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Concentrations of Solutions 16.2 • Water must be tested continually to ensure that the concentrations of contaminants do not exceed established limits. These contaminants include metals, pesticides, bacteria, and even the by-products of water treatment. You will learn how solution concentrations are calculated. • (molarity; % v/v; %m/m; ppm)
16.2 Molarity • The concentration of a solution is a measure of the amount of solute that is dissolved in a given quantity of solvent. • A dilute solution is one that contains a small amount of solute. • A concentrated solution contains a large amount of solute.
16.2 Molarity • Molarity • How do you calculate the molarity of a solution?
16.2 Molarity • Molarity (M) is the number of moles of solute dissolved in one liter of solution. • To calculate the molarity of a solution, divide the moles of solute by the volume of the solution.
16.2 Molarity • To make a 0.5-molar (0.5M) solution, first add 0.5 mol of solute to a 1-L volumetric flask half filled with distilled water.
16.2 Molarity • Swirl the flask carefully to dissolve the solute. • Fill the flask with water exactly to the 1-L mark.
16.3 Sample Problem 16.3
16.2 Making Dilutions • Making Dilutions • What effect does dilution have on the total moles of solute in a solution? • Diluting a solution reduces the number of moles of solute per unit volume, but the total number of moles of solute in solution does not change.
16.2 Making Dilutions • The total number of moles of solute remains unchanged upon dilution, so you can write this equation. • M1 and V1 are the molarity and volume of the initial solution, and M2 and V2 are the molarity and volume of the diluted solution.
16.2 Making Dilutions • Making a Dilute Solution
16.2 Making Dilutions • To prepare 100 ml of 0.40M MgSO4 from a stock solution of 2.0M MgSO4, a student first measures 20 mL of the stock solution with a 20-mL pipet.
16.2 Making Dilutions • She then transfers the 20 mL to a 100-mL volumetric flask.
16.2 Making Dilutions • Finally she carefully adds water to the mark to make 100 mL of solution.
16.2 Making Dilutions • Volume-Measuring Devices
16.2 Percent Solutions • Percent Solutions • What are two ways to express the percent concentration of a solution? • The concentration of a solution in percent can be expressed in two ways: as the ratio of the volume of the solute to the volume of the solution or as the ratio of the mass of the solute to the mass of the solution.
16.2 Percent Solutions • Concentration in Percent (Volume/Volume)
16.2 Percent Solutions • Isopropyl alcohol (2-propanol) is sold as a 91% solution. This solution consist of 91 mL of isopropyl alcohol mixed with enough water to make 100 mL of solution.
for Sample Problem 16.5 Practice Problems For Sample Problem 16.5
16.2 Percent Solutions • Concentration in percent (mass/mass)
16.2 Parts per million • Concentration in parts per million (ppm) • (To complete)
16.2 Section Quiz. • 16.1.
16.2 Section Quiz. • 1. To make a 1.00M aqueous solution of NaCl, 58.4 g of NaCl are dissolved in • 1.00 liter of water. • enough water to make 1.00 liter of solution • 1.00 kg of water. • 100 mL of water.
16.2 Section Quiz. • 2. What mass of sodium iodide (NaI) is contained in 250 mL of a 0.500M solution? • 150 g • 75.0 g • 18.7 g • 0.50 g
16.2 Section Quiz. • 3. Diluting a solution does NOT change which of the following? • concentration • volume • milliliters of solvent • moles of solute
16.2 Section Quiz. • 4. In a 2000 g solution of glucose that is labeled 5.0% (m/m), the mass of water is • 2000 g. • 100 g. • 1995 g. • 1900 g.
16.2 Section Quiz. • 4. In a 2000 g solution of glucose that is labeled 4.0 ppm, the mass of glucose is • 2000 g. • 100 g. • 1995 g. • 0.0080 g.
