Advanced Chemistry

1. Advanced Chemistry • Chapter 13 Solutions

2. What’s a Solution? • Solutions - Solute in the solvent • Many types involving many phases

3. Like Dissolves Like.. • Vitamins • Vitamins B,C are water soluble  Need to be replaced daily • Vitamins A, E, F and G are FAT soluble  Last longer in our fat

4. Intermolecular Forces and Solutions • Intermolecular forces exist in solutions • Ex: Hydration (solvation) - polar water molecules surround ions in solution

5. Solution Formation and Energy • Solution Formation = Energy Change = Enthalpy of Solution Hsoln • Solution Formation --> 3 steps • First step, overcome intermolecular forces - separate solute particles - endothermic • Second step, overcome intermolecular forces separate solvent particles - endothermic step • Third step, solute + solvent particles are attracted to one another, causing formation of solute-solvent interactions - exothermic

6. Put in little amount Put in large amount Purple = endothermic Red = exothermic

7. Factors Affecting Solubility • Solubility of one substance in another depends in part on the nature of the particles involved • Three-step process if the energy return in step 3 of the dissolution process does not at least equal, or nearly equal, the energy that was expended in steps 1 and 2, the dissolution will not happen spontaneously. • The energy return in step 3 depends on the magnitude of attractive forces between solvent and solute particles.

8. Driving Force • The driving force behind solution formation • is the increased disorder achieved when • solvent and solute are mixed. - entropy! • In general, processes that increase disorder • tend to be spontaneous.

9. Saturation • Unsaturated - not enough • Saturated - perfect amount • Supersaturated - more than enough!

10. Solubility in Gases • Solubility increases with increasing molar mass for these gases • Why - primary forces are dispersion forces..these increase with molar mass If mass (=), more polar has higher solubility due to dipole interactions

11. Solubility and Polarity Relationship What causes the difference in solubilities

12. Solubility and Polarity • The –OH group is polar and can engage in hydrogen bonding with water. • Carbon chains are nonpolar and typically insoluble in water. • The longer the carbon chain gets, the more nonpolar character the molecule exhibits • With very long carbon chains, the polarity of the –OH group becomes less and less significant in the behavior of the molecule.

13. Pressure and Solubility • How does solubility affect liquids and solids…it doesn’t! • But it does affect solubility of gases • Increase pressure drives gas into solution • We look at how...

14. Henry’s Law • The solubility of a gas is directly proportional to the partial pressure of the gas over the solution. This relationship is known as Henry’s Law

15. Henry’s Law Practice Problem • Calculate the concentration of CO2 in a soft drink that is bottled with a partial pressure of CO2 of 4.0 atm over the liquid at 25°C. The Henry Law constant for CO2 in water at this temperature is 3.1 x 10-2mol/L◦atm.

16. Solubility: Gases vs. Solids end

17. Scuba Diving • Breathing gas under pressure can present a myriad of possible medical problems. • One of these is decompression sickness or "the bends," caused by breathing nitrogen or other gases under pressure, which are not metabolized by the body. • Click HERE to watch the short video End lecture 1

18. Advanced Chemistry • Concentration

19. How Strong is a Solution? • Concentrations can be expressed quantitatively and qualitatively.. • Concentrated..dilute..according to whom? • Small concentration = dilute • Large Concentration = strong • Quantitative terms are much more specific Qualitative

20. Quantitative Terms • There are many specific ways to state the concentration of a solution • We will learn: • Mass Percentage, ppm and ppb • Mole Fraction, Molarity and Molality • Conversion of Concentration Units (show concentration in many ways!)

21. Expressing Concentration • Several ways: • Mass % • ppm • ppb

22. Mass Percentage • Used to determine the mass percentage of a part in a whole Mass of Comp in Soln X 100 Mass % of Component = Total Mass of Soln

23. Parts per Million - ppm • Used to express the concentration of very dilute solutions.. Mass of comp in soln ppm of comp = X 106 Total mass of soln

24. Parts per Billion - ppb Used to express the concentration of very, very dilute solutions.. Mass of comp in soln ppm of comp = X 109 Total mass of soln

25. Expressing Concentration • Several ways con’t: • Mole Fraction • Molarity • Molality

26. Mole Fraction, Molarity and Molality • These methods are used to express concentrations in terms of numbers of moles of one or more moles in solution • The solute is in moles • The solvent can be in moles or mass amounts

27. Mole Fraction • The mole fraction is used to determine the fractional amount of the solute in the total solution Mole of comp Mole fraction of comp = Total moles of all comp in soln X is the symbol used for mole fraction

28. Molarity • Duh…you guys know this! • Used to state the concentration in terms of amount of moles of solute in volume solution Moles of solute Molarity = M = Liters of solution

29. Molality m Moles solute m = Kg of solvent • States the number of moles of solute per kilogram of solvent • Different from molarity because it is defined in terms of mass of solvent rather than volume of solution • Does not vary with temperature change because mass does not depend on temp • Molaritydoes vary because volumes change with temperature due to expansion / contraction • Thus..molality is used when solution is to be used over a range of temperatures

