Transcript mass solute
16.2 Concentration of Solutions
Learning Objectives
Solve problems involving the molarity of a
solution
Understand dilution and how to do
dilution calculations
Define and calculate percent by volume
and percent by mass solutions
Molarity (M)
Molarity (M) is the most common form of
expressing solution concentration
Based on the total solution volume
moles of solute mol
M
liters of solution
L
Molarity assumption
If someone tells you that you
have a 5.0 M solution you
can assume this:
5 moles solute
1 liter solution
Example of Molarity (M) calculation
Calculate the molarity of a solution that contains 5.8g KCl
in 550mL of solution.
Solution: 5.8g KCl x 1 mol KCl = 0.078 mol KCl
74.55g KCl
0.078 mol KCl =
0.55 L solution
Answer: 0.14M
Making Dilutions
Most solutions are stored as concentrated
stock solutions
Fresh solution made using dilution
M1V1 M 2V2
Visualizing a Dilution
Dilution
Add Solvent
Moles of solute
before dilution (i)
=
Moles of solute
after dilution (f)
MiVi
=
MfVf
Dilution Calculation
How many mL of aqueous 2.00 M
MgSO4 solution must be diluted
with water to prepare 100.0 mL
of aqueous 0.400 M MgSO4?
M1= 2.00 M MgSO4 New Solution
M2 = 0.400 M MgSO4
V2 = 100.0 mL of 0.400 M MgSO4
V1 = ?? mL of 2.00 M MgSO4
Stock Solution
M1V1 = M2V2
Solve for V1
V1= M2V2
M1
V1=(0.400M)(100.0mL)
(2.00M)
V1= 20.0 mL (so 20.0 mL of
stock solution will be
measured and diluted with
80.0 mL of water)
Percent Solutions
volsolute (mL)
% (v/v)
100
volsolution(mL)
mass solute (g)
% (m/v)
100
volsolution(mL)
mass solute (g)
% (m/m)
100
mass solution(g)
Mass Percent
% = mass solute x 100
mass solution
Assumptions you can make:
A 5.0% solution =
5g solute
100g solution
Mass Percent Calculation
What is the mass percent of 500g of water
containing 6.50g of copper sulfate?
Solution:
6.50 CuSO4 x 100% =
(500g +6.50g)
solution
Answer: 1.28 %
Parts per Million (ppm)
Parts per million (ppm) is a ratio of parts of a
solute to one million parts of a solution. Usually it
is used when describing amount of contaminants
in water.
What is the ppm of copper sulfate if you have a
solution of 500g of water containing 6.50g of
copper sulfate?
Solution:
6.50 CuSO4 x 106 =12833(12800 ppm)
(500g + 6.50g)