# 1 Chapter 12Solutions 12.4 Percent Concentration Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings.

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1 Chapter 12Solutions 12.4 Percent Concentration Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

2 The concentration of a solution Is the amount of solute dissolved in a specific amount of solution. amount of solute amount of solution As percent concentration describes the amount of solute that is dissolved in 100 parts of solution. amount of solute 100 parts solution Percent Concentration

3 The mass percent (%m/m) Concentration is the percent by mass of solute in a solution. mass percent (%m/m) = g of solute x 100 g of solute + g of solvent Is the g of solute in 100 g of solution. mass percent = g of solute x 100 100 g of solution Mass Percent

4 Mass of Solution Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

5 Mass percent (%m/m) is calculated from the grams of solute (g KCl) and the grams of solution (g KCl solution). g of KCl = 8.00 g g of solvent (water) = 42.00 g g of KCl solution = 50.00 g 8.00 g KCl (solute) x 100 = 16.0% (m/m) 50.00 g KCl solution Calculating Mass Percent

6 A solution is prepared by mixing 15.0 g Na 2 CO 3 and 235 g of H 2 O. Calculate the mass percent (%m/m) of the solution. 1) 15.0% (m/m) Na 2 CO 3 2) 6.38% (m/m) Na 2 CO 3 3) 6.00% (m/m) Na 2 CO 3 Learning Check

7 3) 6.00% (m/m) Na 2 CO 3 mass solute = 15.0 g Na 2 CO 3 mass solution= 15.0 g + 235 g = 250. g mass %(m/m) = 15.0 g Na 2 CO 3 x 100 250. g solution = 6.00% Na 2 CO 3 solution Solution

8 The volume percent (%v/v) is Percent volume (mL) of solute (liquid) to volume (mL) of solution. volume % (v/v) = mL of solute x 100 mL of solution Solute (mL) in 100 mL of solution. volume % (v/v) = mL of solute 100 mL of solution Volume Percent

9 Percent Conversion Factors Two conversion factors can be written for each type of % value. Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings Table 12.5

10 Write two conversion factors for each solutions: A. 8.50%(m/m) NaOH B. 5.75%(v/v) ethanol Learning Check

11 A. 8.50%(m/m) NaOH 8.50 g NaOH and 100 g solution 100 g solution 8.50 g NaOH B. 5.75%(v/v) ethyl alcohol 5.75 mL alcohol and 100 mL solution 100 mL solution 5.75 mL alcohol Solution

12 How many grams of NaCl are needed to prepare 225 g of a 10.0% (m/m) NaCl solution? STEP 1 Given: 225 g solution; 10.0% (m/m) NaCl Need: g of NaCl STEP 2 g solution g NaCl STEP 3 Write the 10.0 %(m/m) as conversion factors. 10.0 g NaCl and 100 g solution 100 g solution 10.0 g NaCl STEP 4 Set up problem to calculate g NaCl. 225 g solution x 10.0 g NaCl = 22.5 g NaCl 100 g solution Using Percent Factors

13 How many grams of NaOH are needed to prepare 75.0 g of 14.0%(m/m) NaOH solution? 1)10.5 g NaOH 2) 75.0 g NaOH 3)536 g NaOH Learning Check

14 1)10.5 g NaOH 75.0 g x 14.0 g NaOH = 10.5 g NaOH 100 g 14.0 % (m/m) factor Solution

15 How many milliliters of a 5.75 % (v/v) ethanol solution can be prepared from 2.25 mL ethanol? 1) 2.56 mL 2) 12.9 mL 3) 39.1 mL Learning Check

16 3) 39.1 mL 2.25 mL ethanol x 100 mL solution 5.75 mL ethanol 5.75 %(v/v) inverted = 39.1 mL solution Solution