Compound X, isolated from lanolin (sheep's wool fat), has the pun...

Question

Compound X, isolated from lanolin (sheep's wool fat), has the pungent aroma of dirty sweatsocks. A careful analysis showed that compound X contains 62.0% carbon and 10.4% hydrogen. No nitrogen or halogen was found.

b. A molecular weight determination showed that compound X has a molecular weight of approximately 117. Find the molecular formula of compound X.

Accepted Answer

Hey everyone, let's solve this problem. It says compound a is a compound found in Goat's milk. A careful analysis showed that compound a contains 42.11% carbon and 6.48% hydrogen, no nitrogen or halogen was found determine The molecular formula of compound a. If the molecular weight analysis showed that compound a has a molecular weight of about 342 g per mole. Okay, well, the problem says we are determining the molecular formula of compound A. I'm going to sort of work backwards and look at what we were given and try to connect those two with some middle steps here. Let's try and figure out the steps of how to get from point A. To the end of this problem. Let's say point B. I guess so, if we're looking for the molecular formula, what do we need? Well, we know that the molecular formula shows the molar ratio of each element in the compound. So if we're looking for the molar ratio, we need to know the number of moles of each element in one mole of compound. A. right, okay. And how do we do that? Well, I could get the number of moles from an amount. Right. Say if I had grams of each element grams of each element in this is going to be a step number. I don't know what step number yet. So grams of element I can convert that to moles. Right. Using a molar mass. Okay, well, was I given the grams of the element in each in compound A No, that would be too easy. Right. But I was given percentages. So let's go to step number one. Well, I have 42.11% carbon plus 6.48% hydrogen. Does that equal 100% for compound a. No. Right. Well, I can see by the answer choices that I have some oxygen in here and they tell me that there's no nitrogen or halogen. So we need to find out that percentage of oxygen. Okay. And we can do this with some simple algebra. Right? Just subtract the sum of carbon and hydrogen from 100. Okay. Okay. Well if I find out the percent, if I have the percentage of each element, then I could find the grams of each element. If I have the grams of compound A. Do they give me a specific weight or amount of compound A that we're looking at? No, but we're given the percentages. So it doesn't really matter. Right? We can just make one up. So let's assume That we have, let's say 342 g Of compound a. And why did I pick that number? Because that will equal one mole of compound a. And that will make our numbers even when we sell for the number of moles of each element. So assume 342 g of compound a. Because that's one mole of compound a. Okay. So then once we assume that total amount we can find the amount of carbon, hydrogen and oxygen in grams right grams of each Element using those percentages that we just had in step one and look at that. That will lead us to what will be step three. Right? If I find the grams of each element, I can convert them to the moles using their molar mass, which then will help me find the molecular formula. Does that all make sense? Well, if it doesn't keep watching and I'll show you how it's done. But I hope that makes some sense. Alright, so first We're going to solve for that percentage of oxygen. So then we can move on to step two. So I'll take my 100% the percentage of carbon, 42.11 minus the percentage of hydrogen 6.48 And that equals 51.41% of oxygen. Okay, so I have my three percentages here. And I guess I should write carbon and hydrogen. Alright, so now we can multiply those percentages by our 342 g of compound a So carbon Will be 342g of compound a times .4211 Will give me 144g of carbon. Okay, hydrogen is 6.48. So multiplied by . 6.48%. I mean so multiply that by .0648. We get 22g of hydrogen And oxygen is 51%. So we multiply by .5141 And that gives us 175g of oxygen awesome. So now we found our amount, theoretical amount of each element In one mole of compound a So now we're looking for our molar ratio. So let's find out how many moles each of these uh converts to. Since we know they're in one mole of compound A We can just simply convert them to moles. So 100 and 44 g of carbon divided by the molar mass of carbon, Which is 12 g right per per mole of carbon. and a ratio to hydrogen which is 22g of hydrogen divided by one g per mole of hydrogen. And our ratio of oxygen which is 175 g of oxygen divided by 16 g per mole of oxygen. So we're dividing by the molar mass to convert to moles, which if you do the maths, you get 22 and 11. So, if we write this in our molecular formula, that would be C. 12 H 22 0 11. Alright. And we see that this is answer choice C. Okay, so answer choice. C. Will be the correct answer. And I hope this video is helpful. Thanks for watching

Watch next