1. Chapter 7 Solutions 7.5 Molarity and Dilution
Copyright © by Pearson Education, Inc.

2. Molarity (M) Molarity (M) is a concentration term for solutions.
gives the moles of solute in 1 L of solution.
moles of solute
liter of solution

3. Preparing a 1.0 Molar Solution
A 1.00 M NaCl solution is prepared
by weighing out 58.5 g of NaCl (1.00 mole) and
adding water to make 1.00 liter of solution.
Copyright © by Pearson Education, Inc.

4. Calculation of Molarity
What is the molarity of L of NaOH solution if it
contains 6.00 g of NaOH?
STEP 1: Given g of NaOH in L of solution
Need molarity (mole/L)
STEP 2: Plan g NaOH mole NaOH molarity

5. Calculation of Molarity (continued)
STEP 3: Conversion factors 1 mole of NaOH = 40.0 g
of NaOH
1 mole NaOH and g NaOH
40.0 g NaOH mole NaOH
STEP 4: Calculate molarity.
6.00 g NaOH x 1 mole NaOH = mole
40.0 g NaOH
0.150 mole = mole = M NaOH
0.500 L L

6. Learning Check
What is the molarity of 325 mL of a solution containing g of NaHCO3?
1) M
2) M
3) M

7. Solution 3) 1.71 M 46.8 g NaHCO3 x 1 mole NaHCO3 = 0.557 mole NaHCO3
0.557 mole of NaHCO3 = M NaHCO3
0.325 L

8. Learning Check
What is the molarity of 225 mL of a KNO3 solution containing 34.8 g of KNO3?
1) M
2) 1.53 M
3) 15.5 M

9. Solution 2) 1.53 M 34.8 g KNO3 x 1 mole KNO3 = 0.344 mole of KNO3
M = mole = mole KNO3 = 1.53 M
L L
In one setup:
34.8 g KNO3 x 1 mole KNO3 x = M
101.1 g KNO L

10. Molarity Conversion Factors
The units of molarity are used as conversion factors in calculations with solutions.
Molarity Equality
3.5 M HCl 1 L = 3.5 moles of HCl
Written as Conversion Factors
3.5 moles HCl and L
1 L moles HCl

11. Calculations Using Molarity
How many grams of KCl are needed to prepare 125 mL
of a M KCl solution?
STEP 1: Given mL (0.125 L) of M KCl
Need g of KCl
STEP 2: Plan L KCl moles KCl g KCl

12. Calculations Using Molarity
STEP 3: Conversion factors
1 mole of KCl = 74.6 g
1 mole KCl and g KCl
74.6 g KCl mole KCl
1 L KCl = mole of KCl
1 L and mole KCl
0.720 mole KCl L
STEP 4: Calculate grams.
0.125 L x mole KCl x g KCl = 6.71 g of KCl
1 L mole KCl

13. Learning Check 125 mL of a 0.150 M solution? 1) 20.0 g of AlCl3
How many grams of AlCl3 are needed to prepare
125 mL of a M solution?
1) g of AlCl3
2) g of AlCl3
3) g of AlCl3

14. Solution
3) g AlCl3
0.125 L x mole x g = 2.50 g of AlCl3
1 L mole

15. Learning Check How many milliliters of 2.00 M HNO3 contain 24.0 g of
1) mL
2) mL
3) mL

16. Solution 24.0 g HNO3 x 1 mole HNO3 x 1000 mL
63.0 g HNO mole HNO3
Molarity factor inverted
= mL of HNO3

17. Dilution In a dilution water is added. volume increases.
concentration decreases.
Copyright © by Pearson Education, Inc.

18. 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 following equations:
For percent concentration:
C1V1 = C2V2
initial diluted
For molarity:
M1V1 = M2V2

19. Guide to Calculating Dilution Quantities
Copyright © by Pearson Education, Inc.

20. Dilution Calculations with Molarity
What is the molarity (M) of a solution prepared
by diluting L of M HNO3 to L?
Prepare a table:
M1= M V1 = L
M2= ? V2 = L
Solve dilution equation for unknown and enter values:
M1V1 = M2V2
M = M1V1 = (0.600 M)(0.180 L) = M
V L

21. Learning Check What is the final volume (mL) of 15.0 mL of a 1.80 M
KOH diluted to give a M solution?
1) mL
2) mL
3) mL

22. Solution What is the final volume (mL) of 15.0 mL of a 1.80 M
KOH diluted to give a M solution?
Prepare a table:
M1= M V1 = mL
M2= M V2 = ?
Solve dilution equation for V2 and enter values:
M1V1 = M2V2
V = M1V1 = (1.80 M)(15.0 mL) = mL
M M