In today's class, we went over the percent mass of elements in compounds and did a few examples.
The percent composition: the percent mass of each element in a compound
How to find the percent composition:
1. Find the total molar mass of the compound.
2. Next, find the molar mass of each element. (Remember, if there is a subscript, you must multiply the element's mass from the Periodic table by that subscript.)
3. Finally, divide each element's molar mass by the toal molar mass.
Note: Do not round right away to a whole number!
ex. (from in-class) Find the percent composition of K2Cr2O7
step 1: 2(39.10) + 2(52.0) + 7(16.0) = 294.2 g/mol (the total molar mass)
step 2 & 3:
2(39.10) ÷ 294.2 g/mol = K 27%
2(52.0) ÷ 294.2 g/mol = Cr 35%
7(16.0) ÷ 294.2 g/mol = O 38%
ex. What is the percent of carbon in glucose, C6H12O6?
step 1: 6(12.0) + 12(1.0) + 6(16.0) = 180.0 g/mol (the total molar mass)
step 2 & 3:
6(12.0) ÷ 180.0 g/mol = C 40%
Here's a video to recap! Enjoy!
0 comments