Molarity

1
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.

2
Molarity ProblemsYou 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

3
Molarity ProblemsYou 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.

4
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.

5
Preparing a solutionyour 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.