Chapter 11. Suggested problems: 5, 9, 13, 15, 31, 33, 37, 39, 41, 43, 45, 53

Transcription

1 Suggested problems: 5, 9, 13, 15, 31, 33, 37, 39, 41, 43, 45, 53

2 Solutions Solution solvent & solute. Solution homogenous mixture single phase.

3 Types of solutions All nine combinations are possible: Solute Solvent Gas Gas Gas Liquid Gas Solid Liquid Gas Liquid Liquid Liquid Solid Solid Gas Solid Liquid Solid Solid

4 Effect of temperature on solubility If dissolving solute is exothermic then increase in temperature makes solute less soluble If dissolving process is endothermic increasing temperature will make solute more soluble. Dissolving ionic solid is usually endothermic (takes energy to break up lattice) and so most ionic solids are more soluble with increasing temperature.

5 Dissolving a solid in a liquid is a three-step process. 1) Breaking the bonds between the solid particles - that takes energy - endothermic 2) Breaking the bonds between the liquid molecules to make room for the solid particles - that takes energy - endothermic 3) Making bonds between the solute and solvent particles - that releases energy - exothermic

6 When a solute is soluble, steps 1 and 2 require less energy than step three produces. When a solute is insoluble, the first two steps require too much energy. Usually, it is the first step - breaking the forces between solute particles - requires too much energy.

7 NaCl is soluble in water because step 3, where the Na + and Cl - ions bind to the water molecules, releases sufficent energy.

8 Chapter 10 ion-dipole. Na + H O δ+ δ- H

9 Hydration of NaCl(aq) NaCl(aq) Na + (aq) + Cl - Na Cl Na + O Cl - H H

10 Oil won t dissolve in water because, though the oil molecules are easily separated (step 1), there is no real attraction for the oil molecules for the water molecules (step 3).

11 Gases less soluble in liquids with increasing temperature. Increasing temp increases molecular vibrations Decreases intermolecular forces.

12 Gas-Liquid solutions Henry's law As the (partial) pressure of a gas is increased above the liquid, the solubility of the gas goes up. Carbonated beverages

13 Solutions Unsaturated: less solute dissolved than possible Saturated: Maximum amount of solute dissolved Supersaturated: More solute dissolved than is supposed to dissolve.

14 Molarity M = mols of solute volume solution % by weight (w/w) mass solute mass solution % by volume (v/v) volume solute vol. solute + vol. solvent

15 molality mole fraction m = mols solute Kg of solvent For a solution of A and B χ A = mols A mols A + mols B χ B = mols B mols A + mols B

16 Chaper 11 Calculate the wt of HCl in 5.00 ml of conc HCl solution, of density = 1.19 g/ml and 37.23% HCl (w/w)

17 What is the M of H 2 SO 4 solution, which has a density of 1.2 g/ml and is 27% (w/w)?

18 What is M of 16 g of CH 3 OH in 200 ml soln? M = mols solute/l solution

19 Find the M, m, and χ acid and χ water of a solution of H 2 SO 4 of density = 1.2 g/ml and 27.0% (w/w)

20 b) 1200 g solution minus 324 g H 2 SO 4 = 876 g water

21 c) Mol Fraction: Chapter 11

22 Find the M, m, and χ solute and χ water of a solution of C 6 H 12 O 6 of density = 2.45 g/ml and 34.5% (w/w)

23 b) 2450 g solution minus g C 6 H 12 O 6 = g water

24 c) Mol Fraction: Chapter 11

25 Those properties that depend on the number, but not the nature, of the solute particles Raoult's Law. P. 625 Accounts for vapor pressure lowering. P soln = (χ solvent )(P o pure solvent)

26 Pure solvent Solution

27 The vapor pressure of water at 28 o C is Torr. Find the vapor pressure of a solution of 68 g of C 12 H 22 O 11 in 1000 g of water at 28 o C.

28 B.P. lowering and F.P. elevation 760 ΔT f ΔT b

29 ΔT b = k b m and ΔT f = k f m Calculate the F.P. and B.P. of 2.60 g of urea, CO(NH 2 ) 2 in 50 g of water.

30 Find the F.P. of 900 g ethylene glycol in 6 L water? Given: k f (H 2 O) = 1.86 o C/m Ethylene glycol is (HO)CH 2 -CH 2 (OH)

31 4.50 g of solute is dissolved in 125 g of water. The solution freezes at o C. What is the MW of the solute?

32 What is the MW of a solute if a solution of g solute dissolved in 25 g of benzene has a F.P. = 2.32 o C?

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34 Water moving from higher concentration (of water) to lower concentration of water. Semi-permeable membrane

35 ΠV = nrt or Π = MRT big city Because M = mols/v Π is osmotic pressure Ocean pressure > Π

36 Electrolyte Solutions Colligative properties depend upon the number of particles and not their nature So, ΔT = km is actually: ΔT = ikm where i is: actual number of particles after dissolution number of formula units initally dissolved Book calls i the van t Hoff factor (p. 513)

37 Electrolyte Solutions Calculate the freezing point of 62 g of H 2 SO 4 in 500 g of water Remember, H 2 SO 4 --> 2 H + + SO 4 2-

38 Electrolyte Solutions i actually usually less than the ideal value Due to formation of ion pairs That is, when ionic material dissolves Some cations and anions don t separate Especially true when cation and anion have high charge to size ratios Al 2 (SO 4 ) 3 --> Al 3+ + SO > Al SO 4 2-

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