Daily Inquiry :

1. Daily Inquiry: • Many solutions are described as concentrated or dilute. Distinguish between these two terms. • A solution is made by dissolving 4.75 g of NaOH in enough water to form 250 mL of solution. (a) Express the amount of solute in moles. (b) Describe the amount of solution in liters.

2. Today’s Objectives: • Express the concentration of a solution in units of molarity and molality. (SPI 3221.2.3) • Describe how to prepare solutions of given concentration. (SPI 3221.2.4)

3. Concentration of a Solution • Theconcentrationof a solution is a measure of the amount of solute in a given amount of solvent or solution. • Many times solutions are referred to as “dilute” or “concentrated”. • Chemists commonly use two different ways to quantitatively express the concentration of a solution. • Molarity (M) • Molality (m)

4. Molarity (M) • Molarity (M)is the number of moles of solute per liter of solution. moles of solute (mol) • Molarity (M) = -------------------------------- liters of solution (L)

5. Molarity Sample Problems • A solution is made by dissolving 4.75 g of NaOH in enough water to form 250 mL of solution. What is the molarity of the solution? • How many moles of KNO3 are required to form 250 mL of a 0.50 M KNO3 solution?

6. ITS YOUR TURN! • What is the molarity of a solution that contains 28.9 g CaCl2 dissolved in enough water to make 0.78 L of solution? A. 0.33 M B. 0.69 M C. 1.5 M D. 3.0 M

7. Molality (m) • Molality is the concentration of a solution expressed in moles of solute per kilogram of solvent. moles of solute (mol) • Molality (m) = ----------------------------------- kilogram of solvent (kg)

8. Molality Sample Problem • A solution was prepared by dissolving 17.1 g of glucose, C6H12O6, in 275 g of water. What is the molality (m) of this solution?

9. Preparing Solutions • Solutions are commonly prepared by • Using solid solute • Diluting a concentrated solution • When preparing a solution from solid solute, first use the molarity equation determine the mass of the solute required.

10. Preparing a Solution from Solid Solute • An experiment calls for 250 mL of a 0.10 M KMnO4 solution. How many grams of solid KMnO4 are required to make the solution? Explain how you would create this solution.

11. What Do You Think? • How many grams of sodium chloride (NaCl) are required to prepare 500.0 mL of a 0.100 M solution? A. 1.46 g B. 2.93 g C. 29.3 g D. 58.5 g

12. Preparing Solutions from Other Solutions • Many times solutions are prepared by diluting concentrated solutions. These are called stock solutions. • Dilution = process of adding water to a stock solution to achieve the molarity desired for a particular solution. • Adding water increases the volume of the solution and this causes the concentration to decrease. • Dilution Equation: M1V1 = M2V2

13. Preparing a Solution by Dilution • How many milliliters of 12 M HCl stock solution are needed to make 500 mL of a 0.20 M HCl solution? Explain how you would prepare this solution.

14. Practice Question • If 250.0 mL of a 0.96 M solution of acetic acid are diluted to 800.0 mL, what will be the molarity of the final solution? A. 0.19 M B. 0.24 M C. 0.30 M D. 0.77 M

15. After reflecting on today’s lesson, complete three of the sentence starters on your note card and hand it to me as you leave today. Sentence Starters I’ve learned… I was surprised… I’m beginning to wonder… I would conclude… I now realize that… Outcome Sentences