Module 5 Lesson 2 Benjamin Huffstetler

Updated: 7/21/2020

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- Did ya'll understand the percent composition by mass that we went over today in Chemistry?
- Yes, I think I do. Let's go to Mrs. Clemmer's class and I will explain it.
- Water has two hydrogen molecules and one oxygen molecule. We can figure out the molar mass of water by using the masses of Hydrogen and Oxygen.
- Let's use the element H20 as an example.
- Hmmm...so water has two hydrogen molecules and oxygen has one.
- Yes, me too.
- Thanks, Brent. I think I have it now.
- There is a couple things you should remember.
- There are a few steps to finding the percent composition. The first step is to find the mass of the elements in the compound, for example H20.
- There are 2 masses in H20. There is hydrogen with an atomic weight of 1.00794 and oxygen with an atomic weight of 15.9994. When you add the atomic weights together your molar mass comes out to be 18.01528.
- There are a few things that you need to remember when finding the percentage. The equation is (Mass/Molar Mass) * 100. So for Oxygen it would be (15.9994/18.01528) * 100, which equals 88%. For Hydrogen, it would be (1.00794/18.1528) * 100 to get 12%. This proves that water consists of 12% Hydrogen and 88% Oxygen. You can double check yourself by add the numbers up. If they equal 100, then you are right.