PROPERTIES OF SOLUTIONS

Solution Composition

Concentration Term Ratio

Molarity (M) mol of soluteliter of solution

Molality (m) mol of solutekg of solvent

Mass percent (%) mass (g) of solutemass (g) of solution

x 100

Mole fraction of A (χA) mol of Amoles of all components

Normality (N) equivalent of soluteliter of solution

1. Determine the percent by mass of KCI in a solution prepared by dissolving 1.18 g of KCl in 86.3 g of water.

2. What is the molality of a solution prepared by dissolving 6.44 g of naphthalene (C10H8) in 80.1 g benzene (C6H6)?

3. What is the mole fraction of CO2 in a mixture of 0.756 mole of N2, 0.189 mole of O2 and 0.0132 mole of CO2?

4. Toluene (C6H5CH3), an organic compound often used as a solvent in paints, is mixed with a similar organic compound, benzene (C6H6). Calculate the molarity, molality, mass percent and mole fraction of toluene in 200. mL of solution that contains 75.8 g of toluene and 95.6 g of benzene. The density of the solution is 0.857 g/mL. [MM toluene = 92.14 g/mol; MM benzene = 78.11 g/mol]

5. At 20.0°C, a 0.258 m aqueous solution of glucose (C6H12O6) has a density of 1.0173 g/mL. Calculate the molarity of this solution.

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The Energies of Solution Formation

We can imagine the solution process taking place in the three distinct steps:Step 1 is the separation of solute molecules.Step 2 is the separation of solvent molecules.In step 3 the solvent and solute molecules mix.

As a rule of thumb, like dissolves like.

1. Determine for each solute whether the solubility will be greater in water or in benzene (C6H6):(a) bromine (Br2), (b) sodium iodide (Nal), (c) carbon tetrachloride (CCI4), and (d) formaldehyde (CH2O).

2. Predict whether each vitamin will be water soluble or fat soluble. (In general, fats are nonpolar molecules containing hydrocarbon chains).

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Factors Affecting Solubility

1. Calculate the concentration of CO2 in a soft drink that was bottled under a partial pressure of 5.0 atm CO2 at 25°C (a) before the bottle is opened and (b) after the soda has gone 'flat' at 25°C. The Henry's law constant for CO2 in water at this temperature is 3.1 x 10−2 mol/L.atm. Assume that the partial pressure of CO2 in air is 0.0003 atm and that the Henry's law constant for the soft drink is the same as that for water.

2. At 20°C the solubility of N2 in water is 0.0150 g/L when the partial pressure of N2 is 580 torr. What will be the solubility of N2 in water at 20°C when its partial pressure is 800 torr?

Colligative Properties

Colligative Property Equation

Vapour Pressure Lowering Psolution = χsolvent P°solvent

Boiling Point Elevation ΔT = i kb msolute

Freezing Point Depression ΔT = i kf msolute

Osmotic Pressure Π = i MRT

1. Carbon tetrachloride has a vapor pressure of 100 torr at 23°C. Considering that candle wax is essentially nonvolatile with a molecular formula C22H46 (MM = 311 g/mol), what is the vapor pressure at 23°C of a solution prepared by dissolving 10.0 g of wax in 40.0 g CCl 4 (MM = 154 g/mol)?

2. What is the vapor pressure of a solution made by adding 52.9 g CuCl2 to 800.0 mL of H2O at 52.0°C. The vapor pressure of H2O at 52°C is 102.1 torr and the density of H2O at 52°C is 0.987 g/mL. [MM (H2O) = 18.01 g/mol; MM (CuCl2) = 134.5 g/mol]

3. At 29.6°C pure water has a vapor pressure of 31.1 torr. A solution is prepared by adding 86.7 g of Y (nonvolatile, nonelectrolyte solute) to 350.0 g H2O. The vapor pressure of the resulting solution is 28.6 torr. Calculate the molar mass of Y.

4. The vapor pressure of pure hexane at 60°C is 573 torr. The vapor pressure of benzene at 60°C is 391 torr. What is the expected vapor pressure of the solution prepared by mixing 58.9 g of hexane (MM = 86.0 g/mol) with 44.0 g benzene (MM = 78.0 g/mol), assuming ideal solution.

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5. The vapor pressure of pure hexane and pentane at 25°C are 149.1 torr and 508.5 torr, respectively. A solution is prepared in which the mole fraction of hexane is 0.750.(a) What are the vapor pressures of hexane and pentane above the solution?(b) What is the mole fraction of each substance in the vapor phase?

6. A solution is prepared by adding 31.65 g of sodium chloride to 220.0 mL of H2O at 34.0°C. The density of water is 0.994 g/mL and Kb for H2O is 0.51°C·Kg/mol. Calculate the boiling point of the solution, assuming complete dissociation of NaCl in solution. [MM (NaCl) = 58.44 g/mol]

7. How many grams of glycerine (C3H8O3) must be added to 350.0 g of water, in order to lower the freezing point to –3.84°C? [Kf for water = 1.86°C.·Kg/mol and MM (C3H8O3) = 92.1 g/mol]

8. A chemist is trying to identify a human hormone by determining its molar mass. A sample weighing 0.546 g was dissolved in 15.0 g benzene and the freezing point depression was found to be 0.240°C. Calculate the molar mass of the hormone. [Kf (benzene) = 5.12°C·Kg/mol]

9. The osmotic pressure of a solution containing 26.5 mg of aspartame per liter is 1.70 torr at 30°C. Calculate the molar mass of aspartame. [1 atm = 760 torr, R = 0.08206 L·atm/K·mol]

10. Calculate (a) the observed freezing point of a 0.050 m FeCl3 solution and (b) the osmotic pressure of the same solution at 25.0°C, assuming that the molarity is 0.050 M. Kf for H2O is 1.86°C·Kg/mol and i is 3.4.

11. The observed osmotic pressure for a 0.10 M solution of Fe(NH4)2(SO4)2 at 25°C is 10.8 atm. What would be the expected and experimental value for i? [R = 0.08206 L·atm/mol·K]

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