How many grams are there in 9.4 x 10^25 molecules of H2?

Question

I know that the problem should be solved by dividing it by Avogadro's Number.  I'm confused about that part because my calculator matched the answer my computer calculator got (for this and several similar questions), but it's not correct.  I get 1.56 x 10^48 x 2.02.  However I know that's not right. What am I doing wrong?

Answer 1

You start with 9.4 x 10²⁵ molecules of H₂.

You know that an Avogadro's number of molecules of H₂ has a mass of 2.0 g.

 

To solve, 9.4 x 10²⁵ molecules H₂ x (2.0 g H₂ / 6.023 x 10²³ molecules H₂) = 312. g H₂

Answer 2

First you want to use Avogadro's number to convert the number of molecules to moles

Moles = Number of Molecules / Avogadro's Number

Moles = 9.4 x 10^25 / 6.022 x 10^23 = 156.09 mol

From there then you want to convert that over to grams by multiplying by the Molar Mass

156.09 mol x 2.016 g/mol = 314.69 g

meaning that there are 314.69 grams in 9.4 x 10^25 molecules of H2