general, organic, and biological chemistry copyright © 2010 pearson education, inc. 1 chapter 8...

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc. 1

Chapter 8 Solutions

8.4Percent Concentration


The concentration of a solution is the amount of solute dissolved in a specific amount

of solution

concentration = amount of soluteamount of solution

Concentration


Mass percent (m/m) concentration is the percent by mass of solute in a solution calculated using the formula:

Mass = mass of solute(g) x 100%percent mass of solute(g) + mass of solvent(g)

Mass percent = mass of solute(g) x 100% mass of solution(g)

Mass Percent Concentration


Mass of Solution


The calculation of mass percent (m/m) requires the grams of solute (g of KCl) and grams of solution (g of 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 of KCl (solute) x 100% = 16.0% (m/m) 50.00 g of KCl solution

Calculating Mass Percent

General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

Guide to Calculating Solution Concentrations

6


A solution is prepared with 15.0 g of Na2CO3 and 235 g of H2O. What is 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

Learning Check


3) 6.00% (m/m) Na2CO3 STEP 1 Given: 15.0 g of Na2CO3; 235 g of H2O

Need: mass percent (m/m) of Na2CO3 solution

STEP 2 Plan: mass percent(m/m) = g of solute x 100% g of solution

Calculate mass of solution

= 15.0 g + 235 g

= 250 g of Na2CO3 solution

Solution


STEP 3 Write equalities and conversion factors: 15.0 g of Na2CO3 = 250 g of solution

15.0 g Na2CO3 and 250 g solution

250 g solution 15.0 g of Na2CO3

STEP 4 Set up problem:

mass = 15.0 g Na2CO3 x 100 = 6.00%(m/m) Na2CO3

percent 250 g solution(m/m)

Solution (continued)


The volume percent (v/v) is percent by volume of solute (liquid) in a solution volume % (v/v) = volume of solute x 100%

volume of solution volume solute (mL) in 100 mL of solution.

volume % (v/v) = mL of solute 100. mL of solution

Volume Percent


The mass/volume percent (m/v) is

mass/volume % (m/v) = grams (g) of solute x 100% volume(mL) of solution

mass of solute(g) in 100 mL solution = g of solute 100. mL of solution

Mass/Volume Percent


Preparation of a Solution: Mass/Volume Percent

12


Percent Conversion Factors

Two conversion factors can be written for each type of percent concentration.


Write two conversion factors for each solution:

A. 8.50% (m/m) NaOH

B. 5.75% (v/v) ethanol

C. 4.8% (m/v) HCl

Learning Check


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) ethanol 5.75 mL ethanol and 100 mL solution

100 mL solution 5.75 mL ethanol

C. 4.8% (m/v) HCl 4.8 g HCl and 100 mL HCl

100 mL solution 4.8 g HCl

Solution


Guide to Using Concentration to Calculate Mass or Volume

16


How many grams of NaCl are needed to prepare225 g of a 10.0% (m/m) NaCl solution?

STEP 1 Given: 225 g of solution; 10.0% (m/m) NaCl Need: g of NaCl (solute)

STEP 2 Plan: g of solution g of NaCl

Example of Using Percent Concentration (m/m) Factors

17


Solution

STEP 3 Write equalities and conversion factors:

10.0 g of NaCl = 100 g of NaCl solution

10.0 g NaCl and 100 g NaCl solution

100 g NaCl solution 10.0 g NaCl

STEP 4 Set up problem to cancel grams of solution:225 g NaCl solution x 10.0 g NaCl = 22.5 g of NaCl

100 g NaCl solution

18


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


Solution

STEP 1 Given: 75.0 g of NaOH solution; 14.0% (m/m) NaOH solution Need: g of NaOH (solute)

STEP 2 g of solution g of NaOH


14.0 g of NaOH = 100 of NaOH solution

14.0 g NaOH and 100 g NaOH solution 100 g NaOH solution 14.0 g NaOHSTEP 4 Set up problem to cancel the grams of solution:

75.0 g NaOH solution x 14.0 g NaOH = 10.5 g of NaOH 100 g NaOH solution

20


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


Solution

STEP 1 Given: 2.25 mL of ethanol (solute)

5.75% (v/v) ethanol solution

Need: mL of ethanol solution

STEP 2 Plan: mL of ethanol mL of solution


100 mL of solution = 5.75 mL of ethanol 5.75 mL ethanol and 100 mL solution

100 mL solution 5.75 mL ethanolSTEP 4 Set up problem to cancel the mL of ethanol:2.25 mL ethanol x 100 mL solution = 39.1 mL of solution

5.75. mL ethanol

22


How many mL of a 4.20% (m/v) will contain 3.15 g KCl?

STEP 1 Given: 3.15 g of KCl (solute) 4.20% (m/v) KCl solution Need: mL of KCl solution

STEP 2 Plan: g of KCl mL of KCl solution

Example Using Percent Concentration (m/v) Factors

23



4.20 g KCl = 100 mL of KCl solution

4.20 g KCl and 100 mL KCl solution

100 mL KCl 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) Factors (continued)


Learning Check

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

1) 7.04 g of NaOH

2) 11.0 g of NaOH

3) 14.2 g of NaOH


Solution

26

2) 11.0 g of NaOH

STEP 1 Given: 125 mL of NaOH (solution) 8.80% (m/v) NaOH solution Need: g of NaOH (solute)

STEP 2 Plan: mL of NaOH solution g of NaOH


Solution (continued)

27

STEP 3 Write equality and conversion factors:

8.80 g of NaOH = 100 mL of NaOH solution

8.80 g NaOH and 100 mL NaOH solution 100 mL NaOH solution 8.80 g NaOH

STEP 4 Set up the problem:

125 mL NaOH solution x 8.80 g NaOH

100 mL NaOH solution

= 11.0 g of NaOH

general, organic, and biological chemistry copyright © 2010 pearson education, inc. 1 chapter 8...

Documents