Topic 9 The Mole
III. Molarity
A. Molarity
• Concentration of a solution.
substance being dissolved
moles of solute
Molarity (M) 
liters of solution
total combined volume
A. Molarity
2M HCl
What does this mean?
You would read this as
Hydrochloric acid with a
Molarity of 2.
mol
M
L
2 mol HCl
2M HCl 
1L
Conversion Factors:
We are really just adding one more of them.
molar mass
(g/mol)
6.02  1023
(particles/mol)
MASS
IN
NUMBER
MOLES
OF
GRAMS
PARTICLES
Molarity (mol/L)
Aqueous solution
LITERS
OF
SOLUTION
• Ex 1). What is the molarity of a solution
containing 0.32 moles of NaCl in 3.4
liters?
• molarity =0.32 moles NaCl
3.4 L
•
=0.094 M NaCl
• Ex 2). Find the molarity of a 250 mL
solution containing 10.0 g of NaF.
10.0 g
mol
M
L
M=
1 mol
41.99 g
0.238 mol
0.25 L
= 0.238 mol NaF
= 0.95M NaF
• Ex 3). How many grams of NaCl are
required to make 0.500L of 0.25M
NaCl?
0.500 L
0.25 mol 58.44 g
1L
0.25 mol
0.25M 
1L
1 mol
= 7.3 g NaCl
• How would you prepare 400. ml of 1.20 M
solution of sodium chloride?
•
•
Remember:1.20 M NaCl =1.20 moles NaCl
1.00 L solution0.400 L solution x1.20 moles NaCl
1.00 L solution=0.480 moles NaCl0.480 moles NaCl x58.5 g NaCl
1 mole NaCl=28.1 g NaCl
Dissolve 28.1 g NaCl in enough water to make 400 mL of solution.