Passage
Copper plays a vital role as a trace mineral for biological processes. The amount of dietary copper needed by an adult each day is about 30 μg/kg of body weight, and blood plasma normally has a copper concentration of 1 mg/L.Copper is an essential element, and toxic effects are not common. However, given sufficient exposure to high levels by inhalation, absorption, or ingestion from sources such as industrial hazards or contaminated groundwater, copper toxicity can occur.Salts that are more soluble tend to exhibit higher toxicity when ingested, but the solubilities of copper salts vary and are also temperature-dependent, as shown by selected examples in Figure 1.
Figure 1 The solubility of selected copper salts in distilled water with increasing temperatureSome copper salts have solubilities much lower than those shown in Figure 1. For example, CuF₂ has a solubility of only 0.075 g per 100 g of water (at 25 °C) . This indicates that CuF₂ dissociates in water only to a small extent (Reaction 1) and that the equilibrium favors the undissociated salt, giving CuF₂ a solubility product constant of K_sp = 1.6 × 10⁻⁶.
Reaction 1Compound-specific properties can also impact solubility. In CuF₂, the dissociated F⁻ ion is mildly basic (pK_b = 10.8) , causing the equilibrium to be influenced by the pH of the solution.Specific characteristics of copper can also play a role. For example, copper ions in solution express an affinity to form coordinate bonds with available lone-pair electrons of nitrogen atoms in amines (Reaction 2) .
Reaction 2If excess amine ligands are present, coordinate bonds like that shown in Reaction 2 will continue to form until each Cu²⁺ ion in solution is coordinated with four nitrogen atoms. This acquisition of copper ions by ligands in solution can also impact the solubility equilibrium of copper salts by forming soluble coordination complexes.
-Based on the passage, which of the following procedures would assist in separating an aqueous mixture of CuCl₂ and CuSO₄ salts at 90 °C?Add Cu(NO₃) ₂ to the solution mixtureAdd Na₂SO₄ to the solution mixtureCool the solution mixture to 5°CLower the pH of the mixture

Question

Passage
Copper plays a vital role as a trace mineral for biological processes. The amount of dietary copper needed by an adult each day is about 30 μg/kg of body weight, and blood plasma normally has a copper concentration of 1 mg/L.Copper is an essential element, and toxic effects are not common. However, given sufficient exposure to high levels by inhalation, absorption, or ingestion from sources such as industrial hazards or contaminated groundwater, copper toxicity can occur.Salts that are more soluble tend to exhibit higher toxicity when ingested, but the solubilities of copper salts vary and are also temperature-dependent, as shown by selected examples in Figure 1.

Figure 1 The solubility of selected copper salts in distilled water with increasing temperatureSome copper salts have solubilities much lower than those shown in Figure 1. For example, CuF₂ has a solubility of only 0.075 g per 100 g of water (at 25 °C) . This indicates that CuF₂ dissociates in water only to a small extent (Reaction 1) and that the equilibrium favors the undissociated salt, giving CuF₂ a solubility product constant of K_sp = 1.6 × 10⁻⁶.

Reaction 1Compound-specific properties can also impact solubility. In CuF₂, the dissociated F⁻ ion is mildly basic (pK_b = 10.8) , causing the equilibrium to be influenced by the pH of the solution.Specific characteristics of copper can also play a role. For example, copper ions in solution express an affinity to form coordinate bonds with available lone-pair electrons of nitrogen atoms in amines (Reaction 2) .

Reaction 2If excess amine ligands are present, coordinate bonds like that shown in Reaction 2 will continue to form until each Cu²⁺ ion in solution is coordinated with four nitrogen atoms. This acquisition of copper ions by ligands in solution can also impact the solubility equilibrium of copper salts by forming soluble coordination complexes.
-Based on the passage, which of the following procedures would assist in separating an aqueous mixture of CuCl₂ and CuSO₄ salts at 90 °C?Add Cu(NO₃) ₂ to the solution mixtureAdd Na₂SO₄ to the solution mixtureCool the solution mixture to 5°CLower the pH of the mixture

Quizplus · Accepted Answer

11ecba2d_120b_f21f_a3bf_db5e1663ac16_MD0008_00 When an ionic compound is placed in water, the composite ions will dissociate to some extent into the solution and establish an equilibrium. The solubility product constant K_sp of the equilibrium provides a measure of the solubility. The K_sp is constant at a given temperature, but changing the temperature alters the solubility equilibrium and its associated K_sp. As seen in Figure 1 of the passage, the solubilities of CuCl₂ and CuSO₄ salts both decrease as the temperature decreases, but the solubility of CuSO₄ decreases to a much greater extent. Consequently, when attempting to separate a mixture of CuCl₂ and CuSO₄ salts at 90 °C, cooling the mixture to 5 °C promotes the precipitation of the CuSO₄ while the CuCl₂ tends to remain in solution (Number III). To further decrease the solubility of the CuSO₄ that would still persist in solution, the common ion effect could be applied by adding Na₂SO₄ to the solution (Number II). CuSO₄ and Na₂SO₄ have the SO₄²⁻ ion in common; therefore, adding Na₂SO₄ will increase the SO₄²⁻ concentration, which will shift the solubility equilibrium toward CuSO₄ and cause the CuSO₄ to selectively precipitate out of the mixture. (Number I) Adding Cu(NO₃)₂ to the mixture would not be ideal for the separation, because this would increase the Cu²⁺ ion concentration, and both CuCl₂ and CuSO₄ contain a Cu²⁺ ion. Although CuSO₄ would precipitate to a greater extent (because it is less soluble), some CuCl₂ would still precipitate and result in a precipitate mixture. (Number IV) Lowering the pH of the mixture by adding acid would be unhelpful in the separation because Cl⁻ is not basic enough to react with the acid and shift the solubility equilibrium of CuCl₂, and any SO₄²⁻ reacting with H⁺ to form HSO₄⁻ would interfere with the precipitation of CuSO₄ by shifting the equilibrium to the right and causing more CuSO₄ to dissolve. Educational objective: The temperature dependence of solubility and the common ion effect from relevant ions on the solubility equilibrium can be used to assist in selectively precipitating compounds during separations of mixtures.

Passage Copper Plays a Vital Role as a Trace Mineral for for Biological