Question

What is the mass, in grams, of a sample of 7.83 × 1024 atoms of helium (He)? Show your work or explain the steps that you used to determine your answer.

Answer 1

Convert the # of atoms of He to # of moles of He. Then, multiply # of moles by the molar mass of He found on the periodic table.

Answer 2

How do i convert the number of atoms into the number of moles?

Answer 3

Great question. That is the part where most people get stuck. Remember Avogadro's Number.
N = 6.022 * 10^23 particles/mol; particles can mean atoms, molecules, etc. But for right now, we're dealing with atoms.

Answer 4

Do you see a way to take your atoms and Avogardo's Number and get moles? Hint: look at the units.

Answer 5

yeah kind of i just dont get where we got the 6.022 from. like is that a set number we are always suppose to use?

Answer 6

I'm not sure either. People in a lab did a buncha experiments and calculations to give us this constant. Keyword: Constant. It never changes. It'll be an interesting project to figure out where it comes from though.

Answer 7

okay so to convert the number of atoms into the number of moles i just use the same formula or equation

Answer 8

Basically. Did you find how many moles of He we have yet?

Answer 9

yeah would it be 13.0

Answer 10

if it was rounded

Answer 11

Err, I guess that seems right lol. I dont have a calculator with me. You divided the mass by N right? And you shouldn't round yet.

Answer 12

the atomic mass of helium

Answer 13

So, we have 13.X mols of He. On a regular periodic table, under Helium, you can find the molar mass of He, which has the units g/mol.

Answer 14

Whoops, I meant the # of atoms divided by N. x_x

Answer 15

oh okay
yeah i got 13.00232481 for the number of moles

Answer 16

Good. Now, look at my 2nd recent post lol. Molar mass of He is in g/mol. Do you see how we can get the grams of 13 mol He?

Answer 17

okay yeah i did i got 52.04310528
so would i round it now or do i keep that decimal as my answer

Answer 18

Good job, yeah I suppose you should round it to the nearest tenth or hundredth, whatever the question may ask.

Answer 19

okay thank you so much!