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Carleton College

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University of Kentucky

University of Toronto

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So in the previous video, we figured out the molecular weight of each molecule and atomic mass units. And we did this based on the atomic fast units of each atom. So in this video, we will be using the molecular weight information to obtain the molecular composition or the weight composition of each molecule. And again, this is based on the atomic mass unit. And we'll be using the examples from the previous video, um, to kind of illustrate how these concepts are connected. So in our first example, um, we looked at water, which has a molecular formula of H 20 And we figured out that hydrogen has an atomic mass unit of one point 01 I am used and oxygen has an atomic mass units of 16.1 AM use, and we determined that the total wait is 18 0.2 can use. And so to figure out the percentage composition, you can kind of think of it as if you were trying to figure out a percentage, Um, for let's say, the number of colored balloons they have at a party. So let's say you have 100 balloons and you have 20 red balloons and 80 blue balloons. So the percentage of blue balloons is 8/10, which is 80% and red is 20% because that's 20 over 100. So we're kind of using a similar concept to figure out the percentage composition of each molecule. So first, let's calculate it for hydrogen. Um, so for 100 of what you do is you need to do a ratio off the total number of hydrogen atoms in the molecule over the total weight. So here it would be, too times 1.1 Because we have to hide regions. And each region has an atomic mass unit of 1.1 and the total wait is 18 0.2 So then, if we determine this ratio and converted in 2% um, this ends up being 11 point to present. Now, if we look at oxygen, we only have one auction, Adam, so we can just write its atomic math unit, which is 16.1 and we can divide that overthrew the total weight of the molecule. And so if we convert this into percentages, this actually comes out to be 88.8% and a good way to check your answers is to make sure that the percentages add up to 100. And in this case they do so your final answer would be that water is made of 11.2% of hydrogen, Um, and 88.8% of water is oxygen. So going to our next example sodium chloride again, we found out that a single adam of sodium has Atomic Mask Unit 22.99 and chloride has an atomic mass unit off 35 0.45 and the total weight is 58 0.45. Amy's so using the same strategy as before, we will figure out the percentage composition for each Adam in our molecule. So for sodium, we only have one sodium atom, which has an atomic mass of 22.9, a weak and divided over its total mass, which is 58 0.45. And if you simplify this ratio and converted into present, this actually ends up being 39 point represent. And if you do the same thing for Florida, um, the atomic mass off ride is 35.45. And if you divide this by the total weight, which is 58 0.45 and simplify the ratio and convert this to 8% you get 60.7%. And so, if we add these breast savages together, you do get 100 eso. Your final answer is that sodium fluoride is 39.3% sodium and 60.7% correct. And so, for our final example, sugar, we know that sugar again is actually seeing 12 page 22 11. And it is made up of carbon, hydrogen and oxygen. So carbon has an atomic mass unit of 12.1 for ha jin, this is 1.8 and for oxygen it is 16.0 AM use and the total weight. Well, sugar came out to be already down here 34 342.2 atomic mass units, and so sure has three atoms and not to atoms. So again, you want to make sure that you account for all the atoms in your modules. And so, again, using the same methods as before, we'll calculate the percentage composition. So there are 12 atoms of Carmen your molecules. So you want to make sure that you multiply 12 by 12.1 and divide this by the total weight, which is 342.2 a muse. And if you calculate this, this ends up being 42.12% and moving on to our next Adam. There are 22 atoms of hydrogen in this molecule, and so you want to multiply this by one point 008 and divide this by the total week, which is 342.2. And if you do out the math, this should equal 6.480%. And finally, for oxygen we have 11 atoms of oxygen, so you need to multiply 11 by 16.0 which is theater Tomic, mass. Unit of a single oxygen. And divide this by the total weight, which is 342.2. Amy's And if you do about the math, you end up with 51.40% and again. When you want to check your answer, you want to make sure that the percentage is that you get some up to 100. So if you add these together, they dio so these are your final answers. Eso This tells us that sugar, um, is composed of 42 0.12% carbon, 6.48% hydrogen and 51.4% Austin.

Brown University

Aqueous Solutions

Thermochemistry

Electronic Structure

Periodic Table properties

Chemical Bonding