1. C. CaCl2(s)  Ca2+(aq) + Cl22-(aq)
QUESTION:
Which of the following best represents the dissolution of CaCl2(s) in water? A. CaCl2(s)  Ca2+(aq) + 2 Cl-(aq)
B. CaCl2(s)  CaCl2(aq)
C. CaCl2(s)  Ca2+(aq) + Cl22-(aq)
CaCl2 is ionic.
Cations are Ca2+ and anions are Cl-
The formula tells us the relative abundance of ions in the compound.
When ionic compound dissolves in water: each ion is individually hydrated
Which of the following best represents the dissolution of CaCl2(s) in water?
PAUSE CLICK
The correct answer is A. …
By now, you should know that calcium chloride is an ionic compound.
CLICK and that the cations in the compound are monatomic calcium ions with a charge of +2
HIGHLIGHT Ca2+ in choice A
… that the anions in the compound are monatomic chloride ions with a charge of –1
HIGHLIGHT Cl- in choice A….
And..
CLICK
that the formula CaCl2 reflects the fact that there are two chloride ions for every calcium ion.
When an ionic compound is dissolved in water, the ions will spread out and will be individually
surrounded by water molecules.
Symbolically, we represent this by writing the “aq” label next to the formulas of the ions.
HIGHLIGHT (aq) labels in choice A
We put a coefficient of two in front of chloride ion in order to balance the equation.
So what’s wrong with choice B. Actually, there’s nothing wrong with choice B --- chemists write equations like this all
the time. However, chemists would
interpret the equation given choice B as an abbreviation for the equation in choice A.
As for choice C, you should know that there is no polyatomic ion consisting of two chlorine atoms with a –2 charge.
CROSS OUT Cl22-(aq)
PAUSE
PAUSE END RECORDING

2. Video ID: © 2008, Project VALUE (Video Assessment Library for Undergraduate Education), Department of Physical Sciences Nicholls State University Author: Glenn V. Lo Narrator: Funded by Louisiana Board of Regents Contract No. LA-DL-SELECT-13-07/08