Molar Conversions: Grams to Moles and Moles to Grams


Okay in this video today I’m going to show you how to do molar calculations and molar conversions and we’re gonna be showing you how to calculate from grams to moles and moles to grams. Now the first thing you have to remember when you calculate from grams to moles or moles to grams you have to use the
molar mass of the compound that you’re trying to convert. So here I wrote the generic form for the molar mass: 1 mole is equal to X number of grams. You need to remember that every compound has a different molar mass and before you start you actually have to calculate the molar mass. Now, before in the previous video I showed you how to calculate the molar mass and so for this video I’m just gonna write them down. Here for the first problem we have Magnesium Hydroxide; the molar mass of Magnesium Hydroxide is 1 mole equals 58.32 grams I recommend that when you do these calculations from grams to moles or moles to grams that you right down the molar mass in this form. 1 mole is equal to 58.32 grams because that is going to be our conversion factor. That is what we’re going to use to convert when we convert from grams to moles and moles to grams. Okay? So let’s go ahead and do a couple problems. The first thing I recommend people do is this: read the problem. How many moles are there in 30.10 grams of Magnesium Hydroxide? Now you need to think about what have you been given, and what are you trying to find? Obviously you’ve been given, and I put a little “G” here, 30.10 grams and you’re trying to find out how many moles. Okay I think it’s a good idea to
mark those down because the first thing you’re going to do is you’re going to write down what you have been given. So let’s write it down we have been given 30.10 grams. Just write that down; just follow the steps, basic steps write it down. Multiplication, your division line for your conversion factor. Now one thing you need to remember is you’ve been given grams, our molar mass is 1 mole in so many grams, if we have grams here in the top of this fraction so to speak, then we know that we’re automatically gonna put the grams in the bottom. We don’t really have to think about it
too much, we just put down 58.32 grams. And then the other for conversion factor goes on the top, that being 1 mole. You will see we want to find
out how many moles we have; we’ve been given grams our grams will cancel like this, we’re left with moles and if we multiple 30.10 by 1, divided by 58.32… we end up with 0.52 moles okay? That’s all there is to it it’s not that
complicated just try to follow the steps figure out what is you’re trying to find, what you’ve been given, write the thing down that you’ve been given, you’ve been given something in grams therefore the conversion factor part of your molar mass goes in the bottom for grams so you can cancel and then you’re left with moles. Alright? So that’s the first one now let’s do one where we convert back the other direction. Now this time we want to know what is the mass. So what what is the mass we’re trying to find, put a little “F” there for what we’re trying to find, we’ve been given some number of moles of Calcium Chloride Dihydrate so I’m gonna put down the given like that. Now once again I don’t think about it too much, just write down what I’ve been given like that. I was given 1.75 moles. I’m going to put down my division, my multiplication sign, my division bar,
and the molar mass of Calcium Chloride Dihydrate is that one mole is equal to 147.02 grams. That’s my conversion factor. That is what I’m going to use to convert from moles to grams. Now you’ll see this time I have moles over here. In this case I had grams, I put grams in the bottom. I have moles here therefore I’m just going to automatically know that 1 mole goes on the bottom. That is going to allow me to cancel, but I put my 147.02 grams, my molar mass, like that. That is the number of grams in 1 mole and then I end up with an answer that is 257.29 grams. You can see once again models cancel, I’m left with grams, I want to know what is the mass, that is my mass. With this problem I wanted to know how many moles, that’s my moles. Now you should notice that in each case you have your value over here that you’re given it’s either gonna be 1 mole divided by the molar mass or in this case because I’m given moles it’s the number of grams in 1 mole over 1 mole. So you can see I just switched these 2, here I had moles at the top and grams at the bottom In this case I had moles on the bottom and grams on the top. Okay, that’s all there is to it, follow those steps and I think you’ll be very successful. Thank you!

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