Assign oxidation numbers to each atom in Borax, Na2B4O7, a mineral used in laundry detergent. (LO 4.18)

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Hello everyone. So in this video we're trying to determine the oxidation state of each element and calcium oxalate, which is this molecular formula here. This is a crystal that's found in kidney stones. So oxygen usually has an oxidation state of negative two. With some exceptions. Those exceptions is if it's reacting with a peroxide or super oxide, which we don't have in this case, then we can go ahead and assume that oxygen will provide a oxidation state of negative two. So we see over here right off the bat that this overall charge of the molecule here is equal to zero is a neutral molecule is very important when doing calculations. So I'm gonna go ahead and write that out. So the overall charge is equal to zero. Ready go ahead and let X equal to the oxidation state of carbon because that's our unknown for our calcium here. That's in group to a and therefore the predictable oxidation state of calcium is going to be positive too. So again, I'm just going to rewrite this molecule here of calcium, oxalate, that's CAC- 204. So we said earlier that are calcium here has a plus two oxidation state. Our carbon here is unknown to the X. And then each oxygen provides a negative two oxidation state. So some of all of our oxidation states should equal to zero because we have an overall neutral molecule and then from our calcium we have a plus two we have two atoms of our carbon. So we have a two coefficient and then each calcium, our carbon is X. So that we have a two X. Again we're just summing up everything. That's why I have all these plus signs in between. And then we have four atoms of oxygen. And each option provides a oxidation state of -2. Alright, so simple arithmetic. Here we're just simplifying. So four times negative two is negative eight. I'm gonna go ahead and combine my positive to a negative eight. And that gives us two x. Plus our negative six. I'll bring the negative six to the other side. So I'll simply add it to both sides and we get a positive six equaling 22 X. So now I'm solving for X. I'm dividing both sides by two. That gives me a positive three equaling two X. So therefore then The oxidation state oxygen is equal to -2. Are calcium is equal to positive two and then are unknown carbon is equal to positive three. So out of these five choices that are given the one that matches what we just sell for will be a. So A is going to be my final answer for this problem

Assign oxidation numbers to each atom in Borax, Na2B4O7, a mineral used in laundry detergent. (LO 4.18)

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Key Concepts

Oxidation Numbers

Polyatomic Ions

Balancing Charges