sodium nitrate would be needed to make 425 mL of 6
How many grams of sodium nitrate would be needed to make 425 mL of 6.00 mol/L solution?
Step 1: Find the number of moles using n= cV
n= (6.00 mol/L)(0.425L)
= 2.55 mol of sodium nitrate
Step 2: Calculate how many grams is needed using m = nM
m = (2.55 mol) (85.00 g/mol)
= 217 g of NaNO3

10. What final solution volume would be required to prepare
A mol/L solution of AgNO3(aq) if 1.20 g of the solid salt will be used?
MMAgNO3 = g/mol
C = mol/L
mAgNO3 = 1.20 g
V = ?
nAgNO3 = m/MM
= 1.20 g
169.9g/mol
= mol
V = n/C = mol/0.100 mol/L = L

11. 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)

12. What is the percent (m/v) of the solution?
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.
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 g
3.00 mL
= 133%

13. b. What is the concentration of the drug in g/100 mL of solution?
133% means 133g/100 mL of solution
Use ratios or cross out units to solve for the mass of solute in 100 mL x
100 mL
4.00 g
3.00 mL =
x =
X =
4.00g x 100ml x 1
3.00ml
4.00g x 100 mL
3.00 mL
= 133 g
= 133 g

14. Volume of solution (in mL) (m/v) percent = x 100%
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?
Mass of solute (g)
Volume of solution (in mL)
(m/v) percent = x 100%
Rearrange the equation to solve for mass of solute
Mass of solute= =
(m/v) percent x volume of solution
100%
1.7% x 2000 mL
100%
= 34 g

15. 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)

16. Volume/volume % x volume of solution 100%
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 = =
volume of solute
Volume of solution
Volume/volume % x volume of solution
100%
70% x 500 mL
100%
= 350 mL
350 mL of isopropyl alcohol is used to make 500 mL of 70% (v/v) rubbing alcohol.

17. 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 solute
Mass of solution
x g
106 g of solution =

18. A bottle of natural water contains 22 ppm of dissolved potassium ions
A bottle of natural water contains 22 ppm of dissolved potassium ions. How many atoms of potassium are contained in a 500 mL bottle of the water? Assume the density of the solution is g/mL)

19. The Maximum Acceptable Concentration (MAC) for lead in Canadian drinking water is mg/L. What is this concentration expressed in parts per million? (Assume the density of the solution is g/mL)

20. Mercury is a toxic compound
Mercury is a toxic compound. Calculate the parts per billion (ppb) of mercury in a 100g water sample that contains 0.98mg of mercury.