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chapter15

# chapter15 - 688 Chapter 15 The Chemistry of Solutes and...

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Chapter 15: The Chemistry of Solutes and Solutions 688 End-of-Chapter Solutions for Chapter 15 Summary Problem Answer: Mixture I (a) 20.0% CCl 4 , 80% H 2 O (b) 0.200 CCl 4 , 0.800 H 2 O (c) No, CCl 4 does not dissolve in water. (d)-(j) N/A; Mixture II (a) 10.7% CaCl 2 , 89.3% H 2 O (b) 0.107 CaCl 2 , 0.893 H 2 O (c) Yes, CaCl 2 dissolve and ionizes in water. (d) Aqueous calcium ions and chloride ions, see sketch below (e) 107,000 ppm (f) 1.08 M (g) 22.45 mm Hg (h) 101.7 °C (i) –6.03 °C (j) 79.3 atm; Mixture III (a) 1.2% HOCH 2 CH 2 OH, 98.8% H 2 O (b) 0.012 HOCH 2 CH 2 OH, 0.988 H 2 O (c) Yes, HOCH 2 CH 2 OH dissolve in water. (d) Aqueous ethylene glycol, see sketch below (e) 120,000 ppm (f) 2.3 M (g) 18.7 mm Hg (h) 101.2 °C (i) –4.3 °C (j) 56 atm Strategy and Explanation: Three mixtures are given. Given the mass of substance and a given volume of water, calculate the weight percent, mass fraction, and determine if a solution is formed. If a solution is formed, name the dissolved species, draw a diagram representing how the solvent molecules interact with them, find the concentration in units of ppm and molarity, calculate the boiling point, freezing point, and osmotic pressure of the solution. (a) Weight percent, also known as percent by mass, is calculated by determining the mass of each substance in the mixture, determining the total mass, calculating the mass fraction, then multiply by 100%. The sum of the percentages must equal 100%. (The density of water at 25°C is 0.997 g/mL, given in Chapter 2, Question 118, page 77.) (b) Mass fraction is calculated during part (a). The sum of the mass fractions must equal1. (c) A solution is formed if the substances added to the water dissolves. Determine the intermolecular forces experienced by each substance. If they have common interactions, then they will be miscible and form a solution. H 2 O is polar, since the terminal atoms are not symmetrically arranged around the O atom: .. . . H O H The presence of an O–H bond in asymmetrical water molecules also means that water molecules can also experience hydrogen boding intermolecular forces. If the solute is non-polar, then it will be immiscible in water. Only do (d)-(j), if a solution forms. (d) Names of ions and compounds are described in Chapter 3. Draw representation of how the water molecules interact with the dissolved ions and molecules. (e) Parts per million (ppm) is usually by mass (see Section 15.6, page 738). We can calculate the mg of solute and the kg of solution, and calculate the ratio, or we could just take the mass fraction, which is “parts per 1” (calculated in (b)) and multiply by one million, 1,000,000. (f) Molarity is calculated by determining the moles of solute divided by the volume of solution in liters. For dilute solutions, assume that the volume of solute is the volume of the solution. (g) To get the vapor pressure of water in equilibrium, use Raoult’s law, described in Section 15.7. P 1 = X 1 P 1 0 Where P 1 is the vapor pressure over the solution, P 1 0 is the vapor pressure over the pure solvent, and X 1 is the mole fraction of the solvent (described in Section 10.8). X 1 = n solvent n tot (h) To get the boiling point of the solution, use the method described in Section 15.7.

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chapter15 - 688 Chapter 15 The Chemistry of Solutes and...

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