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Announcements & Agenda (02/14/07)

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 Decided we will allow you to replace a low test score with your final exam grade if it is higher

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Announcements & Agenda (02/14/07)

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  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 • 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 review @ 3pm, Room TBA • Agenda for the next 5 classes: Ch 7, Ch 8, & Movie • Today • Exam Discussion • Solutions & Solution Properties (7.1-7.3) • 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… • Some struggles with quiz-like questions • Be sure you understand objectives

  3. Exam 1 Results • 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: • About what I expected • A bit challenging, but doable if I studied • Quite challenging – need to study more • Oh my!!! Time to talk to Bob…

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

  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 • Solute – material dissolved in the solvent • They don’t just have to be liquids:

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

  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 molecule • forms hydrogen bonds between the hydrogen atom in one molecule and the oxygen atom in a different water molecule.

  11. Hydrogen Bonding Reminder 0

  12. Formation of an Ionic Solution Na+ and Cl- ions • on the surface of a NaCl crystal are attracted to polar water molecules. • are hydrated in solution with many H2O 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. Equations for Solution Formation When NaCl(s) dissolves in water, the reaction can be written as H2O NaCl(s) Na+(aq) + Cl- (aq) solid separation of ions 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 Solvents Water (polar) CH2Cl2(nonpolar) I2 (nonpolar) Ni(NO3)2 (polar)

  17. Example Which of the following solutes will dissolve in water? Why? 1) Na2SO4 2) gasoline 3) SiCl4 4) HCl Yes, ionic No, nonpolar No, nonpolar Yes, polar Most polar and ionic solutes dissolve in water 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: • 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. Solutes and Ionic Charge In water, • strong electrolytes produce ions and conduct an electric current. • weak electrolytes produce a few ions. • nonelectrolytes do not produce ions.

  21. Strong Electrolytes • dissociate in water producing + & – ions • conduct an electric current • in equations show the formation of ions in aqueous (aq) solutions. H2O 100% ions NaCl(s) Na+(aq) + Cl− (aq) H2O CaBr2(s) Ca2+(aq) + 2Br− (aq)

  22. Weak Electrolytes • dissociate only slightly in water • in water forms a solution of a few ions and mostly undissociated molecules. HF(g) + H2O(l) H3O+(aq) + F- (aq) NH3(g) + H2O(l) NH4+(aq) + OH- (aq)

  23. Nonelectrolytes • dissolve as molecules • do not produce ions • do not conduct an electric current

  24. 0 Electrolytes in the Body • Carry messages send to and from the brain as electrical signals • Maintain cellular function with the correct concentrations electrolytes

  25. 0 Electrolyte balance in cells is important Na+, Ca2+, Cl- K+, Mg+2, X-

  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 Ca2+ = 2 equivalents 1 mole Fe3+ = 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+ 147 mEq/L Cl− 155 mEq/L K+ 4 mEq/L Ca2+ 4 mEq/L The milliequivalents per liter of cations must equal the milliequivalents per liter of anions.

  28. Solubility & Concentration (7.3-7.4) • the maximum amount of solute that dissolves in a specific amount of solvent. • expressed as grams of solute in 100 grams of solvent water. g of solute 100 g water Unsaturated vs. Saturated Solutions

  29. Learning Check At 40C, the solubility of KBr is 80 g/100 g H2O. 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. What happens to the “leftover” solute???

  30. Effect of Temperature on Solubility • Depends on Temp! • Solids: usually increases 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 liquid • at higher pressures, more gas molecules dissolve in the liquid. Real life examples… soda, the bends, etc.

  32. Percent Concentration (7.4) 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 • Volume Percent • Mass/Volume Percent • Molarity

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

  34. Mass of Solution Add water to give 50.00 g solution 8.00 g KCl 50.00 g KCl solution

  35. Calculating Mass Percent Calculation of mass percent (% m/m) requires the • grams of solute (g KCl) and • grams of solution (g KCl solution). g of KCl = 8.00 g g of solvent (water) = 42.00 g g of KCl solution = 50.00 g 8.00 g KCl (solute) x 100 = 16.0% (m/m) 50.00 g KCl solution

  36. Volume Percent (% v/v) • 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. volume % (v/v) = mL of solute 100 mL of solution

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

  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 mLof 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

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

  41. How many milliliters of a 5.75% (v/v) ethanol solution can be prepared from 2.25 mL ethanol? 1) 2.56 mL 2) 12.9 mL 3) 39.1 mL

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

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