Passage II

A high concentration of dissolved nickel () in wastewater is an environmental concern. Students studied the removal of from wastewater, using an aqueous solution as a model of wastewater.

In water, hydroxide () reacts with to form nickel hydroxide monohydrate . The balanced chemical equation for this reaction is


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 from the aqueous solution.


Experiment 1

In each of Trials 1-3, Steps 1-4 were performed:

1. Thirty-two mL of aqueous 1.0 mole/L solution and 260 mL of aqueous 0.060 mole/L solution were poured into the same flask.

2. The mixture was stirred at 22℃ for 10 min, 3days, or 7 days.

standard filtration (see Figure 1).


4. The concentration of in the filtrate, CNF, was determined, in milligrams of 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.


Table 1 adapted from K. Blake Corcoran, Brian E. Rood, and Bridget G. Trogden, "Chemical Remediation of Nickel(Ⅱ) Waste: A Laboratory Experiment for General Chemistry Students." ©2010 by Division of Chemical Education, Inc., American Chemical Society.

8. Based on the results of Experiments 1 and 2, what combination of reaction time and filtration method resulted in the lowest concentration of dissolved nickel in the filtrate?

Answer and Explanation

Your Answer is

Correct Answer is F

Explanation

From figure 1, it can be seen that trials 1-3 were carried out in a standard environment;

From figure 2, it can be seen that trials 4-6 were carried out in a vacuum;

Thus, from the data in table 1, it can be seen that the CNF value is smaller in the standard environment. Comparing trials 1-3, it can be seen that the shorter the reaction time, the smaller the CNF value