The solubility of gases in water usually decreases with temperature (see Table 11.2, page 611), for example:

1. The solubility of gases in water usually decreases with temperature (see Table 11.2, page 611), for example:

3. The gases in air are not very soluble in water under ordinary pressure • The solubility increases as the pressure is increased The amount of gas that dissolves in water increases as the pressure is raised.

4. How an increase in pressure increases the solubility of a gas in a liquid. (a) At some specific pressure, an equilibrium exists between the vapor phase and the solution. (b) An increase in pressure puts stress on the equilibrium. More gas molecules dissolve than are leaving the solution. (c) More gas has dissolved and equilibrium has been restored.

6. Got “the Bends”?

9. For gases that do not react with the solvent, Henry’s law or the pressure-solubility law applies: The concentration of a gas in a liquid at any given temperature is directly proportional to the partial pressure of the gas over the solution

10. The solubility of O2(g) at 25 degree Celsius is 8.2 mg/L when the partial pressure is 152 torr.What is the solubility of this gas at 25 degrees Celsiuswhen the partial pressure is 800 torr?

11. Gas molecules with polar bonds are much more soluble in water than nonpolar molecules like oxygen and nitrogen • Some gases have increased solubility because they react with water • For example: Carbonic acid bicarbonate

13. Molar concentration or molarity, mol/L, is convenient for the stoichiometry of chemical reactions in solutions • Two other temperature-intensive concentrations are common: • Percent Concentrations • Also called percent by mass or percent by weight • This is sometimes indicated %(w/w) where “w” stands for weight

14. The “(w/w)” is often omitted • Concentrations are sometimes reported as percent by mass/volume of “%(w/v)” • Percentages are parts per hundred (pph) • Other concentrations include parts per million (ppm) and parts per billion (ppb) • 1 ppm = 1 g component in 106 g mixture • 1 ppb = 1 g component in 109 g mixture

15. w/w problem You analyzed 5 grams of apple sauce (“the solution”) and Found it contained 0.3 mg of DDT (“the solute”), a pesticide. Express the concentration of DDT in apple sauce in: Percent (pph)ppt ppmppb

16. w/v problem You analyzed 10 mL of blood (“the solution”) and found it contained 16.0 μg of hemoglobin (“the solute”) Express the concentration of hemoglobin in blood in (this is just an example…not the true concentration of hemo in blood!): Percent (pph)ppt ppmppb

17. The number of moles of solute per kilogram solvent is called the molal concentration or molality (m) • Don’t confuse molality and molarity

18. You need to make a 0.300 molal (m) solution of sodium chloride. How many grams of NaCl would have to be dissolved in 1600.0 g of water to prepare the solution of this molality?

19. A certain sample of dilute hydrochloric acid, HCl, is 5.0% (notice, the w/w or w/v has been omitted…so when in doubt, assume w/w). Calculate the molality of this solution.

20. With water as the solvent, the molality approaches the molarity as the solution becomes more dilute • Colligative properties depend mostly on the relative populations of particles in mixtures, not on their chemical identities • Solutes that can’t evaporate from solution are called nonvolatile solutes • All solutions of nonvolatile solutes have lower vapor pressures than their pure solvents

22. For dilute solution, Raoult’s law applies: • The change in vapor pressure can be expressed as

23. Raoult’s law plot. When the vapor pressure of a solution is plotted against the mole fraction of solvent, the result is a straight line. (a) With a high number of solvent molecules, the rate of evaporation and condensation is relatively high. (b) When some of the solvent is replaced by a nonvolatile solute, the rate of evaporation and the vapor pressure decrease.

24. At 25ºC, the vapor pressure of water is 23.8 torr.What is the vapor pressure of a solution prepared bydissolving 65.0 g of C6H12O6 (a non-volative solute)in 150 g of H2O?

25. When a solution is made from two components that can evaporate, the vapor contains molecules of each component • Each component is described by Raoult’s law, using the labels A and B:

26. For an ideal, two-component solution of volatile components: The vapor pressure of an ideal, two-component solution of volatile components (A and B).

27. Solutes affect the boiling and freezing point of solutions (relative to the pure solvent) Phase diagrams for water and an aqueous solution (not to scale). (a) Phase diagram for pure water. (b) Phase diagram for an aqueous solution of a nonvolatile solute.

28. The increase in boiling point is called the boiling point elevation • The decrease in freezing point is called the freezing point depression • Simple expressions relate the molality (m) to the temperature change:

29. Table 14.3 (page 624) lists a number of boiling point elevation and freezing point depression constants • These include: