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Solution - a homogeneous mixture of two or more chemical substances

Solution - a homogeneous mixture of two or more chemical substances. Solvent - the major component of a solution ( or sometimes the only liquid component). Solute - a minor component of a solution (the stuff which is dissolved in the solution).

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Solution - a homogeneous mixture of two or more chemical substances

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  1. Solution - a homogeneous mixture of two or more chemical substances Solvent - the major component of a solution ( or sometimes the only liquid component) Solute - a minor component of a solution (the stuff which is dissolved in the solution)

  2. Solutions: Concentration Expressions Molarity: Moles of solute per liter of solution Molality: Moles of solute per Kg of solvent Mole Fraction: Moles of solute divided by total moles of solute and solvent.

  3. Thermodynamics of Solubility What is DH° of solution?

  4. Thermodynamics of Solubility DH° = +3 kJ/mol

  5. So why do salts with DH positive dissolve?

  6. Entropy DG = DH - TDS NaCl DS° = 46 J/Kmol But some DS° values are negative!

  7. Hydration of a salt - MX The higher the charge on the ion and the smaller the size of the ion, the greater the interaction. This leads to a greater ordering of the water.

  8. The solvation of the ions leads to an ordering of the water solution. Thus an decrease in the entropy of the water. Chemical species that interact favorably with water are call hydrophilic. Chemical species that do not interact favorably with water are called hydrophobic.

  9. Non polar molecules such as hexane do not dissolve in water. Oil floats on the top of water. The enthalpy for dissolving hexane in water is actually negative. So why doesn’t it dissolve?

  10. When a non polar molecule is dissolved in water the water molecules form a highly ordered clatharate structure The structure here is a two dimensional representation of the true structure which three dimensional. This ordering of the water molecules leads to a negative DS. This is the basis of the hydrophobic effect

  11. Solubilities of alcohols in water Methanol infinite Ethanol infinite 1-propanol infinite 1-butanol 80 g/L 1-pentanol 22 g/L 1-hexanol 5 g/L

  12. Surfactants

  13. The amount of gas dissolved in a liquid solution is directly proportional to the pressure. Partial Pressure = P = kHC Henry’s Law kH (atm) for water CH4 4.13 x 102 O2 4.34 x 104 N2 8.57 x 104

  14. In the atmosphere how much O2 will dissolve in H2O? P = kHC kH O2 4.34 x 104 atm P(O2) in atm .21atm .21atm = 4.34 x 104 atm x C C = 4.84x 10-6 mol fraction of O2 1000 g H2O/18 g/mol = 55.6 mol H2O 4.84x 10-6 x 55.6 = 2.69 x 10-4 mol O2 2.69 x 10-4 mol x32 g/mol= .0086 gO2

  15. .0086 gO2 / liter H2O at normal atmospheric pressure In the actual atmosphere .21 x 32.0 g / 22.4 = .30 g O2 / liter air Aren’t you glad you are not a fish!

  16. What will happen if you have two beakers in a closed system? One contains 1 liter of 1M NaCl, the other 1 liter of pure H2O.

  17. Raoult’s Law Vapor pressure of solution with a nonvolatile solute. Pobs = CsolvPosolv

  18. Raoult’s Law for a mixture of two volatile liquids. Ptotal = PA + PB = CAPoA + CBPoB

  19. Raoult’s says that the presence of a solute will lower the vapor pressure of a solution as compared to the pure solvent. What will this do to the freezing point and boiling point of the solution?

  20. Freezing Point Depression DT = Kf msolute Boiling Point Elevation DT = Kb msolute

  21. Calculate the boiling point of a solution containing 6.16 g of sucrose, C12H22O11, dissolved in 30.g of H2O. DT = Kb msolute Kb = 0.51 C°kg/mol m.wt. sucrose 342 g/mol mol = 6.16 g/(342g/mol) = .018 mol m = .018 mol / .030 kg = .60 mol/kg DT = 0.51 C°kg/mol x .60 mol/kg =.31 C° Boiling point of solution = 100.31 C°

  22. A solution of .90g of glucose in 20.0g of water hasa freezing point of -0.465 C°. What is mwt. of glucose? Kf = 1.86 C°kg/mol m = DT/Kf = .465 C° / (1.86 C°kg/mol) =.25 m .25 mol/kg = X mol/.020kg X mol of glucose = .005 mol .90 g/ .005 mol = mwt. / 1mol = 180 g / mol

  23. Osmosis Osmotic Pressure is the pressure that just stops the osmosis. p = MRT

  24. p = MRT

  25. A 2.2 gram sample of polyethylene was disolved in toluene to give 100ml solution. The osmotic pressure at 25°C was measured to be 1.10 x 10-2atm. What is the mwt. of the polyethylene? p = MRT M = p / RT M = 1.10 x 10-2 / (.082 x 298) = 4.5 x 10-4 M .10 L x 4.5 x 10-4 mol/L = 4.5 x 10-5 mol 2.2 g / 4.5 x 10-5 mol = mwt = 49,000 g/mol 49,000/ 28 = 1750 units

  26. Reverse Osmosis

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