Molarity
Unit of Concentration
There are many units of concentration
Molarity is most useful to the chemist
M = moles of solute
Liters of solution
Liters of solution means the total volume of
water and solute.
If I want a liter of solution I will not use a liter
of water.
Molarity Problems
You work them.
A saline solution contains 0.90 g NaCl in
exactly 100 ml of solution. What is the
molarity of the solution?
Convert g to moles
0.90g NaCl 1 mol NaCl
58.5 g NaCl
= 0.015 mol NaCl
Take 0.015 moles/ .100 L
Answer - 0.15 mol/L or 0.15 M NaCl
Molarity Problems
You work them.
How many moles of solute are present 1.5 L
of 0.24 M Na2SO4?
0.24 M = x mol
solve for x

1.5 L
Answer - 0.36 mol of Na2SO4
What if I asked you to find how many grams
of solute are present in the previous problem.
Convert your moles to grams.
Preparing a solution
How would you make 500.0 ml a 0.25 M
solution of copper (II) chloride?
0.25 M = mol/0.5000 L - change ml to liters
and solve for moles.
You need 0.13 moles of CuCl2. Converting to
grams equals 17 grams.
Final answer
Take 17 grams of CuCl2 and dissolve in enough
water to make 500.0 ml of solution.
Dissolve the 17 grams in say 400 ml of water.
Once the CuCl2 is dissolved add water up to
500.0 ml.
Preparing a solution
your turn
How would you prepare a solution of 0.40 M
KCl? If a volume is not given assume 1 L.
0.40 M = mol/ 1 L
mol = 0.40 mol needed
0.40 mol 74.6 g KCl
=
3.0x101 grams KCl
1 mol KCl
Take 3.0x101 grams of KCl and dissolve in
enough water to make a liter of solution.