in this video we're going to focus on identifying oxidizing and reducing agents what you need to know is that oxidation involves a loss of electrons reduction involves a gain of electrons in addition if the oxidation number increases oxidation has occurred if the oxidation number decreases reduction has occurred so let's try this example that we have on the board what is the oxidation state of magnesium metal the oxidation state of any Pure Element in its natural state is zero so the oxidation state of Elemental bromine is also zero now in a compound it can be different magnesium is in group two of the periodic table and magnesium typically forms a plus two charge bromide usually has a minus one charge and you could see in this formula it takes two bromide ions to neutralize the positive2 charge on the Magnesium cation so clearly we can see that magnesium has a plus2 oxidation state and each individual bromine atom has a minus one oxidation state for magnesium the oxidation state increased from 0 to plus two because the oxidation number went up oxidation has occurred for magnesium magnesium was oxidized now bromine was reduced notice that the oxidation number for Bromine decreased from 0 to 1 so therefore it was reduced now the substance that is oxidized is also known as the reducing agent and the substance that is reduced is also known as the oxidizing agent now you might be wondering well why is that why is that the casee the reducing agent is the substance that causes the other element to be reduced so magnesium is considered to reduce an agent because it causes bromine to be reduced on the other hand bromine is the oxidizing agent because it causes the other substance magnesium to be oxidized so make sure you reverse it as long as you reverse it you're going to get the right answer so now let's try another example so consider this reaction zinc metal reacts with hydrochloric acid to produce hydrogen gas and zinc chloride now what I want you to do I want you to pause the video and try this practice problem yourself and then unpause it to see if you have the right answer so let's begin what is the oxidation state of zinc for any pure metal in its natural state if if you have a Pure Element it's zero now in htl you need to realize that hydrogen usually has a plus one charge and chlorine like all of the other halogens like chlorine bromine iodine Florine as an ion they typically have a minus one charge so the oxidation state of hydrogen is+ one and for chlorine it's minus one now here we have elemental hydrogen gas we don't have a compound we have a Pure Element so the oxidation number for Elemental hydrogen is always going to be zero it's zero for any Pure Element now here we have a compound now we know that chloride has a minus one charge so and it's two of them which means that zinc has to have a plus two charge now if you feel a little unsure why zinc has a plus two oxidation state you can write an equation zinc plus the two chlorine atoms should have an oxidation state of zero because over all zinc chloride is neutral so we're going to solve for the oxidation state of zinc so let's replace zinc with an x uh symbol and we know that chlorine as an ion has a minus one charge so let's uh replace CL for negative 1 so right now we have x - 2 is equal to Z so if we add two to both sides we're going to get the oxidation state of zinc which is uh plus two and so that's one way you can calculate it if you're ever unsure so now let's finish this problem so we see that the oxidation number for Zinc increased from Z to plus two so zinc was oxidized it lost two electrons now the oxidation state for hydrogen decreased from 1 to zero so there therefore it was reduced the hydrogen atoms or the hydrogen ions they gained electrons which is associated with reduction now the substance that is oxidized is also known as the reducing agent and the substance that is reduced is the oxidizing agent so zinc is considered a reducing agent because it caused the other substance Hydro hydrochloric acid to be reduced and the hydrochloric acid is the oxidizing agent Bec because it caused the other substance zinc to be oxidized so I hope that makes sense but let's go ahead and try another example for the sake of practice so let's say if we have sodium bromide plus chlorine gas and it's going to produce a solution of sodium chloride plus liquid bromine now go ahead and identify the oxidizing and the reducing agent sodium typically has a plus one charge as an alkaline metal it's always going to have a plus one charge bromide is a halogen and most halogens usually form minus1 charges now chlorine is a Pure Element so it's going to be zero and bromine br2 is a Pure Element so now which substance is oxidized and which substance is reduced notice that sodium is the spectator ion the charge on sodium doesn't change so we don't have to worry about that now notice that for Bromine the oxidation state increased and went up from1 to zero so therefore we could say uh the bromide ion within sodium bromide was uh oxidized and if you look at cl2 the oxidation number decreased from zero to minus one and so we could say that chlorine was reduced so therefore chlorine is the oxidizing agent and sodium bromide is the reducing agent if you notice most metals like zinc and magnesium in the last two examples that we've considered most uh Elemental metals they tend to form reducing agents like zinc and magnesium are good reducing agents most nonmetals in their Elemental form like cl2 like chlorine bromine most non-metals usually form good oxidizing agents like oxygen O2 oxygen is a nonmetal and it's a good oxidizing agent in fact the word oxidizing agent comes from oxygen so what about uh this example h2+ O2 turns into H2 so feel free to pause the video and try this example so hydrogen gas on the left it's in its Elemental form so it has an oxidation state of zero oxygen also has an oxidation state of zero now in water in a compound it's going to be different oxygen usually forms aus2 charge and for hydrogen when it's bonded to a non-metal it usually has a plus one charge now hydrogen when bonded directly to a metal typically has a negative-1 oxidation state but when bonded to a non metal it's plus one so now if we focus on the hydrogen atoms we can see that hydrogen went up from Z to one so therefore hydrogen was oxidized now oxygen decreased from 0 to -2 so because it gained two electrons it was reduced reduction occurred hydrogen lost an electron as it went from 0 to one now the substance that is oxidized is the reducing agent and the substance that is reduced is the oxidizing agent so we can see that O2 is the oxidizing agent and H2 is the reducing agent so now let's work on our final example chlorite plus per chlorate yields chlorate so go ahead and identify the oxidizing and the reducing agent now we need to find the oxidation state of every element in this compound or in this uh equation whenever oxygen is bonded to another element typically it has a negative -2 charge so for every oxygen that's in this equation it's going to have an oxidation state of -2 the exception is if oxygen is bonded to Florine in that case it's going to have a positive oxidation state or if it's in the form of peroxide or superoxide in the form of oxide it has a min-2 oxidation state in peroxide it has a negative 1 oxidation state in super oxide it has a negative one2 oxidation state but we don't have to worry about that for this example so let's start with chloride let's calculate the oxidation state of chlorine in chloride so we have CL plus two oxygen atoms and it has a net charge of1 so let's replace CL with X and let's plug in -2 for oxygen so 2 * -2 is-4 and if we add four to both sides we can see that X is equal to pos3 so that's the oxidation state of chlorine in chloride so now let's do the same thing but for chlorine in per chlorine so we have one chlorine atom plus four oxygen atoms and the net charge is minus one so 4 * -2 is8 and if we add 8 to both sides -1 + 8 is 7 so that's the oxidation state of chlorine in cl4 so now let's do the same thing for chlorine you can probably see that it's going to be + 5 but we'll work out the example so we have CL plus three oxygen atoms equals a net charge of1 so 3 * -2 is -6 and uh if we add six to both sides we can see that -1 + 6 is + 5 so that's the oxidation state of chlorine in chlorine so now there's two chlorate ions on the right side so one of the chloride ions turns into chlorate and the other per chlorate ion turns also into chlorine so here chlorine went from three to five so it lost two electrons and the oxidation number went up so so therefore the chlorine atom in cl2 was oxidized and the chlorine atom in per chlorine it went from seven to five so it gained two electrons it was reduced so reduction occurred therefore the chloride ion is the reducing agent and the per chlorate ion is the oxidizing agent and so that's it so now you know how to identify the oxidizing and the reducing agent so I hope this all makes sense to you and thanks for watching