Ch 5 Redox Rxn Review

追加: 2026-05-12

[00:00:00]hello began a review chapter 5 from chem 1a which is about oxidation reduction reactions just one section in that chapter we call those reactions redox reactions that's just the short for oxidation reduction reactions and oxidation reduction reactions or redox reactions refers to reactions that involve transfer of electron or electrons so in the reaction you have one species that donates the electron and is called the reducing agent the animal grabs the electron it's called the oxidizing agent and so they exchange electrons and that's what the reaction is about and some terminologies here oxidation that refers to loss of electrons takes some thing loses electrons it's getting oxidized you can think of it as you losing money whenever you lose money you're getting oxidized and reduction refers to gain of electrons so that every you know you give your page take and you get paid you gain money so you're getting reduced so that's good oxidation results an increase oxidation number oxidation number is just the way of keeping track of electrons we'll go over that or how to assign it a little later or review and rather and reduction refers so oxidation loss of electron which is all same increase in oxidation number so the more electrons you lose the higher oxidation matters if iron goes from plus 2 to plus 3 its oxidation number is increasing since losing more electrons when it's plus students lost two electrons when it goes to plus 3 is lost 3 electrons down so that oxide reduction refers to gain of electrons which results in decrease of oxidation number so for example of chlorine goes from CL 2 which is neutral 2 CL minus chloride it gained 1 electron to God reduced and if oxidation number decrease let's look at an example copper 2 reacting with zinc metal producing copper metal and zinc ion probably due to chem 22 you test about this so in here we want to know what got oxidized what got reduced so copper - I've been from +2 to 0 so it's oxidation number decrease so we gained electrons and so therefore it was reduced to copper 2 was reduced here zinc went from zinc metal went from 0 to plus 2 so it lost two electrons that are for zinc metal was oxidized so in this reaction copper 2 ion was reduced and zinc metal was oxidized so we just talked about oxidizing and reducing agents so let's do it a little more formally here so over here if you look on Sinai's the agent then I call those electron grabbers electron donors so for those of you who have kids you know oxidizing agents you can think about as kids there's no money grabbers electron grabbers and reducing agent would be your employer day you don't give you monies that are reducing agent and those are money donors electron donors so anyways oxidizing agents they will oxidize and other species during the reaction so they themselves will get reduced and that's the part that sometimes students get mixed up in so oxidizing agents they actually get reduced during the reaction they're the ones that want to grab electrons or electrons seekers grabbers reducing agents on the other hand they get oxidized even to reaction because they perform the act of reduction of something else they give electrons to something else and they themselves will get oxidized during the reaction so going back to that reaction copper toy was reduced therefore copper to ion is the oxidizing agent the electron Grabber in that reaction zinc metal was oxidized therefore it was the reducing agent the electron donor in that reaction now what if we had a more complicated case like here hydrogen and permanganate by the way this is not balance reactive nitrogen monoxide gas producing manganese 2 ion nitrate ion and water and we wanted to assign and figure out what's the oxidizing agent what's the reducing agent who's losing electrons meaning reducing agent who's grabbing electrons meaning oxidizing angels well the more complicated case letters like that you would have to assign oxidation numbers so that they can keep track of electrons so going over here the rules for assigning oxidation numbers I'm going to show you those few seconds they're based on this premise for example let's say you have the water molecule and in water you have oxygen and hydrogen oxygen is more electronegative remember electronegativity refers to tendency of an element to want to cool electron toward itself been involved in a chemical bond and so fluorine was the most electronegative element of the table and as you move the Rays from floating they like to make it CVT decrease so oxygen is right next to fluorine so it's the second most electronegative on the table so it's more electronegative than hydrogen so when we are assigning electrons we assign them to the more electronegative element in this case oxygen and then you compare how many oxygen have how many electrons oxygen has assigned to it compared to the number of valence electrons that