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16.2 Concentration of Solutions

16.2 Concentration of Solutions. Learning Objectives. Solve problems involving the molarity of a solution Understand dilution and how to do dilution calculations Define and calculate percent by volume and percent by mass solutions. Molarity ( M ).

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16.2 Concentration of Solutions

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  1. 16.2 Concentration of Solutions Learning Objectives • Solve problems involving the molarity of a solution • Understand dilution and how to do dilution calculations • Define and calculate percent by volume and percent by mass solutions

  2. Molarity (M) • Molarity (M) is the most common form of expressing solution concentration • Based on the total solution volume

  3. If someone tells you that you have a 5.0 M solution you can assume this: 5 moles solute 1 liter solution Molarity assumption

  4. Example of Molarity (M) calculation Calculate the molarity of a solution that contains 5.8g KCl in 550mL of solution. Solution: 5.8g KCl x 1 mol KCl = 0.078 mol KCl 74.55g KCl 0.078 mol KCl = 0.55 L solution Answer: 0.14M

  5. Making Dilutions • Most solutions are stored as concentrated stock solutions • Fresh solution made using dilution

  6. Moles of solute before dilution (i) Moles of solute after dilution (f) = Dilution Add Solvent = MfVf MiVi Visualizing a Dilution

  7. Dilution Calculation Stock Solution M1V1 = M2V2 Solve for V1 V1= M2V2 M 1 V1=(0.400M)(100.0mL) (2.00M) V1= 20.0 mL (so 20.0 mL of stock solution will be measured and diluted with 80.0 mL of water) How many mL of aqueous 2.00 M MgSO4 solution must be diluted with water to prepare 100.0 mL of aqueous 0.400 M MgSO4? M1= 2.00 M MgSO4 M2 = 0.400 M MgSO4 V2 = 100.0 mL of 0.400 M MgSO4 V1 = ?? mL of 2.00 M MgSO4 New Solution

  8. Percent Solutions

  9. % = mass solute x 100 mass solution Assumptions you can make: A 5.0% solution = 5g solute 100g solution Mass Percent

  10. Mass Percent Calculation What is the mass percent of 500g of water containing 6.50g of copper sulfate? Solution: 6.50 CuSO4x 100% = (500g +6.50g) solution Answer: 1.28 %

  11. Parts per Million (ppm) Parts per million (ppm) is a ratio of parts of a solute to one million parts of a solution. Usually it is used when describing amount of contaminants in water. What is the ppm of copper sulfate if you have a solution of 500g of water containing 6.50g of copper sulfate? Solution: 6.50 CuSO4x 106 =12833(12800 ppm) (500g + 6.50g)

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