Question

How many moles of water, H2O, contain 2.0×1022 molecules of water? (See the hints for assistance in interpreting scientific notation.)

Express the quantity in moles to two significant figures.

Answer 1

In this question, what are we really being asked? We are being asked about the number of moles there in 2.0x10^22 molecules of H2O.

We are going to use the formula,
Number of moles = Number of molecules / Avogadro's number

We have the number of molecules: 2.0 x 10^22
Avogadro's number: 6.02 x 10^23

Now we will plug in our information in a scientific calculator:

(2.0 x 10^22) / (6.02 x 10^23) = 0.03 moles is our answer.