Chemistry question with mole problems
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# Chemistry question with mole problems

[From: ] [author: ] [Date: 11-06-28] [Hit: ]
So I got 2.How many moles are contained in 5.29 x 10^9 molecules of soduium sulfite?I got 8.79 x 10^-15 moles for this.I got the right answers but I kinda guessed.......
How many total atoms are contained in 3.2 x10^23 molecules of sodium sulfate?
So I got 2.2 x 10^24 atoms and I have the answer key (THE ANSWERS ARE RIGHT)

How many moles are contained in 5.29 x 10^9 molecules of soduium sulfite?
I got 8.79 x 10^-15 moles for this.

I got the right answers but I kinda guessed...and I'm confused on how it works. For example, since they gave me 3.2 x 10^23 molecules I multiplied that by 7atoms (cause theres 7 in sodium sulfate) and then divided by 1 molecule so they'd cancel out.

For the 2nd problem the problem gave me 5.29 x 10^9 molecules and the multiplied that by 1 mole divided by 6.02 x 10^23....

What I don't understand is why I divided by 1 molecule in the first problem and then 6.02 x 10^23 and the next problem because the given is still the same units (molecules)! Im really confused help D:

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You did the right thing both times. I would say, forget about the units, because there ARE seven atoms in one molecule of sodium sulfate, so if the number of molecules is 3.2 times ten to the whatever, then the number of atoms HAS TO BE 7 times that. But if the units really bother you, the reason that the units cancel is that there are 7 atoms per 1 molecule, or in other words, 7atoms / 1molecule , or 7 atoms over 1 molecule. You multiply by seven atoms and then divide 1 molecule, as per order of operations. Simple.

For the second problem, you again did the right thing; they gave you the number of molecules, and asked you to find how many moles that is, and so you divided the number of molecules by the number of moles. Nobody cares about the units on this. But, if you want to know, the reason that it was different from the first problem is that in the first problem they gave you molecules and asked for the number of ATOMS while in the second problem, they gave you molecules and asked for the number of MOLES ; obviously, the things you divide by are going to be different when going from molecules to atoms versus molecules to moles.

I hope that that helps, it sounds like you know what you're doing. Good Luck!

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Look at Na2SO4. It has 7 atoms in one molecule. So multiply the first question by 7 for your answer
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