Question

How many grams are there in 2.8 * 10 ^ 24 molecules of Li 2 O?

Answer 1

First, we must know Avogadro's number:

1 mol of any substance = 6.02x10^23 formula units (ions, atoms, molecules, etc)

Also, we can say this:

1 mol of Li2O = its mass expressed in grams

(from Li2O molar mass = 30 g/mol approx.)

Now,

1 mol Li2O = 30 g = 6.02x10^23 molecules Li2O

30 g Li2O ----------- 6.02x10^23 molecules Li2O

x ----------- 2.8x10^24 molecules Li2O

x = 140 g approximately

Answer: 140 g