Properties of Solutions

1. Properties of Solutions

2. Solutions • Saturated • Unsaturated • Supersaturated • (Demo sodium acetate)

3. Solution Concentration • A 10.7 m soln of NaOH has d = 1.33 g/cm3. Calc. • a) mole fraction of NaOH • b) the weight % of NaOH • c) the M of the soln

4. answers • a) 0.161 • b) 30.0% NaOH • c) 9.98 M

5. Temperature and Solubility • If delta H is positive (endothermic) • If delta H is negative (exothermic)

6. Energy Changes in the Solution Process (slide 264 + 265) • Three steps in the solution process • 1)solute particles are separated • delta H1 = positive • 2) solvent particles are separated • delta H2 = positive • 3) solvent and solute mix • delta H3 = negative

7. Heat of solution = H1 + H2 + H3 • If H3> H1 +H2 the soln is exothermic - solute dissolves and solution warms • If H3< H1 +H2 the soln is endo - solute dissolves and soln cools • If H3<<< H1 +H2 the solute may not dissolve

8. Ionic Solutes - heat of hydration • Process same as last slide • Hsoln = Hsolute + Hhydration • Ion size and charge determines hydration energy - charge density

9. Which has the higher charge density? • a) Na+ or Cs+ b) Sr2+ or Rb+ • Which has the larger Hhydration? • a) Mg2+ or Ba2+ b) Mg2+ or Na+ • What generalization can we make about size, charge and solubility?

10. NH4Cl diss. in water - endothermic • a) is Hlattice for NH4Cl larger than Hhydration?? • ans: lattice must be > hydration • b) Given the answer to a) why does the solution form?? • ans: entropy

11. Factors Affecting Solubility • Molecular Structure - list generalizations • Ex. polar sub. dissolve polar

12. which of the following will result in a more concentrated solution Explain • KNO3 in water or KNO3 in CCl4?

13. Factors Affecting Solubility • Gas Pressure - Henry’s Law - • Sgas = KH x Pgas • Ex. degasing chlorine

14. The PP of CO2 inside a soda btl. is adjusted to 4 atm. What is the solubility of CO2? KH CO2 = 3 x 10-2 mol/L*Atm • ans: 0.1 mol/liter

15. Colligative PropertiesVapor Pressure of Solns • Raoult’s Law • VPsoln = Xsolvent x VPsolvent • X = mole fraction

16. Calculate the Vapor Pressure when 0.137 mol of glycerol (C3H8O3,MM = 92 amu) is added to 27.4 mol of water at 50 C. (VP of water at this T is 92.5 torr).

17. Problem Solution • mole fraction of solvent = • 27.4 mol H2O = 0.995 • 27.4 + 0.137 mol glycerol • VP = 92.5 torr x 0.995 = 92.0 torr

18. Colligative Properties • boiling point elevation(phase diagram) • freezing point depression • delta T = Kbmi kb = 0.512 C • delta T = Kfmi Kf = 1.86 C

19. Boiling Point Elevation • If 1.00 kg of antifreeze (MM = 62.07 - non volatile, non dissociating) is added to 4450 g of water what is the boiling point of the solution?

20. Problem Solution • mole of antifreeze = • 1.00 x 10 3 g/62.07 = 16.1 mol • molality = 16.1 mol/ 4.450 kg solvent • = 3.62

21. molality problem solution • Tb = Kb x molality x i • = 0.512 C/m x 3.62 m = 1.85 C • Therefore BP = 101.85 C

22. Collig. Prop. MM calc • 1 mol of napthalene is diss. in 1000 g of benzene - the FP changes from 5.51C to 0.41 C. When 20. g of an unkwn is diss. in 500 g benzene the Fp of soln is 5.00C. What is the MM of the unkwn. (Hint: find Kf for benzene and appl. to unknown)

23. Answer • Kf(benz) --> Tf = m x Kfxi • 5.1 C = 1 m x Kf Kf = 5.1 C/m • then for unknown • 0.51 C = X (5.1C/m) X = 0.1 mol/Kg • next • 0.1 mol/kg (0.5kg)=0.05 mol unknown

24. ans cont’d • finally • 20g unknown/0.05 mol = 400 g/mol

25. Colligative Properties • antifreeze • making ice cream • salt on the streets

26. Lab: Let’s make Ice Cream

27. Osmotic Pressure • Pressure = MRTi • Isotonic solutions (IV drip) • Killing slugs(the idea here (which most north carolinians can relate to) is that you can either put salt on them or put them in water. Either way their death is related to the osmotic flow of water in or out of the cell).