How many moles of O atoms are there in 157.4078 grams of KMnO4?

Question

How many moles of O atoms are there in 157.4078 grams of KMnO4?

Answer= 3.985007595

Now if your lab partner determined that there were 6.528 x 10^20 atoms of O in an unknown sample of KMnO4, how many milligrams would the unknown sample weigh?

Answer 1

find moles of oxygen withAvogadro'ss #:

6.528 x 10^20 atoms of O @ 6.022e23 atoms /mole = 1.084e-3 moles of oxygen

find moles of KMnO4:

1.084e-3 mol oxygen @ 1 mol KMnO4 / 4 mol O = 2.710e-4 moles of KMnO4

find grams of KMnO4 using its molar mass:

2.710e-4 mol KMnO4 @ 158.0grams / mole = 0.0428298 grams KMnO4

times 1000 mg / gram =

your answer: 42.83 milligrams KMnO4