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Chemistry 16.2
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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.
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Molarity How do you calculate the molarity of a solution? 16.2
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A dilute solution is one that contains a small amount of solute.
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.
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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.
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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. The photos show how to make a 0.5-molar (0.5M) solution. a) Add 0.5 mol of solute to a 1-L volumetric flask half filled with distilled water. b) Swirl the flask carefully to dissolve the solute. c) Fill the flask with water exactly to the 1-L mark.
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Swirl the flask carefully to dissolve the solute.
16.2 Molarity Swirl the flask carefully to dissolve the solute. The photos show how to make a 0.5-molar (0.5M) solution. a) Add 0.5 mol of solute to a 1-L volumetric flask half filled with distilled water. b) Swirl the flask carefully to dissolve the solute. c) Fill the flask with water exactly to the 1-L mark.
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Fill the flask with water exactly to the 1-L mark.
16.2 Molarity Fill the flask with water exactly to the 1-L mark. The photos show how to make a 0.5-molar (0.5M) solution. a) Add 0.5 mol of solute to a 1-L volumetric flask half filled with distilled water. b) Swirl the flask carefully to dissolve the solute. c) Fill the flask with water exactly to the 1-L mark.
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for Sample Problem 16.2 Problem Solving 16.8 Solve Problem 8 with the help of an interactive guided tutorial.
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16.3 Sample Problem 16.3
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16.3 Sample Problem 16.3
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16.3 Sample Problem 16.3
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for Sample Problem 16.3 ProblemSolving Solve Problem 11 with the help of an interactive guided tutorial.
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16.2 Making Dilutions Making Dilutions What effect does dilution have on the total moles of solute in a solution?
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16.2 Making Dilutions 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.
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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.
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Making a Dilute Solution
16.2 Making Dilutions Making a Dilute Solution Adding solvent to a concentrated solution lowers the concentration, but the total number of moles of solute present remains the same.
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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. The student is preparing 100 mL of 0.40M MgSO4 from a stock solution of 2.0M MgSO4 . a) She measures 20 mL of the stock solution with a 20-mL pipet. b) She transfers the 20 mL to a 100-mL volumetric flask. c) She carefully adds water to the mark to make 100 mL of solution. Inferring How many significant figures does the new molarity have?
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She then transfers the 20 mL to a 100-mL volumetric flask.
16.2 Making Dilutions She then transfers the 20 mL to a 100-mL volumetric flask. The student is preparing 100 mL of 0.40M MgSO4 from a stock solution of 2.0M MgSO4 . a) She measures 20 mL of the stock solution with a 20-mL pipet. b) She transfers the 20 mL to a 100-mL volumetric flask. c) She carefully adds water to the mark to make 100 mL of solution. Inferring How many significant figures does the new molarity have?
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16.2 Making Dilutions Finally she carefully adds water to the mark to make 100 mL of solution. The student is preparing 100 mL of 0.40M MgSO4 from a stock solution of 2.0M MgSO4 . a) She measures 20 mL of the stock solution with a 20-mL pipet. b) She transfers the 20 mL to a 100-mL volumetric flask. c) She carefully adds water to the mark to make 100 mL of solution. Inferring How many significant figures does the new molarity have?
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Volume-Measuring Devices
16.2 Making Dilutions Volume-Measuring Devices The photo shows a buret, a graduated cylinder, a volumetric flask, and a volumetric pipet. These are just some examples of volume-measuring devices.
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for Sample Problem 16.4 ` Problem Solving Solve Problem 12 with the help of an interactive guided tutorial.
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16.2 Percent Solutions Percent Solutions What are two ways to express the percent concentration of a solution?
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16.2 Percent Solutions 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.
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Concentration in Percent (Volume/Volume)
16.2 Percent Solutions Concentration in Percent (Volume/Volume)
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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. The label clearly distinguishes this solution of isopropyl alcohol from rubbing alcohol, which is a 70% solution of isopropyl alcohol. Applying Concepts How many milliliters of isopropyl alcohol are in 100 mL of 91% alcohol?
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Practice Problems For Sample Problem 16.5
Problem-Solving Solve Problem 15 with the help of an interactive guided tutorial.
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Concentration in Percent (Mass/Mass)
16.2 Percent Solutions Concentration in Percent (Mass/Mass)
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16.2 Section Quiz. 16.2.
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16.2 Section Quiz. 1. To make a 1.00M aqueous solution of NaCl, 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.
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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
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16.2 Section Quiz. 3. Diluting a solution does NOT change which of the following? concentration volume milliliters of solvent moles of solute
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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.
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