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.  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 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  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 Problems You work them.  How many moles of solute are present 1.5 L of 0.24 M Na 2 SO 4 ?  0.24 M = x molsolve for x  1.5 L  Answer - 0.36 mol of Na 2 SO 4  What if I asked you to find how many grams of solute are present in the previous problem.  Convert your moles to grams.  How many moles of solute are present 1.5 L of 0.24 M Na 2 SO 4 ?  0.24 M = x molsolve for x  1.5 L  Answer - 0.36 mol of Na 2 SO 4  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 CuCl 2. Converting to grams equals 17 grams.  Final answer  Take 17 grams of CuCl 2 and dissolve in enough water to make 500.0 ml of solution.  Dissolve the 17 grams in say 400 ml of water. Once the CuCl 2 is dissolved add water up to 500.0 ml.  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 CuCl 2. Converting to grams equals 17 grams.  Final answer  Take 17 grams of CuCl 2 and dissolve in enough water to make 500.0 ml of solution.  Dissolve the 17 grams in say 400 ml of water. Once the CuCl 2 is dissolved add water up to 500.0 ml.

5. 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 = 3.0x10 1 grams KCl 1 mol KCl Take 3.0x10 1 grams of KCl and dissolve in enough water to make a liter of solution.  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 = 3.0x10 1 grams KCl 1 mol KCl Take 3.0x10 1 grams of KCl and dissolve in enough water to make a liter of solution.