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Concentration of Solutions. Concentration of Solutions. Measure of the amount of solute per amount of solvent Dilute – solution with small amount of solute Concentrated – solution with large amount of solute. Percent by Mass. _mass of solute_ X 100 = % mass of solution
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Concentration of Solutions • Measure of the amount of solute per amount of solvent • Dilute – solution with small amount of solute • Concentrated – solution with large amount of solute
Percent by Mass _mass of solute_ X 100 = % mass of solution _part X 100 = % whole remember: part + part = whole solute + solvent = solution Example: A solution contains 54.5 g NaCl in 145.5 g water. What is the percent NaCl by mass? 54.5 g NaCl = 54.5 g NaCl + 145.5 g H2O 54.5 g NaCl X 100 = 200.0 g solution 27.3%
Molarity molarity (designated by M) = molar concentration = moles of solute liter of solution Examples: What is the molarity of a solution that contains 90.0 g NaCl in 3.50 liters of solution? 90.0 g NaCl X 1 mol NaCl = 58.5 g NaCl 1.54 mol NaCl = 3.50 liters solution 0.440M You have 0.8 L of a 0.5 M HCl solution. How many moles of HCl does this solution contain? M = mols rearrange the equation and liter mols = Molarity X liters mols = 0.5 M X 0.8 L = 0.4 mols HCl
Molality molality (designated by m) = molal concentration = moles solute kg of solvent for water 1 mL = 1 g because density of H2O = 1 g/mL Examples: What is the molality of a solution that contains 165.0 g NaCl in 2 liters of water? 2 liters of water = 2000 mL of water = 2000 g water = 2 kg 165.0 g NaCl X 1 mol NaCl = 58.5 g NaCl 2.821 mol NaCl = 2 kg 1.411 m How much iodine must be added to prepare a 0.48 m solution of iodine in CCl4 if 100.0 g of CCl4 is used? molality = mol solute rearrange and kg solvent mols iodine = molality X kg solvent = 0.48 m X .1000 kg CCl4 = 0.048 mol iodine change mols iodine to grams 0.048 mol I2 X 253.8 g I2 = 1 mol I2 12.2 g I2