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Molarity

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.

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Molarity

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  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.

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