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Concentration of Solutions. Spring Semester, 2013 Mrs. L. Fox. Concentration. The amount of a dissolved substance occupying a given volume of the solution. Dilute Solutions. Contain few solute molecules. Concentrated Solutions. Contain many solute molecules. Molarity.
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Concentration of Solutions Spring Semester, 2013 Mrs. L. Fox
Concentration • The amount of a dissolved substance occupying a given volume of the solution
Dilute Solutions • Contain few solute molecules
Concentrated Solutions • Contain many solute molecules
Molarity • The number of moles of solute dissolved in 1 liter of solution • Symbol is M • Units are mol/L • A solution that is 0.75 M KCl • Contains 0.75 mols of KCl in every liter
Make 1 liter of a 0.75 M solution of KCl • Calculate the molar mass of KCl • 1 mol K = 39.10 g/mol • 1 mol Cl = 35.45 g/mol • 1 mol KCl = 39.10 + 35.45 = 74.55 gKCl/mol
Convert the molarity to the sample mass required 0.75 M KCl = 0.75 molsKCl/L * 74.55 g/mol = 55.91 gKCl/L You need to add 55.91 g of KCl to 1 liter of water to make 0.75 M KCl solution
What if you want a smaller amount? To make 150 mL 55.91 g/L * 1 L/1000 mL * 150 mL = 8.39 gKCl
Molarity Calculations M = # mol solute/# L solution
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Diluting Stock Solutions • Sometimes, the molarity of a solution is not what you want • You have to dilute the solution to get the molarity you do want • For that, you use • M1V1 = M2V2 (In Chem Reference Sheet)
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