1 (84)

Prévia do material em texto

4 Reactions in Aqueous Solution Visualizing Concepts 4.1 Analyze. Correlate the formula of the solute with the charged spheres in the diagrams. Plan. Determine the electrolyte properties of the solute and the relative number of cations, anions, or neutral molecules produced when the solute dissolves. Solve. is a strong electrolyte, a soluble ionic solid that dissociates into separate Li+ and when it dissolves in water. There are twice as many Li+ cations as anions. Diagram (c) represents the aqueous solution of a 2:1 electrolyte. 4.2 Analyze/Plan. Correlate the neutral molecules, cations, and anions in the diagrams with the definitions of strong, weak, and nonelectrolytes. Solve. (a) AX is a nonelectrolyte, because no ions form when the molecules dissolve. (b) AY is a weak electrolyte because a few molecules ionize when they dissolve, but most do not. (c) AZ is a strong electrolyte because all molecules break up into ions when they dissolve. 4.3 Analyze/Plan. From the molecular representations, write molecular formulas for the compounds. Using Table 4.2 and molecular formulas (there are no ionic compounds in this exercise), classify the compounds as strong acid, strong base, weak acid, weak base (NH₃) or nonelectrolyte. Strong acids and bases are strong electrolytes, weak acids and bases are weak electrolytes. Solve. (a) HCOOH. The molecule has a -COOH group; it is a weak acid and weak electrolyte (it is not one of the strong acids listed in Table 4.2). (b) The molecule is a strong acid (Table 4.2) and a strong electrolyte. (c) CH₃CH₂OH. The molecule is neither an acid nor a base; it is a nonelectrolyte. 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 has about the same brightness of 0.001 M HBr, the two solutions have about the same number of ions. Since 0.1 M CH₃COOH has 100 times more solute than 0.001 M HBr, HBr must be dissociated to a much greater extent than CH₃COOH. HBr is one of the few molecular acids that is a strong electrolyte. is a weak electrolyte; if it were a nonelectrolyte, the bulb in Figure 4.2 wouldn't glow. 78