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Chapter 7 Solutions and Colloids 7.4 Solution Concentrations 1 Percent Concentration The concentration of a solution is the amount of solute dissolved in a specific amount of solution. amount of solute amount of solution 2 Mass Percent Mass percent (%m/m) is the • concentration is the percent 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 x 100 100 g of solution 3 Mass of Solution Add water to give 50.00 g solution 8.00 g KCl 50.00 g KCl solution Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings 4 Calculating Mass Percent 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) 50.00 g KCl solution x 100 = 16.0% (m/m) 5 Learning Check A solution is prepared by mixing 15.0 g Na2CO3 and 235 g of H2O. Calculate the mass percent (%m/m) of the solution. 1) 15.0% (m/m) Na2CO3 2) 6.38% (m/m) Na2CO3 3) 6.00% (m/m) Na2CO3 6 Solution 3) 6.00% (m/m) Na2CO3 STEP 1 mass solute = 15.0 g Na2CO3 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 g solution 100 STEP 4 Set up problem mass %(m/m) = 15.0 g Na2CO3 x 100 = 6.00% Na2CO3 250. g solution 7 Volume Percent 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 8 Mass/Volume Percent 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 9 Percent Conversion Factors Two conversion factors can be written for each type of % value. TABLE 7.7 5% (m/v) glucose There are 5 g of glucose in 100 mL of solution. 5 g glucose 100 mL solution and 100 mL solution 5 g glucose 10 Learning Check 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 11 Solution A. 8.50 g NaOH 100 g solution and 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 solution 100 mL HCl 4.8 g HCl 12 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 13 Learning Check 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 14 Solution 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 15 Learning Check 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 16 Solution 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 17 Using Percent Concentration(m/v) as Conversion Factors How many mL of a 4.20% (m/v) will contain 3.15 g KCl? STEP 1 Given: 3.15 g KCl(solute); 4.20% (m/v) KCl Need: mL of KCl solution STEP 2 Plan: g KCl mL 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 KCl 4.20 g KCl 18 Learning Check How many grams of NaOH are needed to prepare 125 mL of a 8.80% (m/v) NaOH solution? 19 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 = 100 mL solution 11.0 g NaOH 20