Question

Which of the following pairs of aqueous solutions will form a precipitate when mixed?

Answer 1

(a) `"MgCl"_2 + "KOH"`

Explanation:

To determine which of these mixtures will form a precipitate, we can refer to a solubility rules chart (I am not able to post one here at the time, but you can look for one online, just type in "solubility guidelines").

To determine the products of the reaction (if all ions remain in solution, and no solid forms, then no reaction occurs), we simply exchange cations (or anions) of the two reactants. The (ideal) products for the four reactions are

• `"Mg(OH)"_2 + 2"KCl"`

• `2"LiF" + "H"_2"S"`

• `"HOH" + "LiI"`

• `2 "KNO"_3 + "H"_2"O" + "CO"_2` (`"H"_2"CO"_3` is not stable, and rapidly decomposes into water and carbon dioxide)

Referring to a solubility chart, you'll see that `"Mg(OH)"_2` is considered "insoluble", so it will form a precipitate and thus option (a) is correct.