Solution: What is the name of the following ion: H 2PO4-?

Problem

What is the name of the following ion: H 2PO4-?

Solution

For this problem, we are asked to name the ion H2PO-.

First, we need to determine whether it is an ionic compound, covalent compound or an acid (binary or oxyacid). Based on its chemical formula, H2PO4- is similar to an oxyacid  

**H+ ion bonded to PO4 which is a polyatomic anion containing O. 

An oxyacid is a covalent compound that contains an H+ ion connected to a polyatomic ion containing oxygen.

Recall that the rules for naming ions are similar to naming oxyacids in gas phase (not aqueous):

1. Start with Hydrogen, write a prefix to indicate the number of H, (except for mono) 


The numerical prefixes are:

Mono – 1     Di – 2

Tri – 3          Tetra – 4

Penta – 5     Hexa – 6

Hepta – 7     Octa – 8

Nona – 9      Deca – 10


2. For Polyatomic ions they retain their name 

**no prefixes needed 

**no need to change ending to -ide 

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