What is the oxidation state of the metal in each of the complexes?

a. [Ni(CN)₅]^3–

b. Ni(CO)₄

c. [Co(en)₂(H₂O)Br]²⁺

d. [Cu(H₂O)₂(C₂O₄)₂]^2–

e. Co(NH₃)₃(NO₂)₃

Video transcript

Welcome back everybody. Our next problem says, identify the oxidation number of each metal center in the following co-ordination compounds. We have five different co-ordination compounds listed as number one through five. And our answer choices A through D are just listings of the oxidation number of each of these. And we need to identify which of them, list them all correctly. So rather than read them all out loud, we'll just work our way through the different compounds and then identify which answer choice is correct. So let's turn our attention to co compound number one, we have an ion with an overall charge of positive two. So it's in brackets and then it's cr and in parentheses, lowercase e lowercase N subscript two and then in parenthesis co and then cl. So we have a central ion of chromium and our ligands are ethylene diamine. That's the en two of those, then one carbonyl, that's our co and then a chloride ion. So to figure out the oxidation number of chromium, we know that all the charges of each of the ligands and the central atom have to add up to the overall charge of our coordinations compound So our overall charge is positive too. So that must equal the oxidation number I'm gonna put on of chromium plus. So ethylene diamine is neutral. So that will be zero for those. Then we've got carbonyl that's also neutral. So another zero and then the chloride ion has a charge of negative one. So let's solve for the oxidation number of chromium which would equal plus two and then move everything else to that other side, you'll have positive two plus one. So that will give us positive three. So oxidation number of chromium is plus three. So let's look through our answer. Choices. Choice A has oxidation number of chromium as plus three. So that could be correct. Choice B has oxidation number of chromium in number one as plus two. So we can rule out choice B choice C has in number one, oxidation number of chromium plus two. So rule out choice C and then choice D has number one, oxidation number of chromium plus three. So that is also correct. So we're down to choice A and D here. So we've already eliminated two answer choices. Let's move on to compound number two where we have no overall charge. And our molecule is co then in parentheses, H2O subscript three and in parentheses, CN subscript three. So we've got our central Cobalt molecule with three waters and three cyanide as our ligands. So our overall charge is zero, which will equal the ox station number of Cobalt. In this case, plus our waters are neutral. So plus zero for the waters and cyanide and then our cyanide ligands have a charge of negative one and there's three of them. So have plus three multiplied by negative one. So solve for our oxidation number of cobalt will equal zero plus three. So we have a positive three as our ox station number. So lets check that against our answer choices. And we have left choice A and choice D. If we look at choice A, it says the oxidation number of cobalt and number two is zero incorrect. So now we've ruled out A so we're actually down to our answer choice D it correctly shows number two oxidation number of Cobalt S plus three. So if I were on a test, I would be picking choice D and moving on, not even having to look at the rest of my molecules. But because this is a video, we're going to be thorough and work through them all. So on to number three, number three has an overall charge of two minus. So everything else is within brackets and we have N I in parentheses, C 204, subscript two in parentheses, NH three, subscript two. So we've got a nickel central atom and ligands of two and the C 204 is oxalate and our NH three is the amine group and we've got two of those. So our overall charge as we said is negative two that will equal the oxidation number of nickel plus. So our first group of ligands are two oxalate, oxalate groups, oxalate has a charge of negative two. So we'll have two multiplied by negative two and then the amino groups are neutral. So we've got a plus zero as their input. So oxidation number of nickel equal to negative two plus four and we get plus two for nickel there. Highlight that and look at our answer choices. Confirm that choice D is correct here and indeed says oxidation number of nickel is plus two. So on to molecule number four, this is all in brackets with a charge of three minus and it's fe and then in parenthesis oh subscript five. So central atom iron, it's got a charge of negative three on the overall ion and our ligands are five hydroxide groups. So our overall charge again is negative three equals the oxidation number of iron. And our contribution of the ligands five hydroxide groups and hydroxide has a charge of negative one. So plus five multiplied by negative one. So our oxidation number of iron will equal plus two. Highlight that and double check it against our answer choice number four, oxidation number of iron plus two. So now we're on our final compound which is number five and there's no charge overall we've got cr and then in parenthesis, co subscript six. So chromium is the central atom with six carbon groups. So overall charge zero equals the oxidation number of chromium plus the carbon groups are neutral. So plus zero, and we have zero equals the oxidation number of chromium. And indeed, when we look at our answer choice, number six, choice five is there oxidation number of chromium zero? So we have our answer choice confirmed by checking it against all those atoms. The co ordination number of each metal center is correctly identified in choice D and number one chromium plus three, number two cobalt plus three, number three nickel plus two, number four iron plus two and number five chromium zero. See you in the next video.