CONCENTRATION: MOLES PER LITRE
The molarity of a solution is the number of moles of solute dissolved into 1 litre (1 dm 3) of solution
Molarity (mol/L) =
moles of solute (n)
Volume of solution (L)
Example 1: Calculate the molarity of a solution if 16.5 g of HCl(g) was dissolved into 1.50 L of water.
Given: m = 16.5 g
MM = 36.5 g/mol
n= m
MM
n=
16.5 g
36.5 g/mol
n = _________ mol
Given: n = 0.452 mol
V = 1.50 L
M=
n/V
M = _________mol
L
M = _____ M or _____ mol/L
Example 2: How would you prepare a 75 mL sample of a
1.4 M solution of sodium chloride?
Strategy: Find the number of moles of sodium chloride and from that value find the mass.
Given:
V = 75mL = 0.075L
M = 1.4 mol/L
n=MxV
n = ________mol/L x ________ L
n = _____ mol (you may carry an extra figure on your calculation)
Given: n = ______ mol
MM = ______g/mol NaCl
Na = 23.0 g/mol
Cl = 35.5 g/mol
g/mol
m = n x MM
m = ________ mol x ________ g/mol
m = _________ of NaCl
N.B.
1 cm3 = 1 mL of solution, 1 dm3 = 1 L of solution
When performing dilution calculations, remember the following formula: M1V1 = M2V2 , where M1 and V1 are
your initial molarity and volume, and where M2 and V2 are your final molarity and volume.
Textbook Problems: Pg. 316 # 19 – 24, P. 321 # 25 - 27