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**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

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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 0.078 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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**= Visualizing a Dilution = MiVi MfVf Dilution Moles of solute**

Add Solvent Moles of solute before dilution (i) after dilution (f) = MiVi MfVf =

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Dilution Calculation Stock Solution How many mL of aqueous 2.00 M MgSO4 solution must be diluted with water to prepare mL of aqueous M MgSO4? M1= 2.00 M MgSO4 M2 = M MgSO4 V2 = mL of M MgSO4 V1 = ?? mL of 2.00 M MgSO4 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) New Solution

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Percent Solutions

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**Assumptions you can make:**

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: CuSO4 x 100% = (500g +6.50g) solution Answer: %

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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: CuSO4 x 106 =12833(12800 ppm) (500g g)

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Making dilutions A lot of the time in chemistry, scientists need to make a dilution from a stock solution to use in reactions M 1 V 1 = M 2 V 2 Make sure.

Making dilutions A lot of the time in chemistry, scientists need to make a dilution from a stock solution to use in reactions M 1 V 1 = M 2 V 2 Make sure.

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