Solutions Quantitative Expressions of Concentration Percent by mass

Solutions

Quantitative Expressions of Concentration Percent by mass n Percent by volume n Molarity n Molality n Dilution of solutions n

Percent by Mass Percent by mass gives the mass of solute per mass units of solution n Percent solute=mass of solute x 100% mass of solution n n Mass of solution = mass of solute + mass of solvent

Percent by Mass Problems n n n Calculate the % by mass of a Na. Cl solution made by adding 50 g of Na. Cl to 100 m. L of water. Calculate the mass of Na. Cl contained in 200. g of a 6. 00% solution of Na. Cl A 6. 00% solution of Na. Cl contains 40. 0 g of Na. Cl. Calculate the mass of the solution.

Percent by Volume Percent by volume gives the volume of solute per volume units of solution n Percent solute=volume of solute x 100% volume of solution n n volume of solution = volume of solute + volume of solvent

Percent by Volume Problems What is the % by volume of a solution that is made by adding 25 m. L of acetone to 100 m. L of water? n A 6% solution of vinegar contains 3. 0 m. L of HC 2 H 3 O 2. Calculate the volume of water that was added. n

Molarity n Molarity-the moles of solute pervolume of solution in liters. M = molarity = moles of solute liters of solution (solution = solvent + solute)

Ø A solution of Na. Cl has a molarity of 1 (1 M). What does this mean? • • 1 mole of Na. Cl is dissolved in enough water to make 1 L. 1 mole = 58 g Na. Cl Ø A 1 M solution of Na. Cl contains 58 g of Na. Cl dissolved in 1 liter of water. • • • How much salt is dissolved in a 2 M solution? 116 g How much salt is dissolved in a 6 M solution? 348 g Which is more concentrated?

Molarity Problems Calculate the molarity of a solution prepared by dissolving 11. 5 g of solid Na. OH in enough water to make 1. 50 L of solution. n Calculate the mass of Ba(OH)2 required to prepare 2. 50 L of a 0. 0600 M solution of Ba(OH)2. n

Molality-the number of moles of solute per kilogram of solvent n Molality = moles of solute kilogram of solvent n

n n n n n A solution of Na. Cl contains 58 g of Na. Cl dissolved in 1 liter of water. The density of water is 1. 00 g/m. L. What is the molality of the solution? 1 liter = 1000 m. L = 1000 g = 1 kg 58 g = 1 mole Molality = 1 mole/1 kg = 1 m How much salt must be dissolved in 100 g of water in order to make a 2. 0 molal (m) solution? 100 g =. 1 kg 2. 0 = x/. 1 X =. 2 moles x 58 g = 11. 6 g Will molarity and molality for the same solution always be equal? Explain.

Molality Problems n A solution is prepared by mixing 1. 00 g of ethanol (C 2 H 5 OH) with 100. 0 g of water to give a final volume of 101 m. L. What is the molality?

Review What is the molarity? n What is the mass percent? n What is the % by volume? n What is the mole fraction? n

Dilution of Solutions Dilution occurs when more solvent is added to a solution without changing the amount of solute that is present. n M 1 V 1 = M 2 V 2 n For safety purposes when in a lab setting, concentrated solutions of acids and bases are always added slowly to water. n

Dilution Problems n How many m. L of 18. 0 M H 2 SO 4 are required to prepare 1. 00 L of a 0. 900 M solution of H 2 SO 4?