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Magnesium oxide is used in the making of the lining of blast furnaces. It is extracted from seawater as follows. Aqueous calcium hydroxide is added to seawater. Ca(OH)2 (aq) + MgCl2 (aq) + Mg(OH)2(s) + CaCl2 (aq) The magnesium hydroxide is then filtered off and roasted. Which of the following comparisons between calcium and magnesium explains why magnesium hydroxide forms?

Correct answer: D. The solubility product for Mg(OH)2 is lower than that for Ca(OH)2

  • A. Magnesium is less electropositive than calcium.
  • B. Magnesium is lower than calcium in the reactivity series
  • C. The enthalpy change of hydration for Mg2+ is less exothermic than for Ca2+
  • D. The solubility product for Mg(OH)2 is lower than that for Ca(OH)2
  • E. The magnitude of the lattice energy of Mg(OH)2 is less than that of Ca(OH)2

Explanation

The lesser the solubility product the more likely the precipitation will be. Magnesium hydroxide forms as a precipitate as compared to aqueous calcium hydroxide because the solubility product of Mg(OH)2 is lower than Ca(OH)2

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About Periodic Properties and Trends

Periodic properties arise from electron configuration and effective nuclear charge, producing trends in atomic and ionic radius, ionization energy, electron affinity, electronegativity, metallic character and reactivity. Comparisons run across periods and down groups, with attention to common exceptions. The topic also relates these trends to the behavior of s-block and p-block elements.

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