 # 1 Chapter 7Solutions 7.4 Percent Concentration Copyright © 2009 by Pearson Education, Inc.

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1 Chapter 7Solutions 7.4 Percent Concentration Copyright © 2009 by Pearson Education, Inc.

2 The concentration of a solution is the amount of solute dissolved in a specific amount of solution. amount of solute amount of solution Percent Concentration

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

4 Mass of Solution 8.00 g KCl 50.00 g of KCl solution Add water to give 50.00 g of solution Copyright © 2009 by Pearson Education, Inc.

5 The calculation of mass percent (% m/m) requires the grams of solute (g KCl) and 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

Guide to Calculating Solution Concentrations 6 Copyright © 2009 by Pearson Education, Inc.

7 A solution is prepared by mixing 15.0 g of 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

8 3) 6.00% (m/m) Na 2 CO 3 STEP 1: mass solute = 15.0 g of Na 2 CO 3 mass solution = 15.0 g + 235 g = 250. g STEP 2: Use g solute/g solution ratio STEP 3: mass %(m/m) =g solute x 100 g solution STEP 4: Set up problem mass %(m/m) = 15.0 g Na 2 CO 3 x 100 = 6.00% Na 2 CO 3 250. g solution Solution

9 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

10 The mass/volume percent (% m/v) is percent mass (g) of solute to volume (mL) of solution. mass/volume % (m/v) = g of solute x 100 mL of solution solute (g) in 100 mL of solution. mass/volume % (m/v) = g of solute 100 mL of solution Mass/Volume Percent

11 Percent Conversion Factors Two conversion factors can be written for each type of % value. Copyright © 2009 by Pearson Education, Inc.

12 Write two conversion factors for each solutions. A. 8.50% (m/m) NaOH B. 5.75% (v/v) ethanol C. 4.8% (m/v) HCl Learning Check

13 A. 8.50 g NaOH and 100 g solution 100 g solution 8.50 g NaOH B. 5.75 mL alcohol and 100 mL solution 100 mL solution 5.75 mL alcohol C. 4.8 g HCl and 100 mL HCl 100 mL solution 4.8 g HCl Solution

14 Using Percent Concentration (m/m) as Conversion Factors 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 using the factor that cancels g solution. 225 g solution x 10.0 g NaCl = 22.5 g NaCl 100 g solution

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

16 1)10.5 g NaOH 75.0 g solution x 14.0 g NaOH = 10.5 g NaOH 100 g solution 14.0% (m/m) factor Solution

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

18 3) 39.1 mL 2.25 mL ethanol x 100 mL solution 5.75 mL ethanol 5.75% (v/v) inverted = 39.1 mL of solution Solution

19 How many mL of a 4.20% (m/v) will contain 3.15 g of KCl? STEP 1: Given: 3.15 g of KCl(solute); 4.20% (m/v) KCl Need: mL of KCl solution STEP 2: Plan: g of KCl mL of KCl solution STEP 3: Write conversion factors. 4.20 g KCl and 100 mL solution 100 mL solution 4.20 g KCl STEP 4: Set up the problem 3.15 g KCl x 100 mL KCl solution = 75.0 mL of KCl 4.20 g KCl Using Percent Concentration (m/v) as Conversion Factors

20 Learning Check How many grams of NaOH are needed to prepare 125 mL of a 8.80% (m/v) NaOH solution?

21 Solution How many grams of NaOH are needed to prepare 125 mL of a 8.80% (m/v) NaOH solution? 125 mL solution x 8.80 g NaOH = 11.0 g of NaOH 100 mL solution