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Very Common Mole Questions

Feb 23, 2020
In this video I want to talk about two

very

common

types of

questions

about

mole

s. These two types of

questions

don't really fit into the other categories we've talked about. Do they appear all the time in assignments, in textbooks, in quizzes, and particularly? in tests and exams ok here is the first one what is the mass in grams of a single atom of oxygen ok this is a type of question that asks us to calculate the mass of a single atom of some element here we are going to use oxygen As an example, now To solve problems like this we have to get some different data about

mole

s.
very common mole questions
Well, the first one will be about mathematics. Well, we're talking about the mass of a single oxygen atom. What do we know about the mass of oxygen? Well, we can look up oxygen on the periodic table and we can zoom in on this number 16.00 which tells us the molar mass of oxygen, it tells us how much one mole of oxygen is equivalent to in grams, so we can say that from this information on the periodic table , 1 mole of oxygen atoms equals 16.00 grams, okay, but we're not talking about one mole of oxygen atoms, we're talking about a single oxygen ad, one oxygen atom, so what do we know about let's say , such as the number of oxygen atoms in a container, you may know that one mole of oxygen atoms contains 602 hexadecimal oxygen atoms which we often abbreviate is six point 0 2 times 10 to the power of 23, now we want to combine these two data .
very common mole questions

More Interesting Facts About,

very common mole questions...

To make a third piece of information, ok look at this, we know two things here, on the one hand we know that one mole of oxygen atom of oxygen atoms is equal to 16.00 grams and we also know that one mole of oxygen atoms It contains 602 hexadecimal oxygen atoms. So we can combine these two pieces of information to say that 602 xylion oxygen atoms are 16.00 grams. Ok, we can even take this and express it as an equation, as a relationship, here we can say six point 0 2 times 10 to the power of 23. oxygen atoms equal or equal to 16 grams now look at this last one that I drew well, this here is a equation a relationship that we can convert into a conversion factor that will allow us to go from the number of oxygen atoms we have to two grams Okay, so I'm going to use this equation as a conversion factor to go from one oxygen atom to a certain amount of grams.
very common mole questions
This is how I'm going to do it. Let's start here. I'm going to make an oxygen atom and now I'm going to multiply that by a conversion factor made from this relationship. I want to get rid of the oxygen atoms at the top here, so I'm going to write this ratio as a conversion factor with the oxygen atoms at the bottom. Well then. I'm going to take this part here 6.02 times 10 to the 23 oxygen atoms, I'm going to put it on the bottom and make my fraction here a little bit longer and then I'm going to put the other side of the ratio 16.00 grams on the top and now when I work through the calculations here, the oxygen atoms at the top, the oxygen atoms at the bottom will cancel out and that will leave me with grams, which is exactly what I want, I'm just going to rearrange this so we can go over the calculations, okay?
very common mole questions
If you write this down, you probably want to figure it out by putting it on your calculator. You can write it like this, although you don't actually have to multiply by one here because multiplying something by one doesn't change its value, but it totally does. it's up to you to put this in your you're going to get this as an answer this e-23 and calculator language just means this multiplied by 10 to the power of negative twenty-three and then we're going to want to take this number and round it to three significant figures we don't worry for the significant figures in one here because this is a counting number, we are saying that an oxygen atom is not a measurement, so it has an infinite number of significant figures, we will round it to three significant figures because there are three and six point 0 2 which has a smaller number, so you can set, so we round this to two points, we have the five here, we round it up because the 72.6 six times ten to negative twenty-three and what are our units.
They are grams, that's what we were left with after the conversion factors. Here is our final answer in scientific notation and if we write this in regular decimal notation we can see that it is a tiny tiny number two point six six times ten at negative 23 grams so the mass of a single oxygen atom is fine, so the The key to solving that problem is being able to take this information and write conversion factors with it, okay, we knew that a mole of oxygen waits that long and we know how many oxygen atoms are in a mole, so we could take that information and write these two conversion factors.
This could allow us to go from the number of oxygen atoms to grams and back and forth what mass of mercury has the same number of atoms in 64.2 grams of calcium. I don't know about you, but I find the wording of this question really confusing, so I want to try to explain what you're really trying to ask here so you can understand how to solve it. Well, we have mercury and calcium. we can look them up on the periodic table and this number here, the molar mass, tells us how much one mole of each of these types of atoms would wet.
So here we know that one mole of mercury atoms, 602 xylons of mercury atoms, would weigh 200. point 6 grams and for calcium here one mole of calcium atoms 602 heck silicon calcium atoms weighs forty point zero eight grams well, so here's the main point the main point is that 200 point six grams of mercury and forty point zero eight grams of calcium both have the same number of atoms okay the masses are different this weighs a lot more it's a lot more light, but the point is that, although the masses are different, the number of atoms is the same: 602 atoms of hexylene mercury weigh as much and 602 xylon calcium.
The atoms weigh so much, so we can say that this amount of mercury and this amount of calcium have the same number of atoms. Well, what really begs the question is something like X grams of mercury and 64.2 grams of calcium have the same number of atoms. atoms right, that's not really a question, but it's a statement, okay, it's like how much mercury has the same number of atoms, 64.2 grams of counts, well, this amount of mercury and this amount of calcium have the same number of atoms, this amount of calcium and how much mercury has the same number of atoms, so this is how we are going to solve it, we can do two steps, the first step we are going to ask how many atoms are there in 64.2 grams of calcium and then we are going to take that number of atoms that are in this amount of calcium and we are going to ask if we had that number of mercury atoms, how many would there be?
So let's start here with the first part. Okay, I'm going to start here with 64 points. grams of calcium and now I want to know how many atoms there are, so I'm going to multiply it by a conversion factor that I can make from this information. Here I want to get rid of the grams, so I'm going to put grams. At the bottom I'm going to do 40 points, 08 grams of calcium and then at the top I'm going to put 6.02 times 10 to the power of 23 atoms, okay, now we have grams of calcium here, grams of calcium here, they're going to Cancel.
I'll stick with atoms, calcium atoms. I can put this in the calculator. I get it as an answer. I'm going to round it to three significant figures, so I'm going to nine point six four times 10 to the 23, okay, 9.64 times 10 to the power of 23, calcium, of this, how many calcium atoms is not that much calcium? Now the next thing I want to do here is ask if we had that number, if we had this number of mercury atoms, how? How much would be good like this? So we have that many calcium atoms if we had that amount of mercury.
How much would be good like this? So this is how we do it, we're going to take this and we're going to multiply it by a conversion factor. which we can write from this information that tells us how much a certain number of mercury atoms is, so we're going to multiply that by six point 0 2 times 10 to the power of 23 and make hg mercury atoms at the bottom and then multiply I reduced it to 200 point six grams of mercury at the top and now the mercury atoms at the top, the mercury atoms at the bottom cancel out that I have grams of mercury left, the calculations that I am going to do are these, I pull this out of the calculator and My final answer rounded to three significant figures is 321 grams of mercury and that tells us how much mercury, what massive mercury would have the same number of atoms as 64.2 grams of calcium.

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