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Chapter 12 Solutions

12.4 Percent Concentration

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

amount of solution

amount of soluteamount of solution

• as percent concentration describes the amount of solute that is dissolved in 100 parts of solution

amount of solute100 parts solution

Percent Concentration

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The mass percent (m/m)

• concentration is the percent by mass of solute in a solution

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

• is the g of solute in exactly100 g of solution Mass percent = g of solute x 100%

100. g of solution

Mass Percent

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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

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Mass of Solution

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Calculating Solution Concentration

6

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A solution is prepared by mixing 15.0 g of Na2CO3 and 235 g of H2O. Calculate the mass percent (m/m) of the solution.

A. 15.0% (m/m) Na2CO3

B. 6.38% (m/m) Na2CO3

C. 6.00% (m/m) Na2CO3

Learning Check

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STEP 1 Determine quantities of solute and solution.

Mass of solute = 15.0 g of Na2CO3

Mass of water = 235 g of water

Mass of solution = 250. g of Na2CO3 solution

STEP 2 Write the % concentration expression.

Mass percent (m/m) = grams of Na2CO3 x 100% grams of Na2CO3 solution

Solution

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STEP 3 Substitute solute and solution quantities into the expression

Mass percent (m/m) = 15.0 g Na2CO3 x 100%

250. g Na2CO3 solution

= 6.00% (m/m) Na2CO3 solution

(C)

Solution (continued)

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The volume percent (v/v) is

• percent volume (mL) of solute (liquid) to volume (mL) of solution

Volume percent(v/v) = mL of solute x 100% mL of solution

• solute (mL) in 100 mL of solution

Volume percent (v/v) = mL of solute x 100% 100 mL of solution

Volume Percent

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A volume percent (v/v) solution is prepared by

• using a specific volume (mL) of solute (liquid)

• adding water to the volume line

Volume Percent

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Percent Conversion Factors

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

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Write two conversion factors for each solution.

A. 8.50% (m/m) NaOH

B. 5.75% (v/v) ethanol

Learning Check

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A. 8.50% (m/m) NaOH solution

100 g of NaOH solution = 8.50 g of NaOH

8.50 g NaOH and 100 g NaOH solution

100 g NaOH solution 8.50 g NaOH

B. 5.75% (v/v) ethanol solution

100 mL of ethanol solution = 5.75 mL of ethanol

5.75 mL ethanol and 100 mL solution

100 mL solution 5.75 mL ethanol

Solution

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Using Concentration to Calculate Mass or Volume

15

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How many grams of NaCl are needed to prepare

225 g of a 10.0% (m/m) NaCl solution?

STEP 1 State the given and needed quantities. Given 225 g of NaCl solution; 10.0% (m/m) NaCl solution

Need grams of NaCl

STEP 2 Write a plan to calculate mass or volume.

grams of NaCl solution grams of NaCl

Example of Using Percent Factors

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STEP 3 Write equalities and conversion factors. 100 g of NaCl solution = 10.0 g of NaCl

10.0 g NaCl and 100 g NaCl solution 100 g NaCl solution 10.0 g NaCl

STEP 4 Set up problem to calculate mass or volume.

225 g NaCl solution x 10.0 g NaCl = 22.5 g of NaCl 100 g NaCl solution

Example of Using Percent Factors (continued)

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How many grams of NaOH are needed to prepare 75.0 g of a 14.0% (m/m) NaOH solution?

A. 10.5 g of NaOHB. 75.0 g of NaOH

C. 536 g of NaOH

Learning Check

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STEP 1 State the given and needed quantities.

Given 75.0 g of NaOH of a 14.0% (m/m) solution

Need grams of NaOH

STEP 2 Write a plan to calculate mass or volume.

grams of NaOH solution grams of NaOH

Solution

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STEP 3 Write equalities and conversion factors. 100 g of NaOH solution = 14.0 g of NaOH 14.0 g NaOH and 100 g solution 100 g solution 14.0 g NaOH

STEP 4 Set up problem to calculate mass or volume.

75.0 g solution x 14.0 g NaOH = 10.5 g of NaOH (A)

100 g solution 14.0 % (m/m) factor

Solution (continued)

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How many milliliters of a 5.75% (v/v) ethanol solution can be prepared from 2.25 mL of ethanol?

A. 2.56 mL

B. 12.9 mL

C. 39.1 mL

Learning Check

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STEP 1 State the given and needed quantities.

Given 2.25 ml of ethanol

5.75% (v/v) ethanol solution

Need milliliters of ethanol solution

STEP 2 Write a plan to calculate mass or volume.

mL of ethanol mL of ethanol solution

Solution

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STEP 3 Write equalities and conversion factors. 100 mL of ethanol solution = 5.75 mL of ethanol 5.75 mL ethanol and 100 mL solution 100 mL solution 14.0 mL ethanol

STEP 4 Set up problem to calculate mass or volume.

5.75% (v/v) inverted

2.25 mL ethanol x 100 mL ethanol solution 5.75 mL ethanol

= 39.1 mL of solution (C)

Solution (continued)