Molar Concentration (Molarity) of Solutions
Molarity – the number of moles of solute dissolved in 1 L
of solution
Concentration (molarity) = moles of solute
Volume of solution (L)
n
C= n
v
C v
Units are mol/L or M (‘molarity’)
-
-
Molarity is the most useful way to express
concentration
Molarity is related to the number of particles in solution
e.x. A solution contains 5.85 g of sodium chloride
dissolved in 5.00 x 103 mL of water. What is the
concentration of sodium chloride?
Given: volume of solution = 5.00 x 103 mL
convert to L = 5.00 x 103 mL x
1L
1000 mL
= 5.00 L
Given : mass of solute = 5.85 g
Find: Concentration in mol/L
So we must first find # of moles of solute
Use n = m
M
(# moles = mass of sample )
molar mass
Molar mass NaCl = 22.99 + 35.45
= 58.44 g/mol
n=m
Mx
n=
5.85 g
58.44 g/mol
n = 0.1001 mol
Now we can plug this into our molarity equation..
C= n
C = 0.1001 mol
5.00 L
V
C = 0.0200 mol/L
Therefore, [NaCl] in the solution is 0.0200 mol/L
e.x. A solution contains 6.00 g of sodium phosphate dissolved in
250.0 mL of distilled water.
a) Find the concentration of sodium phosphate
b) Find the concentration of sodium ions and phosphate ions
a) Na3PO4
Molar mass = 3(22.99) + 30.99 + 4(16.00)
= 163.94 g/mol
n= m
M
n = 6.00 g
163.94 g/mol
Find [Na3PO4]:
n = 0.036599 mol
C= n
v
C = 0.036599 mol
0.250 L
C = 0.146 mol/L
b) Find concentration of sodium and phosphate ions.
Na3PO4

3 Na+
[Na+] = 3 [Na3PO4]
= 3 (0.146 mol/L)
= 0.439 mol/L
+
PO4 3[PO4 3-] = [Na3PO4]
= 0.146 mol/L
Molar Concentration (Molarity) of Solutions
Molarity – the number of moles of solute dissolved in 1 L of solution
Concentration (molarity) =
moles of solute
Volume of solution (L)
n
C=
n
v
C
v
Units are mol/L or M (‘molarity’)
-
Molarity is the most useful way to express concentration
Molarity is related to the number of particles in solution
e.x. A student dissolves 5.85 g of sodium chloride in water to make a solution of
5.00 x 103 mL. What is the concentration of the solution in mol/L
e.x. A 250.0 mL solution contains 6.00 g of sodium phosphate dissolved in distilled
water.
a) Find the concentration of sodium phosphate in the solution
b) Find the concentration of sodium ions and phosphate ions
Read pages 313 – 316
# 19 -24 pg 316