How many moles (of molecules or formula units) are in each sample

18.4g NO2
1.48kg CO2
32.4g KNO3
152.4kg Na2SO4

please help me! please at least explain one of these so that i can figure it out! i really do want to understand how to do these. thanks.

I am only showing the first problem
1)to find the mols of a molecule from the grams of the molecule first find the molar mass of the molecule.
NO2 has one one N atom and two O atoms.
one atom of N has the molar mass of 14.01g/mol
one atom of O has the molar mass of 16.00g/mol
Therefore the molar mass of NO2 will be found the following way:
14.01 g/mol of N
16.00 g/mol of O
+ 16.00 g/mol of O
--------------------------------------…
46.02 g/mol of NO2

2) Next, you multiply through
multiply the amount of NO2 given by the molar mass of NO2

18.4 g of NO2 * 1/46.02 mol/g of NO2 = .400 mols of NO2


the problem is setup in the way shown above because you want to get your answer in mols. the grams on the top get crossed out with the grams on the bottom and you get your answer in moles. Divide 18.4 by 46.o2 and you get an answer of .400 mols of NO2.

3) for the following problems, remember to convert kg to g.

You simply divide the amount of the sample you have by the total molar weight of the compound. For NO2, first find the molar weight for one molecule. You do this by using a periodic table...weight of N=14, weight of O=16, but you multiply by 2 so it equals 32. The weight for one mole is roughly 46, so now divide 18.4 by 46, and that is your answer.