Question

Determine the concentrations of BaBr2, Ba2 , and Br– in a solution prepared by dissolving 1.38 × 10–4 g BaBr2 in 2.00 L of water. Express all three concentrations in molarity. Additionally, express the concentrations of the ionic species in parts per million (ppm).

Answer 1

The correct answer to this question is this one:

Assuming all the barium bromide dissolved (which it should), the concentration of BaBr2 in solution should be zero: it should all dissociate into Ba+2 and 2Br- ions.

Turn those grams of BaBr2 into moles of BaBr2, then divide by the volume to get the concentration.

Recognize that every formula unit of BaBr2 has one ion of Ba+2, and 2 ions of Br-1. That means that when this substance dissociates, you'll get one concentration of Ba+2 ions, and a concentration of Br- ions TWICE as large. Whatever the concentration of Ba+2 ions is that you calculate, double it for the conentration of the Br-1 ion.