I was asked to predict the formula for ammonium phosphate. The explanation has to be based on the theory concerning ionic compounds.

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giorgiana1976's profile pic

giorgiana1976 | College Teacher | (Level 3) Valedictorian

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When the formula for an ionic compound has to be written, the theory says that the positive ion has to be listed first.

If 2 or more polyatomic ions occure, the polyatomic ion has to be put in paranthesis.

Phosphate is one of the most common polyatomic ions,   (PO4)^3-,having -3 negative charges and ammonium, NH4^+, is a member of the first group of ions (alkali metals) and it has one positive charge, +1.

The predicted formula for ammonium phosphate is:

(NH4)3 PO4

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mkcapen1 | Middle School Teacher | (Level 3) Valedictorian

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A compound is the combination of elements resulting in a chemical reaction/change. Some compounds are ionic which measn they are formed by combining ions. All ionic compounds include salt and hydroxides. An ionic compound is neutral. The formula for ammonium phosphate is (NH4)3PO4 NaI and Na3PO4. *Combining ammonium (ion) (NH4+) with the phosphate ion (PO43-) forms ammonium phosphate. *It needs to be a three to 1 ratio creating the formula (NH4)3PO4. *In this formula we see that the parentheses hold the ammonium ion with a 3 by it. *The 3 indicates that one takes the whole ion 3 times. *One should enclose polyatomic ions when they are taken more than 1 time. *The amount of ions taken is listed outside of the parenthesis. *Ions taken only once remain outside the parenthesis.
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revolution | College Teacher | (Level 1) Valedictorian

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The phosphate (PO4) ionic charges should be 3- while the ammonium (NH4) ionic charges should be +(positive charge). Combining these two would form a compound ammonium phosphate. To determine the formula, cross-multiply the ionic charges, so the chemical formula would be (NH4)3 PO4.

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