ACT Science OG Test 1 - Passage II

Questions 7-13 are based on the following passage.

A high concentration of dissolved nickel (Nᵢ²⁺) in wastewater is an environmental concern. Students studied the removal of Nᵢ²⁺ from wastewater, using ,an aqueous Nᵢ²⁺ solution as a model of wastewater. In water, hydroxide (OH-) reacts with Nᵢ²⁺ to form nickel hydroxide monohydrate [Ni(OH)₂·H₂0]. The bal­anced chemtcal equation for this reactiol), is Nᵢ²⁺ + 2OH⁻ + H₂O⟶Ni(OH)₂⋅H₂O Because the monohydrate is a solid, it can be filtered from the solution. Some of the solid will eventually dissolve if it is left in contact with the solution. The students did 2 experiments to study how reaction time and filtration method affected the removal of Nᵢ²⁺ from the aqueous Nᵢ²⁺ solution. Experiment 1 In each of Trials 1—3, Steps 1—4 were performed: 1. Thirty-two mL of aqueous 1.0 mole/L OH⁻ solution and 260 mL of aqueous 0.060 mole/L Nᵢ²⁺ solution were poured into the same flask. 2. The mixture was stirred at 22°C. for 10 min; 3 days, or 7 days. 3. Solid monohydrate was recovered by standard filtration (see Figure 1)

4. The concentration of Nᵢ²⁺ in the filtrate, CNF, was determined, in milligrams of Nᵢ²⁺ per kilogram of solu­tion (mg/kg). Experiment 2 In each of Trials 4—6, Steps 1—4 in Experiment 1 were performed except that in Step 3, solid monohydrate was recovered by vacuum filtration (see Figure 2).

The results of Experiments 1 and 2 are shown in Table 1.

1 Start 2 step1 3 step2 4 step3 5 step4 6 step5 7 step6 8 Done
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