1 Announcements & Agenda (02/14/07) Happy Valentine’s Day! Please pick up your exams up front. GOOD NEWS Exam average was a ~76% - Nice job Exam average was a ~76% - Nice job Decided we will allow you to replace a low test score with your final exam grade if it is higher Decided we will allow you to replace a low test score with your final exam grade if it is higher Starting next Wed - will hold an unofficial weekly 3pm, Room TBA Starting next Wed - will hold an unofficial weekly 3pm, Room TBA Agenda for the next 5 classes: Ch 7, Ch 8, & Movie Today Exam Discussion Exam Discussion Solutions & Solution Properties ( ) Solutions & Solution Properties ( ) Solution Concentrations (7.4) Solution Concentrations (7.4)

2 General Observations Nice class average (~76%) – nice job! Show as much work as possible tried to give as much partial credit as I could… tried to give as much partial credit as I could… Some struggles with quiz-like questions Some struggles with quiz-like questions Be sure you understand objectives Be sure you understand objectives

3 Exam 1 Results What to do if….? What to do if….?  Go over the test – figure out what & why?  Make a plan…  Come visit me to evaluate your situation…

4 Test 1 was: 1.About what I expected 2.A bit challenging, but doable if I studied 3.Quite challenging – need to study more 4.Oh my!!! Time to talk to Bob… 12345

5 For those who did well… What did you do to be successful? 1.Solving problems, reviewing quizzes 2.Reviewing lectures 3.Reading the book 4.Working with somebody else 5.Just lots of time on all of the above 12345

6 CHAPTER 7: SOLUTIONS!

7 Nature of Solutions Solution – homogeneous mixture of two or more substances Solvent – the main medium, present in the largest quantity Solvent – the main medium, present in the largest quantity Solute – material dissolved in the solvent Solute – material dissolved in the solvent They don’t just have to be liquids:

8 Solutes are spread evenly throughout the solution.spread evenly throughout the solution. cannot be separated by filtration.cannot be separated by filtration. can be separated by evaporation.can be separated by evaporation. are not visible, but can give a color to the solution.are not visible, but can give a color to the solution. Nature of Solutes in Solutions

9 Determination of Solubility Definitions you may already know: Solubility of solutes vary tremendously… Miscible: when two liquids mix in all proportions (Acetone and Water) Immiscible: when two liquids DO NOT mix at all (Oil and water) Insoluble: when a solid does not dissolve in a solvent (NaCl in gasoline) Saturated: a solution that has dissolved the maximum possible solute REALITY IS USUALLY SOMEWHERE IN BETWEEN!

10 Water: Nature’s Solvent is a polar moleculeis a polar molecule forms hydrogen bonds between the hydrogen atom in one molecule and the oxygen atom in a different water molecule.forms hydrogen bonds between the hydrogen atom in one molecule and the oxygen atom in a different water molecule.

11 Hydrogen Bonding Reminder

12 Formation of an Ionic Solution Na + and Cl - ions on the surface of a NaCl crystal are attracted to polar water molecules.on the surface of a NaCl crystal are attracted to polar water molecules. are hydrated in solution with many H 2 O molecules surrounding each ion.are hydrated in solution with many H 2 O molecules surrounding each ion.

13 Solubility of Salts Must overcome strong +/- love between ions of the salt (called lattice energy) Solution (pun intended) to the problem: ion-dipole interactions – strength in numbers

14 When NaCl(s) dissolves in water, the reaction can be written as H 2 O H 2 O NaCl(s) Na + (aq) + Cl - (aq) solid separation of ions solid separation of ions Equations for Solution Formation This is reality in ionic solutions!!!

15 “Like Dissolves Like” What does this mean? Answer: compatibility of intermolecular forces (last week) Typically, compounds with similar polarity will be soluble in each other. Predicting trends based on properties…

16 Like Dissolves Like Like Dissolves Like Solvents Solvents Water (polar) Water (polar) CH 2 Cl 2 (nonpolar) CH 2 Cl 2 (nonpolar) I 2 (nonpolar) I 2 (nonpolar) Ni(NO 3 ) 2 (polar) (polar)

17 Which of the following solutes will dissolve in water? Why? 1) Na 2 SO 4 2) gasoline 3) SiCl 4 4) HCl Example Yes, ionic No, nonpolar Yes, polar Most polar and ionic solutes dissolve in water because water is a polar solvent. because water is a polar solvent.

18 Which of the following vitamins are fat-soluble and which are water soluble? Vitamins: organic molecules required for proper function but not made by the body. (Obtain by eating!) 2 categories: 2 categories: fat-soluble (dissolve in fatty hydrocarbon-like tissues) water-soluble Why we need at least some oil & fat in our diet!

19 Electrolytes & Nonelectrolytes (7.2)

20 In water, strong electrolytes produce ions and conduct an electric current.strong electrolytes produce ions and conduct an electric current. weak electrolytes produce a few ions.weak electrolytes produce a few ions. nonelectrolytes do not produce ions.nonelectrolytes do not produce ions. Solutes and Ionic Charge

21 dissociate in water producing + & – ionsdissociate in water producing + & – ions conduct an electric currentconduct an electric current in equations show the formation of ions in aqueous (aq) solutions.in equations show the formation of ions in aqueous (aq) solutions. H 2 O 100% ions H 2 O 100% ions NaCl(s) Na + (aq) + Cl − (aq) H 2 O H 2 O CaBr 2 (s) Ca 2+ (aq) + 2Br − (aq) Strong Electrolytes

