1. Which of the following is insoluble in water?
QUESTION:
Which of the following is insoluble in water?
A. CuCl2, B. Hg2Cl2, C. HgBr2, D. Ca(NO3)2
Solubility rules (for common ionic compounds):
Compounds of the following are always soluble: sodium, potassium, ammonium, nitrate, nitrite, perchlorate, acetate
Compounds of the following are generally soluble:
chloride, bromide, iodide --- except with silver, lead(II), mercury(I), and copper(I)
Sulfate -- except with lead(II), barium, strontium, calcium, and mercury(I)
Fluoride --- except with lead(II) and group II(A)
The rest are generally insoluble. Exceptions:
sulfides of group II(A) are soluble
hydroxides of calcium, strontium and barium are moderately soluble.
Which of the following is insoluble in water?
Copper(II) chloride…
Mercury(I) chloride…
Mercury(II) bromide… Or
Calcium nitrate
PAUSE
CLICK
To answer this question, use the solubility rules for common ionic compounds….
You’re likely to see different versions of these rules in different textbooks. They are all pretty much equivalent although
some textbooks include more ions than others.
In general, the rules will tell you
CLICK which compounds are always soluble…
CLICK which compounds are generally soluble and what the exceptions are….
And that pretty much anything else is insoluble and what the exceptions are.
Let’s apply the rules to each of the choices.
Let’s start with choice A…. Copper(II) chloride
CALLOUT “copper(II) chloride” pointing to CuCl2
Rule 1 does not apply. It doesn’t say anything about copper or chloride ions.
So, we move on to the second rule.
The second rule tells us that chlorides are generally soluble.
HIGHLIGHT “chloride”
… unless it is in combination with silver, lead(II), mercury(I), or copper(I)
HIGHLIGHT “except with” and “copper(I)”
The compound we’re given is copper(II) chloride, not copper(I) chloride. Therefore, the compound is soluble.
Choice A is also incorrect.
CROSS OUT Choice A
How about choice B…. Mercury(I) chloride….
CALLOUT “Mercury(I) chloride” pointing to Hg2Cl2
Again rule 1 does not apply.
Rule 2 applies in this case. Rule 2 tells us that chlorides are generally soluble.
However, mercury(I) chloride is an exception.
HIGHLIGHT “except with” and “mercury(I)”
Therefore, mercury(I) chloride is insoluble.
The question is asking us to identify the insoluble compound.
Therefore, choice B is correct.
Let’s verify that choices C and D are, in fact, soluble in water.
Let’s examine choice C…. Mercury(II) bromide
CALLOUT “mercury(II) bromide” pointing to HgBr2
Again, the first rule does not apply. It doesn’t say anything about mercury(II) or bromide.
So, we go on to the next rule. It says that bromides are generally soluble.
HIGHLIGHT “bromide’
…. Unless it is in combination with silver, lead(II), copper(I), or mercury(I)
…Our compound is mercury(II) bromide, not mercury(I) bromide
… therefore, it is NOT an exception to the rule. Mercury(II) bromide is soluble in water.
Finally, let’s look at choice D…. Calcium nitrate
CALLOUT “calcium nitrate” pointing to Ca(NO3)2
Rule 1 applies in this case. All nitrates are soluble.
HIGHLIGHT “nitrate” in rule 1
Therefore, calcium nitrate is soluble.
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