In the compound K[Co(C₂O₄)₂(H₂O)₂] (where C₂O₄^2- = oxalate) the oxidation number and coordination number of cobalt are, respectively A) -1 and 4. B) -1 and 6. C) 3 and 4. D) 3 and 6. E) 1 and 6.

Question

Quizplus · Accepted Answer

The coordination number of cobalt in this compound is 6 because there are six ligands (oxalate and sulfur) surrounding the central metal ion. 
To find the oxidation number of cobalt, we can use the overall charge of the compound and the known charges of the ligands. 
K has a charge of +1 and there is one of them, so its contribution to the overall charge is +1. 
The oxalate ligand has a charge of -2 and there are two of them, so their contribution to the overall charge is -4. 
The sulfur ligand has a charge of -2 and there are four of them, so their contribution to the overall charge is -8. 
Finally, the HS ligand has a charge of -1, and there is one of them, so its contribution to the overall charge is -1. 
Adding up these charges, we get a total charge of -12. Therefore, the sum of the oxidation states of all atoms must be +12 to balance it out. 
Let x be the oxidation state of cobalt. Then, 
+1 + (-4) + (-8) + (-1) + x = +12 
Simplifying the left side, 
-12 + x = +12 
Solving for x, 
x = +3 
So the oxidation number of cobalt is +3, and the correct answer is (D).

In the Compound K[Co(C2O4)2(H2O)2] (Where C2O42- = Oxalate) the Oxidation

In the Compound K[Co(C₂O₄)₂(H₂O)₂] (Where C₂O₄^2- = Oxalate) the Oxidation