30. Conversion of Concentration Units • Sometimes the concentration of a given solution needs to be known in several different concentration units • We can interconvert units • How can we do this..easy! • From Molarity – find moles and volume • From Molality – find mass of solvent / solute • From Mole Fraction – find mole both mole amounts • We can find volume and mass amounts using density

31. Practice Problem • A solution containing equal masses of glycerol, C3H803, and water has a density of 1.10 g/mL. • Calculate: • The molality of glycerol • The mole fraction of glycerol • The molarity of glycerol in solution

32. Colligative Properties and Colloids AP Chemistry

33. Colligative Properties • Colligative properties are properties of solutions that depend on the number of particles in a given volume of solvent and not on the mass of the particles. • Colligative properties include: • lowering of vapor pressure; • elevation of boiling point; • depression of freezing point; • osmotic pressure

34. Vapor Pressure - Recall • Vapor Pressure is the pressure exerted on the outside environment by particles escaping from a liquid • Volatile substances escape readily • Nonvolatile substance do not escape readily • We can lower the vapor pressure of a solvent by adding a nonvolatile solute • The change in V.P. depends on the concentration of the new solution

35. Raoult’s Law • Raoult’s Law says that the vapor pressure of a solution, PA, is proportional to the mole fraction of the solvent, XA. PA° is the vapor pressure of the pure solvent • Just as an ideal gas was one that obeyed the ideal gas law, an ideal solution is one that obeys Raoult's law.

36. Raoult’s Law A nonvolatile solute reduces the rate of vaporization of the solvent XA = mole fraction of solvent PA = V.P. of pure solvent

37. Raoult’s Law Just as an ideal gas was one that obeyed the ideal gas law, an ideal solution is one that obeys Raoult's law.

38. Raoult’s Law Practice Problem • The vapor pressure of pure water at 20°C is 17.5 torr. What is the vapor pressure of water over a solution made by dissolving 50.0 g of glucose (C6H12O6) in 50.0 g of water? A. B. C. D.

39. Effect on Boiling Point • A solution of a nonvolatile solute will boil at a higher temperature than will pure solvent. • Ex: Salting water  boils at a higher temp • Why? • The normal boiling point of a liquid is the temperature at which its vapor pressure is equal to 1 atm pressure • Vapor pressure is depressed by the presence of a solute • So.. in order for the vapor pressure over a solution to equal atmospheric pressure, the temperature will have to be higher

40. Effect on Freezing Point • Freezing point is likewise affected • Addition of a nonvolatile solute will depress the normal freezing point • For example: • Salting the roads during the winter lowers the freezing point of water and turns icy roads into wet roads.)

41. Boiling-Point Elevation and Freezing-Point Depression

42. What Happens When an Electrolyte Dissolves? • When an electrolyte dissolves, it comes apart either by ionization or by dissociation. • The result is more dissolved particles in solution. • Example: 0.100 m solution of sodium chloride, we obtain a solution that is • 0.100 m in sodium ions • 0.100 m in chloride ions • Total molal concentration of dissolved particles is 0.200 m – the freezing point is twice as depressed!

43. The phase diagram for a solution is superimposed on the phase diagram for the pure solvent

44. Freezing Point Depression Practice Problem • What is the freezing point of a solution made by dissolving 25.5 g of glucose (C6H12O6) in 1.00 kg of water? = (1.86) (0.1416) = 0.263 C New F.P. = 0 – 0.263 = -0.263 C m = mole solute / Kg solvent = (25.5g / 180 g/mole) / 1.0 Kg) = 0.1416

45. Boiling Point Elevation Practice problem • What is the change in boiling point (from that of pure water) of an aqueous solution that is 0.115 m in (NH4)2SO4? Kb = 0.52 °C/m

46. Additional Practice with Colligative Properties • Which aqueous solution will have the lowest freezing point?

47. Osmosis • When a semipermeable membrane (one through which solvent can move but solute particles cannot) separates a solution and pure solvent, solvent will flow through the membrane into the solution. This phenomenon is known as osmosis. Pure Solvent Solution

48. Osmosis • Movement through membranes Applied pressure on the left arm of the apparatus stops net movement of solvent from the right side of the semipermeable membrane. This applied pressure is known as the osmotic pressure of the solution.

49. Why is Osmosis Important? • Osmosis is very important biologically. • This Figure shows the effects of osmosis on red blood cells. • Both processes destroy the blood cells. • For red blood cells to be protected, they must be kept in a solution that is isotonic(same molar concentration, same osmotic pressure) with the solution within their cell membranes. • This Process is used in dialysis Hypertonic Solution Hypotonic Solution Crenation Hemolysis • Crenation caused by movement of water from the cell. • (b) Hemolysis caused by movement of water into the cell. **Both processes destroy RBC’s**

50. Dialysis • In a dialysis machine, blood from the patient runs through tubes made of a semi-porous membrane. Outside the tubes is a sterile solution made up of water, sugars and other components. • Red and white blood cells and other important blood components are too large to fit through the pores in the membranes, but urea and salt flow through membranes into the sterile solution and are removed.