1 Chapter 7 Solutions 7.5 Molarity and Dilution

2 Molarity (M) Molarity (M) is a concentration term for solutions. gives the moles of solute in 1 L 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 NaCl (1.00 mole) and adding water to make 1.00 liter of solution. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

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

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

6 What is the molarity of 325 mL of a solution containing 46.8 g of NaHCO 3 ? 1) M 2) 1.44 M 3) 1.71 M Learning Check

7 3) 1.71 M 46.8 g NaHCO 3 x 1 mole NaHCO 3 = mole NaHCO g NaHCO mole NaHCO 3 = 1.71 M NaHCO L Solution

8 What is the molarity of 225 mL of a KNO 3 solution containing 34.8 g KNO 3 ? 1)0.344 M 2)1.53 M 3)15.5 M Learning Check

9 2)1.53 M 34.8 g KNO 3 x 1 mole KNO 3 = mole KNO g KNO 3 M = mole = mole KNO 3 = 1.53 M L L In one setup: 34.8 g KNO 3 x 1 mole KNO 3 x 1 = 1.53 M g KNO L Solution

10 Molarity Conversion Factors The units of molarity are used as conversion factors in calculations with solutions. TABLE 7.8

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

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

13 How many grams of AlCl 3 are needed to prepare 125 mL of a M solution? 1) 20.0 g AlCl 3 2) 16.7g AlCl 3 3) 2.50 g AlCl 3 Learning Check

14 Solution 3) 2.50 g AlCl L x mole x g = 2.50 g AlCl 3 1 L 1 mole

15 How many milliliters of 2.00 M HNO 3 contain 24.0 g HNO 3 ? 1) 12.0 mL 2) 83.3 mL 3) 190. mL Learning Check

g HNO 3 x 1 mole HNO 3 x 1000 mL = 63.0 g HNO mole HNO 3 Molarity factor inverted = 190. mL HNO 3 Solution

17 D ilution In a dilution water is added. volume increases. concentration decreases.

Mix The amount of solute in the concentrated solution = amount of solute in the diluted solution 3 containers of H 2 O 1 container orange juice concentrate +

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 following equations: For percent concentration: C 1 V 1 = C 2 V 2 initial diluted For molarity: M 1 V 1 = M 2 V 2 initial diluted

20 Dilution Calculations with Percent What volume of a 2.00% (m/v) HCl solution can be prepared by diluting 25.0 mL of 14.0% (m/v) HCl solution? Prepare a table: C 1 = 14.0% (m/v)V 1 = 25.0 mL C 2 = 2.00% (m/v)V 2 = ? Solve dilution equation for unknown and enter values: C 1 V 1 = C 2 V 2 V 2 = V 1 C 1 = (25.0 mL)(14.0%) = 175 mL C %

21 Learning Check What is the percent (% m/v) of a solution prepared by diluting 10.0 mL of 9.00% NaOH to 60.0 mL?

22 Solution What is the percent (%m/v) of a solution prepared by diluting 10.0 mL of 9.00% NaOH to 60.0 mL? Prepare a table: C 1 = 9.00 %(m/v)V 1 = 10.0 mL C 2 = ?V 2 = 60.0 mL Solve dilution equation for unknown and enter values: C 1 V 1 = C 2 V 2 C 2 = C 1 V 1 = (10.0 mL)(9.00%) = 1.50% (m/v) V mL

23 Dilution Calculations with Molarity What is the molarity (M) of a solution prepared by diluting 0.180L of M HNO 3 to L? Prepare a table: M 1 = MV 1 = L M 2 = ?V 2 = L Solve dilution equation for unknown and enter values: M 1 V 1 = M 2 V 2 M 2 = M 1 V 1 = (0.600 M)(0.180 L) = M V L

24 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) 27.0 mL 2) 60.0 mL 3) 90.0 mL

25 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: M 1 = 1.80 MV 1 = 15.0 mL M 2 = 0.300MV 2 = ? Solve dilution equation for V 2 and enter values: M 1 V 1 = M 2 V 2 V 2 = M 1 V 1 = (1.80 M)(15.0 mL) = 90.0 mL M M