Molarity
Concentration Based on Mass
Concentration - amount of solute
dissolved in a given amount of
solution
 Concentration of a solution has an
effect on


Physical properties
 Melting

and boiling points
Chemical properties
 Solution
reactivity
Moles and Equivalents
Chemical equations represent the
relative number of moles of
reactants producing products
 Many chemical reactions occur in
solution where it is most useful to
represent concentrations on a
molar basis

Molarity
The most common mole-based
concentration unit is molarity
 Molarity

Symbolized M
 Defined as the number of moles of solute
per liter of solution

moles solute
M
L solution
Molarity
2M HCl What does this mean?
mol
M
L
2 mol HCl
2M HCl 
1L
Molarity Calculations
molar mass
MASS
IN
6.02  1023
(particles/mol)
(g/mol)
NUMBER
MOLES
OF
GRAMS
PARTICLES
Molarity
(mol/L)
LITERS
OF
SOLUTION
Calculating Molarity from
Moles
Calculate the molarity of 2.0 L of
solution containing 5.0 mol NaOH
moles solute
 Use the equation

M

Substitute into the equation:
MNaOH = 5.0 mol solute
2.0 L solution
= 2.5 M
L solution
Molarity Calculations
 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
Molarity Calculations
 Find
the molarity of a 250 mL
solution containing 10.0 g of NaF.
10.0 g 1 mol
mol
M
L
M=
41.99 g
0.238 mol
0.25 L
= 0.238 mol NaF
= 0.95M NaF
Molar Volume of a Gas
Molar volume - the volume occupied
by 1 mol of any gas
 STP – Standard Temperature and
Pressure

T = 273 K (or 0oC)
 P = 1 atm


At STP the molar volume of any gas
is 22.4 L

Vgas = molesgas x (22.4L/1 mol)
Molar Mass and Density


A gas’s density will determine if it will sink or
float in the air
Molar mass = density x molar volume

At STP
grams grams 22.4 L

x
mole
L
1 mole