Question

A student writes the name of Co₂S₃ as "Cobalt(II) Sulfide". Why is this incorrect? Check all that apply.

a) The student gave the wrong cation name
b) The student gave the wrong anion name
c) The student wrote the wrong roman numeral
d) The Roman numeral is supposed to represent charge, not subscript
e) The student wrote a roman numeral when there shouldn't be any.
f) The student forgot to write the roman numeral.

Answer 1

The student's naming of Co₂Sₑ as 'Cobalt(II) Sulfide' is incorrect because the cobalt cation has a charge of +3 in this compound, not +2, which should be properly denoted with a roman numeral III, making the correct name 'Cobalt(III) Sulfide'.

Step-by-step explanation:

The naming of Co₂Sₑ as "Cobalt(II) Sulfide" is incorrect for several reasons. First, the anion sulfide is correct, however, the roman numeral provided does not correctly represent the charge of the cobalt cation.

Cobalt can have multiple oxidation states, so it is essential to identify the correct charge when naming the compound. Since sulfur (S) has a 2- charge each and there are three of them, the combined charge of the sulfides is 6-. Consequently, the cobalt cations must have a combined charge of 6+ to balance this.

Since there are two cobalt atoms, each must be Cobalt(III) to balance the overall charge, giving us the correct name of Cobalt(III) Sulfide.