Unit 8: Solutions
Molarity
Concentration
 Concentration is a value that represents the
amount of solute dissolved in a solvent.
Concentrated solutions have a large amount of solute
relative to the solvent
Dilute solutions have a small amount of solute relative
to the solvent
 Concentration can be measured in Molarity,
%solution, ppm (parts per million)
Molarity
Molarity is the moles of solute per liter of
solution.
Note the volume is the total solution volume,
not the volume of solvent alone.
M = moles
Liters
= mass/molar mass
Liters
This is the most common way chemists
measure concentration
How it is made…
2 Molar Solution of NaCl
requires 2 moles of NaCl to be dissolved to
make 1L of solution
2 moles of salt (or 117 grams) are dissolved in 1L of
water to make a 2M NaCl(aq) solution
Practice Problem #1
 What is the molarity of HCl if 28g HCl is
dissolved in 500.mL of solution?
 mass=28.g
molar mass of HCl= 36.46g/mol
V= 500mL=0.500L (divide by 1000)
M= moles = (mass/molar mass)
Liter
Liter
=
(28/36.46)moles
0.500L
= 1.5 M
Practice Problem #2
 How many grams of sodium nitrate (NaNO3 ) are needed
to make 2 liters of a 0.100M solution?
M=0.100M
m=?
0.100M = (m/85)mols
2L
(0.100M)(2L)(85)= m
m=17g NaNO3
mm NaNO3 = 85g/mol
Solving using Dimensional Analysis
Molarity can be used as a conversion
factor.
2.0 L
0.100moles
1 Liter
85 grams = 17g
1 moles
Example 3
 What is the molarity of a solution with 10.0
grams of AgNO3 is dissolved in 500.mls of
solution.
Molarity = Mass / Molar Mass
Liters of Solution
Must convert to
Liters!!
500mls/ 1000
M = 10.0g / 169.88 g/mol
0.500 Liters
M = 0.118 Molar
= 0.500 Liters
Example 4
How many grams of KNO3 should be used to
prepare 2.00 Liters of a 0.500M solution?
Molarity = Mass / Molar Mass
Liters of Solution
0.500 = mass / 101.11
2.0
(0.500)(2.0) =
Mass
101.11
Mass = (0.500)(2.0)(101.11)
Mass = 101.11 grams
Example 5
To what volume should 5.0grams of
KCl be diluted to in order to prepare a
0.25M solution?
Molarity = Mass / Molar Mass
Liters of Solution
0.25 = 5.0 / 74.55
Volume
V(0.25) = 5.0/74.55
V = 0.0671
0.25
V= 0.268 Liters =
268 mLs