Química Ambiental Exercícios

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18 Chemistry of the Environment Solutions to Exercises Check. The largest numbers in the molarity sum have 2 decimal places, so has 2 decimal places and 3 sig figs. AM also has 2 decimal places and 3 sig figs so the calculated pressure has 3 sig figs. Units are correct. 18.45 Analyze/Plan. Under aerobic conditions, excess oxygen is present and decomposition leads to oxidized products, the element in its maximum oxidation state combined with oxygen. Under anaerobic conditions, little or no oxygen is present so decomposition leads to reduced products, the element in its minimum oxidation state combined with hydrogen. Solve. (a) (b) 18.46 (a) Decomposition of organic matter by aerobic bacteria depletes dissolved A low dissolved oxygen concentration indicates the presence of organic pollutants. (b) According to Section 13.3, the solubility of O₂(g) (or any gas) in water decreases with increasing temperature. 18.47 Analyze/Plan. Given the balanced equation, calculate the amount of one reactant required to react exactly with a certain amount of the other reactants. Solve the stoichiometry problem. g mol mol ratio mol O₂ g Solve. Notice that the mass of O₂ required is 2.5 times greater than the mass of biodegradable material. 18.48 1,200,000 persons 1 person = = x10¹⁰ 18.49 Analyze/Plan. Slaked lime is Ca(OH)₂(s). The reaction is metathesis. Solve. + Ca(OH)₂(s) Mg(OH)₂(s) + The excess is removed as CaCO₃ by naturally occurring bicarbonate or added Na₂CO₃. 18.50 (a) Mg²⁺, (b) Divalent cations (ions with 2+ charges) contribute to water hardness. These ions react with soap to form scum on surfaces or leave undesirable deposits on surfaces, particularly inside pipes, upon heating. 18.51 Analyze/Plan. Given [Ca²⁺] and [HCO₃⁻] calculate mole Ca(OH)₂ and Na₂CO₃ needed to remove the Ca²⁺ and Consider the chemical equations and reaction stoichiometry in the stepwise process. Solve. Ca(OH)₂ is added to remove as CaCO₃(s), and Na₂CO₃ removes the remaining Ca²⁺. Ca + (aq) + + One mole Ca(OH)₂ is needed for each 2 moles of (aq) present. 560