# 16.2 Concentration of Solutions

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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

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

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

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

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

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

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

Percent Solutions

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

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: %

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)