1

12.5

Molarity and Dilution

Chapter 12 Solutions

Copyright © 2008 by Pearson Education, Inc.Publishing as Benjamin Cummings

2

Molarity (M)Molarity (M) is

• A concentration term for solutions.

• The moles of solute in 1 L solution.

• moles of soluteliter of solution

3

Preparing a 1.0 Molar Solution

A 1.00 M NaCl solution is prepared• By weighing out 58.5 g NaCl (1.00 mol) and• Adding water to make 1.00 liter of solution.

Copyright © 2008 by Pearson Education, Inc.Publishing as Benjamin Cummings

4

Add GPS

Guide to Calculating Molarity

Basic 2e p 394

5

What is the molarity of 0.500 L NaOH solution if itcontains 6.00 g NaOH?STEP 1 Given 6.00 g NaOH in 0.500 L solution

Need molarity (mol/L)

STEP 2 Plan g NaOH mol NaOH molarity

STEP 3 Conversion factors 1 mol NaOH = 40.00 g

1 mol NaOH and 40.00 g NaOH 40.00 g NaOH 1 mol NaOH

Calculation of Molarity

6

STEP 4 Calculate molarity.6.00 g NaOH x 1 mol NaOH = 0.150 mol

40.00 g NaOH

0.150 mol = 0.300 mol = 0.300 M NaOH0.500 L 1 L

Calculation of Molarity (cont.)

7

What is the molarity of 325 mL of a solution containing 46.8 g of NaHCO3?

1) 0.557 M

2) 1.44 M

3) 1.71 M

Learning Check

8

3) 1.71 M

46.8 g NaHCO3 x 1 mol NaHCO3 = 0.557 mol NaHCO3

84.01 g NaHCO3

0.557 mol NaHCO3 = 1.71 M NaHCO3

0.325 L

Solution

9

What is the molarity of a solution if 225 mL contains 34.8 g KNO3?

1) 0.0775 M

2) 1.53 M

3) 15.5 M

Learning Check

10

2) 1.53 M 34.8 g KNO3 x 1 mol KNO3 = 0.344 mol KNO3

101.11g KNO3

M = mol = 0.344 mol KNO3 = 1.53 M

L 0.225 L

In one setup

34.8 g KNO3 x 1 mol KNO3 x 1 = 1.53 M

101.11g KNO3 0.225 L

Solution

11

Molarity Conversion Factors

The units of molarity are used as conversion factors in calculations with solutions.

Table 2.6

Copyright © 2008 by Pearson Education, Inc.Publishing as Benjamin Cummings

12

Molarity in Calculations

How many grams of KCl are needed to prepare

125 mL of a 0.720 M KCl solution?

STEP 1 Given 125 mL (0.125 L) of 0.720 M KCl

Need Grams of KCl

STEP 2 Plan L KCl mol KCl g KCl

13

Molarity in Calculations (cont.)

STEP 3 Conversion factors 1 mol KCl = 74.55 g

1 mol KCl and 74.55 g KCl 74.55 g KCl 1 mol KCl

1 L KCl = 0.720 mol KCl 1 L and 0.720 mol KCl

0.720 mol KCl 1 L

STEP 4 Calculate grams.0.125 L x 0.720 mol KCl x 74.55 g KCl = 6.71 g KCl 1 L 1 mol KCl

14

How many grams of AlCl3 are needed to prepare

125 mL of a 0.150 M solution?

1) 20.0 g AlCl3

2) 16.7g AlCl3

3) 2.50 g AlCl3

Learning Check

15

Solution

3) 2.50 g AlCl3

0.125 L x 0.150 mol x 133.3 g = 2.50 g AlCl3 1 L 1 mol

16

How many milliliters of 2.00 M HNO3 contain

24.0 g HNO3?

1) 12.0 mL

2) 83.3 mL

3) 190. mL

Learning Check

17

3) 190. mL

24.0 g HNO3 x 1 mol HNO3 x 1000 mL

63.02 g HNO3 2.00 mol HNO3

Molarity factor inverted

= 190. mL HNO3

Solution

18

DilutionIn a dilution

• Water is added.

• Volume increases.

• Concentration decreases.

Copyright © 2008 by Pearson Education, Inc.Publishing as Benjamin Cummings

19

Comparing Initial and Diluted Solutions

In the initial and diluted solution

• The moles of solute are the same.

• The concentrations and volumes are related by the equation

M1V1 = M2V2

initial diluted

20

Add GPS

Guide to Calculating Dilution Quantities

Basic 2e p 398

21

Dilution Calculations

What is the molarity if 0.180 L of 0.600 M KOH isdiluted to a final volume of 0.540 L?STEP 1 Prepare a table:

M1= 0.600 MV1 = 0.180 L

M2= ? V2 = 0.540 L

STEP 2 Solve dilution equation for unknown.

M1V1 = M2V2 M1V1/ V2 = M2

STEP 3 Set up and enter values:

M2 = M1V1 = (0.600 M)(0.180 L) = 0.200 M

V2 0.540 L

22

Learning Check

What is the final volume if 15.0 mL of a 1.80 M

KOH is diluted to give a 0.300 M solution?

1) 27.0 mL

2) 60.0 mL

3) 90.0 mL

23

Solution

STEP 1 Prepare a table:

M1= 1.80 M V1 = 15.0 mL

M2= 0.300 M V2 = ?

STEP 2 Solve dilution equation for unknown.

M1V1 = M2V2 V2 = M1V1 / M2

STEP 3 Set up and enter values: V2 = M1V1 = (1.80 M)(15.0 mL) = 90.0 mL M2 0.300 M