Chemistry 1 Chapter 15

1. Chemistry 1Chapter 15 Solution Chemistry Part I Notes # 8b

2. Solutions • Solutions: homogenous mixtures that contain 2 or more substances (solute & solvent) • Solute: substance that dissolves • Solvent: the dissolving substance (ex: water) • Can be solid, liquid, or gas

3. Soluble vs. Insoluble • Soluble: a substance that dissolves in a solvent (ex: Kool Aid in H2O) • Insoluble: a substance that does not dissolve in a solvent (ex: sand in H20)

4. Immiscible vs. Miscible • Immiscible: two liquids that are not soluble (ex: water & oil) • Miscible : two liquids that are soluble (ex: water and vinegar)

5. Dissolving, Dissociation, Solvation

6. Why are some substances soluble and others are not? • Solute particles are completely surrounded by solvent particles • Attractive forces between solvent and solute particles are stronger than the attractive forces holding solute to solute • Solvation: the process of surrounding solute particles with solvent particles to form a solution (called hydration, in water) • Typical Rule: “LIKE DISSOLVES LIKE”

7. Like Dissolves Like • Although water dissolves an enormous variety of substances, both ionic and covalent, it does not dissolve everything. • The phrase that scientists often use when predicting solubility is “like dissolves like.” • The expression means that dissolving occurs when similarities exist between the solvent and the solute.

8. Factors Affecting Solvation (Increasing It) • Agitate the mixture (stir or mix) • Increase surface area of solute (break into smaller chunks of solute before adding solvent) • Increase temperature

9. Solvation

10. Solubility • Def: Maximum amount of solute that will dissolve at a given temperature.

11. Saturation • Saturated: contains the maximum amount of solute that will dissolve in a given amount of solvent at a specified temperature and pressure • Unsaturated: contains less dissolved solute for a given temperature and pressure than that of a saturated solution (more solute can be dissolved) • Super Saturated: contains more dissolved solute than does a saturated solution at the same temperature (these are very unstable)

13. Effect of Temperature on Solubility • Temperature has a significant effect on solubility for most solutes. • The solubilities of some solutes, such as sodium nitrate and potassium nitrate, increase dramatically with increasing temperature.

14. Effect of Temperature on Solubility • Other solutes, like NaCl and KCl, show only slight increases in solubility with increasing temperatures. • A few solutes, like cerium(III) sulfate, Ce2(SO4)3, decrease in solubility as temperature increases.

15. Henry’s Law • States that at a given temperature, the solubility (S) of a gas in a liquid is directly proportional to the pressure (P) of the gas above a liquid. • Discuss Soda Bottle & Fizz Keeper

17. 15.2 Concentrated Versus Dilute • Chemists never apply the terms strong and weak to solution concentrations. • As you’ll see in the next chapter, these terms are used in chemistry to describe the chemical behavior of acids and bases. • Instead, use the terms concentrated and dilute.

18. Solution Concentration • Concentration: the measure of how much solute is dissolved in a specific amount of solvent or solution • Concentrated solution = large amts of solute • Dilute solutions = small amts of solute • Use percent to describe concentration Mass (or Volume) percent =

19. Molarity Solutions Molarity: the number of moles of solute per liter of solution Molarity (M) = Example: What is the molarity of an aqueous solution that contains 14.2 g NaCl dissolved in 2364 mL of the solution?

20. Diluting Solutions • Preparing a less concentrated solution by diluting the stock solution with solvent • Add solvent, decrease concentration • M1V1 = M2V2 • Example: What volume (in milliliters) of a 1.15 M stock solution of potassium nitrate is needed to make a 0.75 L of 0.578M potassium nitrate?

21. Molality Molality: is equal to the number of moles of solute per kilogram of solvent Molality (m) = Example: What is the molality of a solution that contains 16.3 g of potassium chloride dissolved in 845g water?

22. Molarity Solutions Mole Fraction: ratio of the number of moles of solute or solvent to the total number of moles of solute plus solvent in a solution Mole fraction (A) =

23. Solution Composition 1. Molarity (M) = 2. Mass or Volume percent = 3. Mole fraction (A) = 4. Molality (m) =

24. How to make a solution.

25. You must be able to explain how to make a solution.

26. Molarity • Concentration units can vary greatly. • They express a ratio that compares an amount of the solute with an amount of the solution or the solvent. • For chemistry applications, the concentration term molarity is generally the most useful. • Molarity is defined as the number of moles of solute per liter of solution. • Molarity = moles of solute/liter of solution

27. Molarity • In order to be at the same concentration as the salt in the patient’s blood, it needs to have a concentration of 0.15 moles of sodium chloride per liter of solution. • In other words, it must have a molarity of 0.15.

28. Molarity • Note that the volume is the total solution volume that results, not the volume of solvent alone. • Suppose you need 1.0 L of the salt solution mentioned above.

29. Molarity • To save space, you refer to the solution as 0.15M NaCl, where the M stands for “moles/liter” and represents the word molar. • Thus, you need 1.0 L of a 0.15-molar solution of NaCl. How are you going to prepare it?

30. Molarity • Assuming you’re making an aqueous solution, you need to know only three things when working quantitatively: the concentration, the amount of solute, and the total volume of solution needed.

31. Preparing 1 L of an NaCl Solution • How would you prepare 1.0 L of a 0.15M sodium chloride solution? • First, determine the mass of NaCl to add to a 1.0-L container. • The 0.15M solution must contain 0.15 moles of NaCl per liter of solution.

32. Preparing 1 L of an NaCl Solution • The proper setup, showing the conversion factors, is as follows.

33. Preparing 1 L of an NaCl Solution • Then carry out cancellations and calculate the answer.

34. Preparing 1 L of an NaCl Solution • The result means you need to measure 8.8 g of NaCl, add some water to dissolve it, and then add enough additional water to bring the total volume of the solution to 1.0 L.

35. Preparing a Different Volume of a Glucose Solution • How would you prepare 5.0L of a 1.5M solution of glucose, C6H12O6? • You need to determine the number of grams of glucose to add to a 5.0-L container.

36. Preparing a Different Volume of a Glucose Solution • The 1.5M solution must contain 1.5 mol of glucose per liter of solution. • The proper setup, showing the conversion factors, is as follows.

37. Preparing a Different Volume of a Glucose Solution • Cancel units and carry out the calculation.

38. Preparing a Different Volume of a Glucose Solution • The mass of glucose required is 1400 g. • Weigh this mass, add it to a 5.0-L container, add enough water to dissolve the glucose, and fill with water to the 5.0-L mark.

39. Calculating Molarity • You add 32.0 g of potassium chloride to a container and add enough water to bring the total solution volume to 955 mL. What is the molarity of this solution? • You are given that there are 32.0 g of solute per 955 mL of solution, so this relationship can be expressed in fraction form with the volume in the denominator.

40. Calculating Molarity • Therefore, the initial part of the setup is as follows.

41. Calculating Molarity • Determine that the molar mass of KCl is 74.6 g/mol by adding the atomic masses of K and Cl and applying the unit grams/mole to the sum. • The conversion factor that must be used to convert from grams to moles of KCl is 1mol KCl/74.6 g KCl.

42. Calculating Molarity • Next, to convert milliliters to liters, given that there are 1000 mL solution/L solution, use that conversion factor in the setup.

43. Calculating Molarity • Cancel units and carry out the calculation, using the setup just developed.

44. Dilutions • Solution Dilution • M1V1=M2V2