3.00 moles of NO2 have a mass of

When solving for the mass of a compound when you're given the number of moles present, you need to know the molar mass (how many grams there are in a mole of that compound).

In this case, we can make the following equation:

3.00 (14.01 + 2 (16.00))

In Nitrogen, the molar mass is 14.01 grams per mole, and Oxygen is 16.01 grams per mole.

However, because there are 2 oxygen atoms present per molecule, you must multiply it by two in order to solve for the molar mass.

Anyway:

3.00 (14.01 + 2 (16.00))

Simplify:

3.00 (14.01 + 32.00)

3.00 (46.01)

Multiply:

3.00 (46.01) = 138.03

3.00 moles of NO2 has a mass of 138.03 grams.

-T. B.