1. FeSO4 is an ionic compound. Cation is iron(?). Need to figure out “?”
QUESTION:
Which of the following is correct name for FeSO4? A. iron(I) sulfate, B. iron(II) sulfate C. iron(III) sulfite, D. iron sulfite
FeSO4 is an ionic compound.
Cation is iron(?). Need to figure out “?”
Anion is sulfate: SO42-
A compound is electrically neutral. Overall charge=0. Total negative charge: -2 Total positive charge: +2
Therefore, the cation is Fe2+
Name of cation is iron(II), or ferrous
SCRIPT:
Which of the following is correct name for FeSO4? A. iron (I) sulfate, B. iron (II) sulfate C. iron(III) sulfate, D. iron sulfite
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
FeSO4 is an ionic compound…. We know this because iron is a metallic element. When atoms of metallic elements form compounds,
they typically end up as positively charged ions
For an ionic compound, the name is simply the name of the cation, followed by the name of the anion.
So let’s identify the cation and the anion based on the given formula.
We know our is an iron ion. However, iron is a transition metal. Since transition metals are generally known to form more than one kind of ion, we need to specify which kind we have. We do this by specifying the charge in roman numeral, in parentheses.
HIGHLIGHT “?” in iron(?)
At this point, we can rule out choice D --- it does not specify the charge of iron.
CROSS OUT choice D
From the formula, we should be able to recognize that the anion is sulfate. The only known polyatomic ion consisting of a sulfur atom and four oxygen atoms has a charge of –2, and it’s called sulfate. This is one of those trivial things that you just need to know.
At this point, then we can rule out choices C and D. The name for the anion is incorrectly given in these choices as sulfite, not sulfate.
CROSS OUT sulfite in choices C and D
CLICK To figure out the charge of the iron ion in this compound, we use the fact that a compound is electrically neutral. Therefore, the overall charge must be zero.
CLICK We know that a sulfate ion has a –2 charge.
CLICK Therefore, the positive charge carried by the iron ion must be +2.
CLICK The cation is Fe with a +2 charge,
CLICK and it’s called iron two
HIGHLIGHT iron(II) or, in the old days,… ferrous.
The name of the compound is simply the name of the cation…. Iron two
HIGHLIGHT mercury(II) in choice B
Followed by the name of the anion… sulfate
HIGHLIGHT sulfate in choice B
Iron two sulfate…. is also called ferrous sulfate
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