Answer to Question #33742 in Inorganic Chemistry for raj

Question #33742
how many moles and molecules of o2 are there in 64g of O2 .What is the mass of one molecules of O2?
Expert's answer
Moles are in O2 in 64 grams:
n = m/M
= 64g/32g per mol
= 2 moles
Molecule of O2 consisy of 2 anoms, then:
64 g x 1 mol/ 16 g = 64 mol / 16 (grams cancel)
64 / 16 = 4 mol
Then in order to find molecules you need to know avogadro's number, which is basically just the definition and value for the unit mol.
avogadro's number states that
1 mole = 6.02 x 10^23
so, we use a conversion factor again to find how many molecules are in 4 moles.
4 moles X 6.02 X 10^23 / 1 mole = (moles cancel)(multiply 4 and 6.02) = 24.08 x 10^23
You need to move the decimal point so that the number is between 1 and 10. So we move the decimal point once space to the left to create: 2.408 The exponent also needs to change from 10^23 to 10^24 to account for the decimal place we moved. So, in 64 grams of oxygen there are 2.408 x 10^24 oxygen molecules, you should probably just write this answer as 2.4 x 10^24 because this accounts for the significant figures you started out with (you had 2 when we started out with the molar mass of oxygen @ 16) and now, we have two again.

Answer: 2.4 x 10^24

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