1. The simplest collection of ions with a total charge of zero would be….
QUESTION:
What is the formula of an ionic compound consisting of Mg2+ and PO43- ions? A. Mg2PO3, B. Mg3(PO4)2, C. Mg3PO2, D. MgPO4
The formula of an ionic compound reflects the simplest combination of cations and anions with a total charge of zero.
Cations: +2, +2, +2, +2, +2, …
Anions: -3, -3, -3, -3, -3, ….
SCRIPT:
What is the formula of an ionic compound consisting of magnesium and phosphate ions? A. Mg2PO3, B. Mg3(PO4)2, C. Mg3PO2, D. MgPO4
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The formula of an ionic compound reflects the simplest combination of cations and anions with a total charge of zero.
Each magnesium ion has a charge of +2…. So, let’s imagine a collection of these ions
Each phosphate ion has a charge of –3…. Let’s imagine a collection of these ions…
The simplest collection of ions with a total charge of zero would be….
Three cations
And two anions
Therefore,
CLICK we say that one “formula unit” of this compound consists of three cations, and two anions. The formula is Mg3(PO4)2.
Note that we must enclose the entire formula for phosphate (PO4) in parentheses.
We need to do this whenever we have more than one of a polyatomic ion in a formula unit.
The correct answer is B.
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One formula unit of this compound consists of THREE cations, and TWO anions.
The formula is Mg3(PO4)2

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