General Chemistry 2

Question

What occurs when aqueous lithium hydroxide, 

LiOH, reacts with aqueous magnesium chloride, 

MgCl2?

Answers:

MgCl2 forms as a precipitate.

Mg(OH)2 forms as a precipitate.

LiOHforms as a precipitate.

No precipitate forms and no reaction occurs.

LiCl forms as a precipitate.

Answer 1

We are going to do double replacement and check if any of the new compounds that we have made are insoluble, by using a solubility chart. You may need to google one and follow along but it has metals down the column and the anions across the rows, and in the boxes where they intersect it tells you if they are soluble (S) or insoluble (I).

The reaction:

(I assuming you understand balancing the reaction and using the charges to create the correct compound)

2LiOH + MgCl2 —> 2LiCl + Mg(OH)2

We need to check if LiCl or Mg(OH)2 are insoluble.

From the solubility chart:

Things that are insoluble with Cl: Ag, Pb, Hg

Things that are insoluble with OH: everything except group 1 metals, Al, and NH4

As we can see, Mg is insoluble with OH because it’s not in group 1. Therefore there would be a precipitate of Mg(OH)2 that falls out of the solution.