1. Ammonium sulfide is an ionic compound. Cation is ammonium ion. NH4+
QUESTION:
Which of the following is correct formula for ammonium sulfide? A. (NH4)2S, B. NH4SO3, C. (NH3)2SO4
Ammonium sulfide is an ionic compound.
Cation is ammonium ion. NH4+
Anion is sulfide: S2-
A compound is electrically neutral. The formula for an ionic compound should reflect the simplest set of ions with a total charge of zero. NH4+, NH4+, S2- total charge=0
SCRIPT:
Which of the following is correct formula for ammonium sulfide? A. (NH4)2S, B. NH4SO3, C. (NH3)2SO4
PAUSE
To determine the formula of a compound given its name, we need to first classify the compound, then apply the rule for that type of compound.
CLICK
Ammonium sulfide is an ionic compound….
This is trivial information. You should know that if the name of a compound starts with ammonium, it’s ionic and the cation is ammonium.
CLICK and that the formula of ammonium ion is NH4 with +1 charge.
At this point, we can eliminate choice C. There is no NH4 grouping in the formula given in choice C.
CROSS OUT 3 in (NH3)2SO4
CLICK The first part of the name of any ionic compound is the name of the cation.
The rest of the name of the name of the anion.
In this case, it’s sulfide.
By now, you should know that if you change the name of a nonmetallic element to ide, you are dealing with a monatomic
anion derived from that element. So, sulfide comes from a sulfur atom that has gained electrons. Based on its location in the periodic table, you should be able to deduce that sulfide has a charge of –2. Sulfur belongs to group 6A; atoms in this group tend to form monatomic anions by gaining two electrons. So the formula for sulfide is S, with a –2 charge.
HIGHLIGHT S2-
At this point, we can eliminate choice B. There should be no oxygen in the formula.
CROSS OUT O in NH4SO3
There is no oxygen in ammonium. There is no oxygen in sulfide.
So the correct answer must be choice A. Let’s verify this. CLICK A compound is electrically neutral. The formula for an ionic compound should reflect the simplest set of ions with a total charge of zero.
The subscript for ammonium is 2 and the subscript for sulfide is not written --- that means it’s implied to be one.
Each ammonium ion has a charge of +1 and each sulfide ion has a charge of –2.
HIGHLIGHT as numbers are called
+1… plus +1… plus –2… equals zero
Therefore, the total charge implied in the formula is 0. The formula given in choice A is correct.
CLICK 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