Someone please help!
Mercury has an atomic mass of 200.59 amu. Calculate the
1)mass of 3.0x10^10 atoms of mercury
2)Number of atoms in exactly one nanogram of mercury

Question

Someone please help! 
Mercury has an atomic mass of 200.59 amu. Calculate the 
1)mass of 3.0x10^10 atoms of mercury 
2)Number of atoms in exactly one nanogram of mercury

anonymous · Answer

1 ng Hg has 3 trillion atoms in it

anonymous · Answer

I know it is 10x-9 but like i have no clue how to set it up:(

aaronq · Answer

have you finished 1)?

anonymous · Answer

noooooo

aaronq · Answer

It's the same thing as if i told you, A grape weighs 1 gram, how many grams do 100 grapes weigh?

anonymous · Answer

i set it up and got 9.99617 x10-12

anonymous · Answer

like I know I set it up right... well i think i did lol. but isnt it suppose to have 2 sig figs??

aaronq · Answer

you didn't include units. And that is not the correct answer. Think about what i told you just now.

anonymous · Answer

how is it not right for part one? i used dimensional analysis???

anonymous · Answer

bc when you use sig figs it would go to 1.0 x 10^-11amu ... i thought

aaronq · Answer

What did you do?

aaronq · Answer

You're saying that 1 atom weights 200 amu, but 1 billion atoms weights much less than 200 amu.

Do you see how that doesnt make sense?

anonymous · Answer

3.0 x 10^10 atoms x (1 mol hg/6.02x10^23 atoms) x (200.59amu/1 mol hg)

aaronq · Answer

you dont have to divide by avogadro's number

anonymous · Answer

why not?

aaronq · Answer

3.0 x 10^10 atoms*200.59amu/atom

aaronq · Answer

because the mass given is not per mole, it's per atom.

anonymous · Answer

fml lol

anonymous · Answer

but i was looking online and everyone used avagadros

aaronq · Answer

wait i think you are right. People use atomic mass units interchangeably with "g/mol", which is not correct.

So, you were right, except that the units should be in grams, not amu.

anonymous · Answer

yaaaaay lol.
what about the second part?

aaronq · Answer

1 ng  = 1.0*10^-9 grams

convert that to moles (divide by atomic mass), then multiply by avogadro's number

anonymous · Answer

alright give me a second to do it out on paper.

anonymous · Answer

okay so ummmm... 3.0 x10^12 atoms....?

aaronq · Answer

yep!

anonymous · Answer

thank you chemistry god !!! lol

aaronq · Answer

lol no problem

anonymous · Answer

Can I message you with any of my other questions bc youre the bomb and a genius...!

aaronq · Answer

sure thing! tag me instead of messaging though