Chapter 2 - Atoms, Molecules, and Ions - Questions and Exercises - Exercises - Page 87: 2.95

(a) cobalt (III) chloride (b) iron (II) sulfate (c) copper (II) oxide

(a) cobalt (III) chloride Cobalt (Co) is a transition metal that has more than one valence. Let us look at the anion to see if we can determine which valence we have for iron. Chlorine (Cl) has a valence of 1-. We need three atoms of chlorine for every atom of cobalt; therefore, we know that cobalt has a valence of 3+. To specify that the valence of this particular atom of cobalt is 3+, we place the Roman number III in parentheses next to the name of the cation, cobalt. We then add the name of the anion (chlorine), changing its ending to $-ide$. (b) iron (II) sulfate Iron (Fe) is a transition metal that has more than one valence. Let us look at the anion to see if we can determine which valence we have for iron. We look to Table 2.2 on page 65 of our book to see that sulfate (SO$_4$$^{2-}$) has a valence of 2-. Iron and sulfate are present in a 1:1 ratio in this compound; therefore, we know that iron has a valence of 2+. To specify that the valence of this particular atom of iron is 2+, we place the Roman number II in parentheses next to the name of the cation, iron. We then add the name of the anion (sulfate) as-is. (c) copper (II) oxide Copper (Cu) is a transition metal that has more than one valence. Let us look at the anion to see if we can determine which valence we have for iron. Oxygen (O) has a valence of 2-. Copper and oxygen are present in a 1:1 ratio in this compound; therefore, we know that this atom of copper has a valence of 2+. To specify that the valence of this particular atom of copper is 2+, we place the Roman number II in parentheses next to the name of the cation, copper. We then add the name of the anion (oxygen), changing its ending to $-ide$.