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Avogadro's Number

Avogadro's number, also called Avogadro's constant, is the number of constituent particles, usually atoms, molecules, or ions, that are contained in the amount of substance given by one mole. One mole of a substance has a mass in grams equal to its molecular weight in daltons.


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Video Transcript

So before I begin this video, I wanted Thio briefly correct myself in last video eso last time I think I reported water in five significant figures, but it should be four significant figures eso this video I will be using the value 0.1723 miles, Right? So last time we figured out how to calculate the molar mass of the different molecules in this combustion reaction of sugar. And we've also figured out how to calculate to the number of moles of each molecule given the mass of sugar. And so in this video will be learning how to calculate the number of particles or, in this case, the number of molecules, um that are produced in this reaction based off of the previous information from the last video. And so we can do this by using avocados number. And you might remember this, um, in the dimensional analysis video that I did previously. So Allah, God Rose number just all right. On the side is six point 0 to 2 times 10 to the 23rd particles Permal and avocados. Number is basically a way for us to convert moles to number of particles on DSO will be using this to calculate the number of molecules given the number of moles for all of these molecules. So to do this we'll be using dimensional analysis again. And so we could do this by beginning to write the value that were given first. So here we're working with the moles that we calculated from before, and you calculate the number of molecules, Um, in the given number of moles will be multiplying This by Allah. God, Rose number has shown here, and I don't have all of states. So I'm not gonna write particles, but make sure that you keep in mind that this is in particles. And so again, if we use dimensional analysis, we can cross off the bulls. And is this ensures that we have the right answer, which is a number of particles. And so what do we do out the math? We should get nine 0.430 times 10 to the 21st molecules. And so, given 0.1566 moles of sugar, we have 9.430 times 10 to the 21st molecules using avocados number and again, you can do the same thing for oxygen, carbon dioxide and water. And so we already accounted for the fact that they're 12 molecules per one molecule of sugar in the previous problem. So now we just need to multiply this by Alpha God Rose number. So again, using dimensional analysis, you can multiply this like so. And instead of what about the whole thing? I'll abbreviate this as a hashtag, and so this will equal 1.132 times 10 to the 23rd. And given that we're using the same goals for carbon dioxide, this is also 1.132 times 10 to the 23rd molecules. And you want to make sure that you always keep your unit straight. Yeah, raised. Well, um, you'll be multiplying avocados number by a different value. And so it would be 0.17 to 3 times all cadres number, which ends up being 1.37 times 10 to the 23rd. And again, I'm making sure that I'm keeping my significant figures the same throughout the whole problem. And so now we've calculated the number of molecules for all the molecules in this combustion reaction And so now, in addition to calculating the number of molecules, you can also calculate the number of atoms. So, for example, let's say you're given a mass, and you want to calculate the number off carbon atoms that you're using in this reaction. So before you can use 3 g that you're given to calculate the moles, and then you can use that to calculate the number of molecules for the sugar molecule. So now, if you want to calculate the number of carbon atoms, you would basically multiply this by 12 because there are 12 carbon atoms. So if we do this out, this is me 12 times nine point 430 times 10 to the 21st. And so you would get 1.132 times 10 to the 23rd carbon atoms for sugar. And so here we can see that you can use avocados number to calculate the number of atoms or the number of molecules, depending on which when you're looking for, by using all of this information, and this will be very useful when you're trying to get quantitative information from chemical reactions. And in the real world, um, we actually use this a lot in synthetic chemistry because there are some reactions that require specific ratios off molecules. Thio obtain the number of product that you want, and so it's important to understand how to do all of the story count entry. So you end up not wasting any precious material to create your product or if you just want to have a small scale reaction to make sure the reaction works in the first place and has a good yield. Or if you want to set up some kind of reaction on a larger scale because you want a lot of starting material for something a bit more complicated.