Question

What is the name of the compound CrPO4 • 4H2O?

Answer 1

Hydrated chromium(III) phosphate or chromium(III) phosphate tetrahydrate.

Explanation:

We first look at the first part of the chemical formula, which is simply `CrPO_4`. Notice that this molecule has a phosphate `(PO_4^(3-))` ion bonded to a chromium ion, which we will find out its charge.

Let `x` be the charge of the chromium ion. So, we get:

`x+(-3)=0`

`x-3=0`

`x=3`

So, chromium is in its `+3` oxidation state, and will get the name chromium(III).

Combining the names of the ions, we get the first part of the name: chromium(III) phosphate.

Now, we look at the second part of the name, which is the `*4H_2O` part. It just simply means that there are four water ligands attached to the compound. The new compound is now therefore called hydrated.

We can now use the final name of the compound, which will be hydrated chromium(III) phosphate. If you want to be more specific, you can say that the compound is called Chromium(III) phosphate tetrahydrate, where "tetra-" stands for `4`, as there are four water molecules attached to the compound.