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Physical Properties of Solutions

Physical Properties of Solutions. Chapter 13. Factors Affecting Solubility. Fig 13.12 Structure and solubility. Glucose (which has hydrogen bonding) is very soluble in water Cyclohexane (which only has dispersion forces) is not. Pressure Effect on Gases in Solution.

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Physical Properties of Solutions

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  1. Physical Properties of Solutions Chapter 13

  2. Factors Affecting Solubility Fig 13.12 Structure and solubility • Glucose (which has hydrogen bonding) is very soluble in water • Cyclohexane (which only has dispersion forces) is not

  3. Pressure Effect on Gases in Solution • Solubility of liquids and solids does not change appreciably with pressure • Solubility of a gas in a liquid is directly proportional to its pressure Fig 13.14 Effect of pressure on gas solubility

  4. Henry’s Law Fig 13.15 Solubility decreases as pressure decreases Sg = kPg where • Sg ≡ solubility of the gas • k ≡ the Henry’s Law constant for that gas in that solvent • Pg ≡ partial pressure of the gas above the liquid

  5. Temperature Effect on Solids and Liquids Fig 13.17 Solubilities of several ion compounds as a function of temperature • Generally, the solubility of solid solutes in liquid solvents increases with increasing temperature

  6. Temperature Effect on Gases Fig 13.18 Variation of gas solubility with temperature • The opposite is true of gases: • Carbonated soft drinks are more “bubbly” if stored in the refrigerator • Warm lakes have less O2 dissolved in them than cool lakes

  7. Concentration Units Concentration - amount of solute present in a given quantity of solvent or solution: • Mass percentage • Mole fraction • ppm and ppb • Molarity • Molality

  8. moles of A XA = sum of moles of all components x 100% mass of solute x 100% (w/w) = mass of solution mass of solute mass of solute + mass of solvent Concentration Units Mass percentage (w/w) % by mass = Mole Fraction(X)

  9. Practice Exercise p 543 • Calculate the mass percentage of NaCl in a solution containing 1.50 g of NaCl in 50.0 g of water. • (b) A commercial bleaching solution contains 3.62 mass % sodium hypochlorite, NaOCl. What is the mass of NaOCl in a bottle containing 2.50 kg of bleaching solution? • Answer: (a) 2.91% • (b) 90.5 g of NaOCl

  10. Sample Exercise 13.6 Calculation of Mole Fraction An aqueous solution of hydrochloric acid contains 36% HCl by mass. Calculate the mole fraction of HCl in the solution. Assume we have 100. g of solution:

  11. Parts per million (ppm) Parts per billion (ppb) Concentration Units Continued

  12. moles of solute liters of solution moles of solute m = mass of solvent (kg) M = Concentration Units Continued Molarity(M) Molality(m)

  13. Practice Exercise p 544 What is the molality of a solution made by dissolving 36.5 g of naphthalene (C10H8) in 425 g of toluene (C7H8)? Answer: 0.670 m

  14. Conversion of Concentration Units Fig 13.19 Calculating molality and molarity • If we know the density of the solution, we can calculate the molality from the molarity and vice versa.

  15. moles of solute moles of solute m= m= moles of solute M = mass of solvent (kg) mass of solvent (kg) liters of solution 5.86 moles C2H5OH = 0.657 kg solvent What is the molality of a 5.86 M ethanol (C2H5OH) solution whose density is 0.927 g/mL? • Assume 1 L of solution: • 5.86 moles ethanol = 270 g ethanol • 927 g of solution (1000 mL) (0.927 g/mL) mass of solvent = mass of solution – mass of solute = 927 g – 270 g = 657 g = 0.657 kg = 8.92 m

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