22 dissociate only slightly in waterdissociate only slightly in water in water forms a solution of a few ions and mostly undissociated molecules.in water forms a solution of a few ions and mostly undissociated molecules. HF(g) + H 2 O(l) H 3 O + (aq) + F - (aq) NH 3 (g) + H 2 O(l) NH 4 + (aq) + OH - (aq) NH 3 (g) + H 2 O(l) NH 4 + (aq) + OH - (aq) Weak Electrolytes

23 Nonelectrolytes dissolve as moleculesdissolve as molecules do not produce ionsdo not produce ions do not conduct an electric currentdo not conduct an electric current

24 Electrolytes in the Body  Carry messages send to and from the brain as electrical signals  Maintain cellular function with the correct concentrations electrolytes

25 Electrolyte balance in cells is important K +, Mg +2, X - Na +, Ca 2+, Cl -

26 Equivalents An equivalent (Eq) is the amount of an electrolyte or an ion that provides 1 mole of electrical charge (+ or -). 1 mole Na + = 1 equivalent 1 mole Cl − = 1 equivalent 1 mole Ca 2+ = 2 equivalents 1 mole Fe 3+ = 3 equivalents

27 Electrolytes in Body Fluids In replacement solutions for body fluids, the electrolytes are given in milliequivalents per liter (mEq/L). Ringer’s Solution Na mEq/LCl − 155 mEq/L Na mEq/LCl − 155 mEq/L K + 4 mEq/L K + 4 mEq/L Ca 2+ 4 mEq/L Ca 2+ 4 mEq/L The milliequivalents per liter of cations must equal the milliequivalents per liter of anions. The milliequivalents per liter of cations must equal the milliequivalents per liter of anions.

28 the maximum amount of solute that dissolves in a specific amount of solvent.the maximum amount of solute that dissolves in a specific amount of solvent. expressed as grams of solute in 100 grams of solvent water.expressed as grams of solute in 100 grams of solvent water. g of solute g of solute 100 g water Solubility & Concentration ( ) Unsaturated vs. Saturated Solutions

29 At 40  C, the solubility of KBr is 80 g/100 g H 2 O. Identify the following solutions as either 1) saturated or 2) unsaturated. Explain. A. 60 g KBr added to 100 g of water at 40  C. B. 200 g KBr added to 200 g of water at 40  C. C. 25 g KBr added to 50 g of water at 40  C. Learning Check What happens to the “leftover” solute???

30 Effect of Temperature on Solubility Depends on Temp!Depends on Temp! Solids: usually increases as temperature inc.Solids: usually increases as temperature inc. Gases: usually decreases as temperature inc.Gases: usually decreases as temperature inc.

31 Solubility and Pressure Henry’s Law: Gas solubility is directly related to gas pressure above the liquidGas solubility is directly related to gas pressure above the liquid at higher pressures, more gas molecules dissolve in the liquid.at higher pressures, more gas molecules dissolve in the liquid. Real life examples… soda, the bends, etc.

32 The amount of solute dissolved in a specific amount of solution. amount of solute amount of solution Comes in all sorts of fantastic flavors! Mass Percent Mass Percent Volume Percent Volume Percent Mass/Volume Percent Mass/Volume Percent Molarity Molarity Percent Concentration (7.4)

33 concentration is the percent by mass of solute in a solution.concentration is the percent by mass of solute in a solution. mass percent = g of solute x 100 g of solute + g of solvent g of solute + g of solvent amount in g of solute in 100 g of solution.amount in g of solute in 100 g of solution. mass percent = g of solute x 100 mass percent = g of solute x g of solution 100 g of solution Mass Percent (% m/m)

34 Mass of Solution 8.00 g KCl g KCl solution Add water to give g solution

35 Calculation of mass percent (% m/m) requires the grams of solute (g KCl) andgrams of solute (g KCl) and grams of solution (g KCl solution).grams of solution (g KCl solution). g of KCl = 8.00 g g of solvent (water) = g g of KCl solution = g 8.00 g KCl (solute) x 100 = 16.0% (m/m) 8.00 g KCl (solute) x 100 = 16.0% (m/m) g KCl solution g KCl solution Calculating Mass Percent

36 percent volume (mL) of solute (liquid) to volume (mL) of solution.percent volume (mL) of solute (liquid) to volume (mL) of solution. volume % (v/v) = mL of solute x 100 mL of solution solute (mL) in 100 mL of solution.solute (mL) in 100 mL of solution. volume % (v/v) = mL of solute 100 mL of solution Volume Percent (% v/v)

37 percent mass (g) of solute to volume (mL) of solution.percent mass (g) of solute to volume (mL) of solution. mass/volume % (m/v) = g of solute x 100 mL of solution solute (g) in 100 mL of solution.solute (g) in 100 mL of solution. mass/volume % (m/v) = g of solute x mL of solution Mass/Volume Percent (% m/v)

38 Percent Conversion Factors Two conversion factors can be written for each type of % value. TABLE 7.7 5% (m/v) glucose There are 5 g of glucose 5 g glucose and 100 mL solution in 100 mL of solution. 100 mL solution 5 g glucose

39 How many grams of NaOH are needed to prepare 75.0 g of 14.0% (m/m) NaOH solution? 1) 10.5 g NaOH 2) 75.0 g NaOH 3) 536 g NaOH 12345

40 1)10.5 g NaOH 75.0 g solution x 14.0 g NaOH = 10.5 g NaOH 100 g solution 100 g solution 14.0% (m/m) factor 14.0% (m/m) factor Solution

41 How many milliliters of a 5.75% (v/v) ethanol solution can be prepared from 2.25 mL ethanol? ) 2.56 mL 2) 12.9 mL 3) 39.1 mL

42 3) 39.1 mL 2.25 mL ethanol x 100 mL solution 5.75 mL ethanol 5.75% (v/v) inverted 5.75% (v/v) inverted = 39.1 mL solution Solution