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Current time:0:00Total duration:4:12

Video transcript

all right so let's see what this what's going on in this chemical reaction so on the reactant side we have some we have an iron oxide this is ferric oxide right over here reacting with sulfuric acid and it's producing let's see this is ferric sulphate and water and we want to balance this chemical equation and I encourage you to pause this video and try to balance this so I'm assuming you've had a go at it and you might have been able to successfully balance it and if you didn't if you weren't able to successfully balance it one one one one theory of why you weren't able to is because this this sulfate group made things really confusing you have four oxygens seven three oxygens here you have seven on this side then you have four oxygens in the sulfate group here but you have three sulfate groups so this is 12 oxygens here and then you have another oxygen here this seems really really really really confusing with especially with all the sulfate group business and the key here is to appreciate that the sulfate group is it's kind of staying together you can kind of treat it you can instead of just saying hey let's try to balance all of the oxygens you can say let's let's balance the the oxygens that are outside of the sulfate group separately and let's balance the sulfate groups separately and to help our brains grapple with that I'm going to rewrite this chemical equation with the substitution I'm going to say let's say that X is equal to a sulfate a sulfate group so let me rewrite all this business so I have it's nice to have I guess this is close to a rust color it seems appropriate so let's say I have some ferric oxide I'm just rewriting what would I have above right over here ferric oxide plus some sulfuric acid but instead of writing h2 and then writing the sulfate group I'm going to write h2 and then X h2 and then X is going to yield is going to yield ferric sulfate ferric sulfate has three sulfate groups so X is a sulfate group it's going to have three of them ferric sulfate plus molecular plus molecular water and so now even though X represents an entire group we let's treat it like an element and just listen umber of is the same number of sulfate groups on both sides so let's balance this chemical equation so let's start with the iron so over here I have two irons and over here on the right-hand side I have two irons so it doesn't feel like I have to tweak the irons at all now let's move on to the oxygens I have three oxygens here on the left-hand side on the right-hand side I only have one oxygen but I can change that by saying let's have three water molecules so then s is going to be three right over here and now let's focus on the hydrogen's focus on the hydrogen's I have two hydrogen's here and I have six hydrogen's right over here so if I have six hydrogen's right over there how do I get six hydrogen's here well I'll have three molecules of sulfuric acid each of them have two hydrogen atoms so now I have six hydrogen's so my hydrogen's my irons and my oxygens that are not part of the sulfate group are all balanced now let's see if the sulfate if we can balance the sulfate groups so on the left hand side I have three sulfate groups let me do that in that magenta color so I have three sulfate groups and on the right hand side I also have three sulfate groups so I'm all balanced and if we want to unsubstituted go back up here okay we didn't change the coefficient on this molecule on the ferric oxide we did change the coefficient on the sulfuric acid we say we have for every molecule of ferric oxide we have three molecules of sulfuric acid we didn't change this they're going to yield one for every one molecule of ferric oxide and three molecules of sulfuric acid it's going to yield it's going to the products are going to be one molecule of ferric sulfate and three molecules of water and we are done