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16.2 Concentration of Solutions 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 Learning Objectives

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

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

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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 = mol KCl 74.55g KCl mol KCl = 0.55 L solution Answer: 0.14M

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

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Dilution Add Solvent Moles of solute before dilution (i) Moles of solute after dilution (f) = MiViMiVi MfVfMfVf = Visualizing a Dilution

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Dilution Calculation How many mL of aqueous 2.00 M MgSO 4 solution must be diluted with water to prepare mL of aqueous M MgSO 4 ? M 1 = 2.00 M MgSO 4 M 2 = M MgSO 4 V 2 = mL of M MgSO 4 V 1 = ?? mL of 2.00 M MgSO 4 M 1 V 1 = M 2 V 2 Solve for V 1 V 1 = M 2 V 2 M 1 V 1 =(0.400M)(100.0mL) (2.00M) V 1 = 20.0 mL (so 20.0 mL of stock solution will be measured and diluted with 80.0 mL of water) Stock Solution New Solution

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Percent Solutions

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

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Mass Percent Calculation What is the mass percent of 500g of water containing 6.50g of copper sulfate? Solution: 6.50 CuSO 4 x 100% = (500g +6.50g) solution Answer: 1.28 %

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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 CuSO 4 x 10 6 =12833 (12800 ppm) (500g g)

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