it normally has so oxygen normally has six valence electrons it's in group six days to six valence electrons and here I have eight electrons assigned to it one two three four five six seven eight so as a result oxygen is assigned and oxidation of minus two because they're assigning two extra hydrogen is in Group one it has one valence electron and in this case it has no electrons assigned to it so it's oxidation number is plus one and so the rules for assigning oxidation numbers are like that so generally oxygen you know it wants to make two bonds international tendencies to make two bonds cuz it has two unpaired electrons and so wait does that since it's the second most electronegative element on the table it will get those electrons that are being shared assigned to it so it's oxidation number is usually minus two so this is the list of rules for assigning oxidation numbers I'm gonna put this also on C if I hold it here you guys can see it so I'm gonna put this on canvas as well so you need to pause the video and copy this down okay so these are again interview from chem 1a oxygen usually is minus 2 unless it's combined with fluorine or unless it's in the form of peroxide clothing for fluorine iodine they're usually I'm sorry chlorine bromine and iodine they're usually minus 1 unless they're combined at an element that is more electronegative than they are like oxygen so these are the rules that you need to review again pause and write it down now that we know about these rules oxygen usually is minus 2 so minus 2 times 2 is minus 4 so nitrogen must be plus 4 in this case of opposition number of nitrogen so usually I write the totals at the bottom and a single oxidation numbers on the top so here for example for phosphorus but even have ammonium phosphate the oxidation of our phosphorus is the same whether you have ammonium phosphate sodium phosphate or just phosphate ion by itself so an easier way of doing this is to break it up into ammonia oil but a plus one charge and phosphate you remember as a minus 3 charge so oxygen is minus 2 minus 2 times 4 is minus 8 so what should phosphorus be so when I added 2 minus 8 - pretty well it must be plus 5 so phosphorus is plus 5 so that would be the oxidation of our phosphorus and then finally in here I'm going to use this to figure it out so oxygen is more electronegative than carbon so I'm going to assign these electrons away from it it's more electronegative than hydrogen so I'm gonna site these electrons to it and then we decided carbon I'm going to break it so one electron to this carbon one electron to that one so here I had one two three electrons carbon new usually has four valence electrons it's a very upset group four so now it has three cell oxidation number of carbon is plus one because it has lost one electron so now with the oxidation number of carbons in this situation this is just the underlining so you don't count the trans electrons that's just on your life and then one last thing what if I was doing potassium dichromate and I wanted to figure out the oxidation number of chromium so again I break this up into potassium ion and dichromate ion the de- to charge so oxygen again is minus 2 minus 2 times 7 is minus 14 so what should the two chromium's together be so when I added to minus 14 I get minus 2 so it must be plus 12 plus 12 minus 14 is minus 2 which means each chromium is plus 6 because it's plus 12 divided by 2 and so when they saying what is oxidation or if that element it's just that single element so I put some homework on canvas that you can practice your assignment of oxidation numbers so now going back to that reaction and figuring out what's the oxidation number what's the I'm sorry what's the oxidizing agent what's the reducing agent so in order to do that we need to quickly assign oxidation numbers so hydrogen two plus one charge so it's plus one oxygen minus 2 times 4 minus 8 so minus 8 so this must be plus seven minus eight is minus one over here oxygen minus two nitrogen plus two this is again plus 2 this is minus two so this would be minus six so this must be plus five minus 6 is minus one again the oxidation numbers I'm writing at the top the totals on the phone again oxygen minus two so this is minus two since must be plus two so you try to just plus one so then when I look at this manganese went from plus 7/2 plus 2 so it gained five electrons so the manganese in here Megan it gained five electrons so therefore eight God reduce so since permanganate reduced it is the oxidizing agent so mno4 is the oxidizing agent and the agent is the whole thing usually one element within the agent is the one that be a Sun electrons too in terms of getting it or losing him but it's the whole thing that's the agent so the permanganate is the oxidizing agent look at this nitrogen went from plus 2 to plus 5 so it lost 3 electrons so therefore nitrogen monoxide gas is the reducing agent he's the one that going