1. Molar Concentration Concentration
use the same formula, but express it in moles per liter instead of grams per liter
(past formula)
C = mass (g)
Volume (L)
C = n (moles)
Volume (L)

2. Concentration in moles per litre
C = mass (g)
Volume (L)
C = n (moles)
Volume (L)
C= g/L
C= mol/L
"MOLARITY"
RECALL
grams
moles
n (# of moles)= grams
molar mass

3. EXAMPLE # 1 STEP # 1 STEP # 2 SO...
If you need 4.0L of 0.2 mol/L of sodium chloride solution (NaCl), what mass of sodium chloride must you use?
STEP # 1
STEP # 2
Solve for the # of moles.
The questions asks for the answer in grams NOT moles……….
C = n (moles)
Volume (L)
SO...
n (# of moles)= grams
molar mass
5 L
.8mol= grams
58.5g/L
0.2mol/L = n(moles) 4
Na = 23 grams/mole
Cl = 35.5 grams/mole
58.5 grams/mole
n = 0.8 mole
g = 46.8 grams

4. EXAMPLE # 2
140 g of sodium hydroxide (NaOH) are dissolved in water to form 4 L of a solution.
WHAT IS THE MOLAR CONCENTRATION OF THIS SOLUTION?
STEP # 1
STEP # 2
Convert grams into moles
Next, use your formula to solve for concentration in moles per litre.
n (# of moles)= grams
molar mass
C = n (moles)
Volume (L)
Na = 23 grams/mole
O = 16 grams/mole
H = 1 gram/mole
40 grams/mole
5 L
n = 140g
40g/mol
C = 3.5 moles 4L
n = 3.5 moles
C = mole/L

5. KEY POINTS Be able to convert from grams to moles (or vice versa)
Know the formula for concentration in moles per litre
n (# of moles)= grams
molar mass
C = n (moles)
Volume (L)

6. PRACTICE PROBLEMS
WORKSHEET # 3