Composition

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##### Top Chemistry 101 Educators ##### Stephanie C.

University of Central Florida ### Video Transcript

right. So we have six compounds here, and we're to find each of their massive moles a number of molecules given only one of those values. So in order to do to fill out this table, we require some formulas. Okay, So in order to find mass, we need to take the moles and multiply it by moulder mouths and to find malls for you want to rearrange this formula for moles and multiply or divide by Mullah Mass on both sides. Divide you would get malls is equivalent to mass over more mess. Okay. And to find a number of molecules, we just have to take our moles and multiply it by Have a gorgeous number. No, Nas and a its symbol Navajos number or constant is, if you remember 6.2 to times 10 to the 23. So a very large number and it's in units of her more. All right. And if you wanna rearrange this formula to sulphur Mel's you could take you would divide by any avocados number on both sides that would give us moles equals molecules. Molecules over Have a god rose constant. Okay, so these four equations are all we need basically two equations with with their alternative rearrangements to fill out. Well, these are the only ones of me to fill out this on chart. So I also have listed molar mass here on this bottom row to help us, you know, salts on the way, calculated Mullah. Massive. All of these elements was by, um, calculating or summing up the individual molar masses of each element. And Adam, even in this in these compounds. So first up, we have benzene or see 686 to solve for moles. We would use this formula because you're only given mass and molar mass. So we just make that simple division and we get zero 0.54 then to sell for a number of molecules we would use This one is formula and take the than member of balls we found keeping your calculator and multiply it by avocados constant. And you can calculate that. But before I continue, I just want to quickly explain what E is going to meet. So e is equivalent to times tend to the exponents because when we start talking in a number of molecules, warranted start to need in the kind of notation to, you know, accommodate those very large numbers. So E signifies times tend to be exploited. So once you've taken this number of most multiplied by avocados number we get 3.3 times 10 to the power of 22 to the exponents 22 or eat attorney to yeah to okay, water pistol for mass. We used this formula and take these number of moles, multiply it by the molar mass and we get for went 003 To find number of molecules, we take the number of moles and multiply it. But I have a gorgeous number and promote Olso most intense well, and we would get 1.35 times 10 to the 23. Next, we have carbon dioxide. So that's first cell from walls to solve from malls. There's two equations that we have here because we have number of molecules will just take number of molecules and divide it by our god just number. Take this number divided by six to the 23 and we get is your 0.45 And to find mass, you multiply number of moles by molar mass seen in this patient and we get when appointing I need way have hydrogen chloride in this column, so to sell for mass. Same thing. Multiply moles by molar Mass. Can we get 45 flint mine To find a number of molecules to take moles small number and get 7.62 23 e to 23 or times 10 to the exponents. 23 Water again to solve for moles will take a number of molecules divided by a guard. Just number. When we get 6.9, then my mass. We take this number, moles a multiply it by more mass. We get one point grams. Units are all over here, grams. Most number is a night. Okay, last one or here is methanol or sees three village just off from walls. We'll take this formula mass over molar mass that gives us small number nine 0.3 times. Tend to the negative three on a space. And this isn't saying that this number is negative because that wouldn't make sense to have negative number of moles. But it's saying that it's a very tiny number, and lastly, to find molecules number volunteers will take this very tiny moles multiplied by have a garters number, which gives us 5.6 times 10 to 21. All right, just to clarify this formula over here, it says, um, molecules. And in on the last video, it says that n times an A equals Adams, but in reality equals, it does equal molecules. It's just that when we have an elemental entity like metals just caused hume or iron, the number of molecules does equal the number of Adams. So this quote equation is you is the most direct one. So to find number Adams, you just need to, you know, multiple how many atoms are in an individual molecule, so yeah. McMaster University

#### Topics

Composition

##### Top Chemistry 101 Educators ##### Stephanie C.

University of Central Florida 