Hello,
I'm having trouble finding the oxidation states of these compounds. Can someone please help and explain how they did it? I know the oxidation state rules but both these compounds seem to have more than one unknown that don't fit in the general rules and I just don't know how to approach them.
Zn(NO3)Cl- I know the oxidation states of Cl and O but what about N and Zn?
W(CO)6
Thanks a lot!!
@pch For the MCAT, you need not, should not, have to delve deeply into ligand types, complex oxidation schemes, as the MCAT tests the same concepts over and over. The level of difficulty on these will be fairly low and they will use obvious or fairly easy to spot exceptions to the general rules as they always have.
For example, in your NO3-, the AAMC typically won't expect you to identify the oxidation state of the individual atoms of the nirtrate ion, but you better c=recognize it carries a standard charge of -1, as does the chloride ion. This leaves Zinc, the transition metal, (which be definition and periodic location can have multiple transition states) is the molecule left to determine. A simpler method can be used with some basic rules:
1) The oxidation state of an uncombined element is zero. This applies regardless of the structure of the element: Xe, Cl2, S8, and large structures of carbon or silicon each have an oxidation state of zero.
2) The sum of the oxidation states of all the atoms or ions in a neutral compound is zero.
3)The sum of the oxidation states of all the atoms in an ion is equal to the charge on the ion.
4) The more electronegative element in a substance is assigned a negative oxidation state. The less electronegative element is assigned a positive oxidation state. Remember that electronegativity is greatest at the top-right of the periodic table and decreases toward the bottom-left.
5) Some elements almost always have the same oxidation states in their compounds
In the Zn(NO3)Cl-, you can infer that, however rare, the Zn here clearly has a charge of +1 because the overall/net charge of the entire complex ion is -1. -1 (NO3) + -1(Cl) + Zn = -1 Zn = +1 you should know the net charge on all your common ions (nitrate/nitrite, phosphate, sulfate/sulfite, etc....) You will notice a pattern to the MCAT ion pretty quickly.
HERE is a great resource on how to simply, yet accurately determine oxidation states. This is more than enough for the typical MCAT question. If they want to get deeper or more complex they can, but it would be in the context of a passage.
Hope this helps, good luck!