9C.3 Textbook Help

[Natalie Swerdlow 3K]

In question 9C.3, how do you determine how many Br are in the formula when naming tetraamminediaquacobalt(III) bromide. For example, the answer is [Co(NH3)4(SO4)]Br3. Why are there 3 Br in this formula?

[jennaj3k]

Br is the anion in this compound, and its important to look at the overall charge of the compound. The 4 ammines and the 2 aquas are neutral, but cobalt has a charge of +3. Since we see that the overall compound is neutral, the anion needs to have a total charge of 3-. Since Br is a halogen and its oxidation state is -1, 3 Br ions gives us charge 3-. This makes the overall compound neutral.

[Luke Schwuchow 14A]

You figure this out by looking at the charge of the molecule. The main compound has a charge of +3, meaning that in order to have a nuetral compound you will need 3 Bromines. This is because each bromine has a charge of -1. So -1(3) + 3 = 0