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Current time:0:00Total duration:6:16

Video transcript

alright I'll tackle in the last video we did the first part of Part A now to the second part of Part A so the second part of Part A they say calculate the number of moles of ethene that would be produced if the dehydration reaction went to completion well this is the dehydration reaction right over here and they're telling us they're telling us that we start with zero point two zero zero grams of ethanol so if we start with zero point two zero zero grams of ethanol and if we figure out how many moles of ethanol that is well for every mole of ethanol if we have the reaction go to if the dehydration reaction goes to completion for every mole of ethanol that we start with we're going to have a mole of ethene and a mole of water so if we can just figure out how many moles of ethanol this is then we'll say okay if this were to completely react we would have that many moles of ethene so let's figure this out so if we say so we have ethanol so for ethanol we are starting with zero point two zero zero grams and we want to convert this to moles so we want to multiply this times we want grams in the denominator to cancel out with this grams and moles in the numerator so one mole of ethanol is as a mass of how many grams well they tell us that earlier on the problem they say ethanol molar mass forty six point one grams per mole so ethanol molar mass of forty six point one grams per mole or another way to thinking about it one mole would have a mass of forty six point one grams and so if we do this we are going to get zero point two zero zero over forty six point one and then grams cancel with grams and that's going to be how many moles we have and this is going to be equal to we have three significant digits that we're going to be dealing with three significant digits divided by three significant digits so this is going to be all right so let me clear this so 0.2 I could write zero zero but it's going to for the calculators purposes it's the same thing divided by forty six point one is equal to zero point zero zero four three I want three significant figures here so for three I'm going to round up for three four point zero zero four three four so zero point zero zero four three four moles so what we've seen so far if the ethanol were we the reaction if we have this many moles of ethanol well if we and if they completely react well that we should end up with that many moles of ethene and so in if we have if we could say dehydration let me write it this way if dehydration dehydration reaction goes to completion goes to completion every every mole of ethanol ethanol would be converted converted to a mole of ethene and a mole of water I shouldn't write the shorthand there a mole if I'm writing it out mole of and a mole of water so so zero point zero zero four three four mole of ethanol would yield that same number of moles zero point zero point zero zero four three four moles of ethene so if the reaction went to completion that's how many moles you would produce what we actually measure is a smaller number than that so the reaction and go fully to completion so now let's tackle Part B let's tackle Part B and they ask us calculate the percent yield of ethene in the experiment well that's the percent yield is if is going to be how much we got divided by how much we would ideally have gotten if the reaction went fully to completion so yield yield is going to be equal to how much we actually got which we figured out in part one so zero point zero zero two six four moles over what we actually got or so what we actually got over what we would have ideally gotten if the reaction went to completion so divided by zero point zero zero four three four moles and this is going to be equal to this is going to be equal to so zero zero two six four divided by zero zero four three four is equal to and let's you have three significant digits here so sixty I could say point six zero eight or I could say sixty point eight percent yield so I could write this as actually it's going to I'm rounding so I could say is 60.8% yield and there you go
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