Problem: The concentration of Mg2+ in seawater is 0.052 M. At what pH will 99% of the Mg 2+ be precipitated as the hydroxide salt? [Ksp for Mg(OH)2 = 8.9 X 10 -12.]

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FREE Expert Solution

99% of Mg2+ is precipitated → 1% is left in the solution

[Mg2+] = 99% (0.052 M) 

[Mg2+] = 5.2×10‒4 M

when 99% of Mg2+ is precipitated, 5.2×10‒4 M of Mg2+ is left in the solution


Ksp Mg(OH)2 = 8.9×10‒12 M

Ksp=[Mg2+][OH-]28.9×10-12(5.2×10-4)=(5.2×10-4)[OH-]2(5.2×10-4)1.7115×10-8=[OH-]2

[OH] = 1.3082×10‒4 M


pOH = ‒log [OH]

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Problem Details

The concentration of Mg2+ in seawater is 0.052 M. At what pH will 99% of the Mg 2+ be precipitated as the hydroxide salt? [Ksp for Mg(OH)2 = 8.9 X 10 -12.]

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Our tutors have indicated that to solve this problem you will need to apply the Selective Precipitation concept. If you need more Selective Precipitation practice, you can also practice Selective Precipitation practice problems.

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Based on our data, we think this problem is relevant for Professor Parr's class at YU.

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Our data indicates that this problem or a close variation was asked in Chemistry: An Atoms First Approach - Zumdahl 2nd Edition. You can also practice Chemistry: An Atoms First Approach - Zumdahl 2nd Edition practice problems.