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Unformatted text preview: 4 Aqueous Reactions and Solution Stoichiometry Visualizing Concepts 4.2 Although CH 3 OH and HCl are both molecular compounds, HCl is an acid and strong electrolyte. Strong electrolytes exist in solution almost completely as ions, so an aqueous HCl solution conducts electricity. CH 3 OH is a nonelectrolyte that exists as neutral molecules in aqueous solution. Since there are no charge carriers, aqueous solutions of nonelectrolytes such as CH 3 OH do not conduct electricity. 4.4 The brightness of the bulb in Figure 4.2 is related to the number of ions per unit volume of solution. If 0.1 M HC 2 H 3 O 2 has about the same brightness of 0.001 M HBr, the two solutions have about the same number of ions. Since 0.1 M HC 2 H 3 O 2 has 100 times more solute than 0.001 M HBr, HBr must be dissociated to a much greater extent than HC 2 H 3 O 2 . HBr is one of the few molecular acids that is a strong electrolyte. HC 2 H 3 O 2 is a weak electrolyte; if it were a nonelectrolyte, the bulb in Figure 4.2 wouldn’t glow. 4.6 Certain pairs of ions form precipitates because their attraction is so strong that they cannot be surrounded and separated by solvent molecules. That is, the attraction between solute particles is greater than the stabilization offered by interaction of individual ions with solvent molecules. 4.8 Use the difference in reactivities with SO 4 2 – to identify Pb 2 + (aq) and Mg 2 + (aq). Test a portion of each solution with H 2 SO 4 (aq). Pb 2 + (aq) is an exception to the soluble sulfates rule, so Pb(NO 3 ) 2 (aq) will form a precipitate, while Mg(NO 3 ) 2 (aq) will not. 4.10 Diagram I shows spectator ions but no precipitate; this corresponds to reaction (b). Diagram II shows spectator ions and a 1:1 precipitate; this corresponds to reaction (c). Diagram III shows only precipitate; this corresponds to reaction (a). The second product in reaction (a) is H 2 O(l), which is also the solvent. Solvent molecules are not shown in any of the diagrams. Electrolytes 4.12 When CH 3 OH dissolves, neutral CH 3 OH molecules are dispersed throughout the solution. These electrically neutral particles do not carry charge and the solution is nonconducting. When HC 2 H 3 O 2 dissolves, mostly neutral molecules are dispersed throughout the solution. A few of the dissolved molecules ionize to form H + (aq) and C 2 H 3 O 2 – (aq). These few ions carry some charge and the solution is weakly conducting....
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