Assume that the seawater sample described in Example 18-6 contains approximately 440 g Ca²⁺ per metric ton (1 metricton = 10³ kg; density of seawater = 1.03 g/mL)

(a) Should Ca(OH)₂(s) precipitate from seawater under the stated conditions, that is, with [OH^-] = 2.0 x 10‾³ M?

(b) Is the separation of Ca²⁺ from Mg²⁺ in seawater feasible?

Example 18-6

The first step in a commercial process in which magnesium is obtained from seawater involves precipitating Mg²⁺ as Mg(OH)₂(s). The magnesium ion concentration in seawater is about 0.059 M. If a seawater sample is treated so that its [OH‾] is maintained at 2.0 x 10‾³ M, 

(a) what will be [Mg²⁺] remaining in solution when precipitation stops (K_sp = 1.8 x 10‾¹¹)?

(b) Is the precipitation of Mg(OH)₂(s) complete under these conditions?