Question

How many atoms of 12C are in a 3.50 g sample of this particular isotope?

Answer 1

12C: 12g 1mol
actual: 3.5g xmol
x=3.5/12=something (mol)
number of atom = something*Avogadro number

Answer 2

Well there are many ways of doing this, x=3.5/12= unknown thats stands for (mol) but really 3.5g is xmol number of it=unknown. Do you get it?

Answer 3

Kind of. So for 3.5/12= 482.4?

Answer 4

These are the options I have


2.11 x 1024 atoms



2.07 x 1024 atoms



8.01 x 1023 atoms



1.52 x 1023 atoms



1.76 x 1023 atoms

Answer 5

Would it be the first one?

Answer 6

Yes that is close enough

Answer 7

This is the answer 1.76 x 1023 atoms.

Answer 8

the last one is right. You calculate x then take the result times avogadro constant

Answer 9

Can you guys help me out with this one?

A sample of (N2H5)2C3H4O4 contains 1.084 ×1024 carbon atoms. How many moles of hydrogen atoms are in the same sample?

Answer 10

Yeah, I got that.

Answer 11

It's 10^24*

Answer 12

I know man lol

Answer 13

this is dead easy.
can you count how many H and how many C in the formula?

Answer 14

14 H and 3 C

Answer 15

good, now do some rough work
H C
14 3
x atoms 1.084 *10^24 atoms

so you can find x=1.084*10^24*14/3=blabla
number of mol of H = blabla/Avogadro constant

Answer 16

~8.4 mol I'd say

Answer 17

That's what I got but it's not in the choices I have.

These are the choices!
34.7 g



1.56 × 10-21 g



937 g



6.43 × 1020 g



31.2 g

Answer 18

those choices are in g, not in mol, I doubt that's not the right choices for this qs

Answer 19

I think they are because it's online through a school program.

Answer 20

Do I have to convert it to mol to grams now?

Answer 21

Never mind, sorry. I mixed up a question. This is the right answer.

Answer 22

lol so it's correct yeah? my brain is not really getting old lol

Answer 23

Do you mind helping me with more?

Answer 24

Haha...

Answer 25

ok, just 1 more.

Answer 26

The mass of 5.20 mol of glucose, C6H12O6 is?

A-34.7 g
B-1.56 × 10-21 g
C-937 g
D-6.43 × 1020 g
E-31.2 g

Answer 27

I get 482.2g

Answer 28

It's 482.4g. But it doesn't make sense.

Answer 29

you need to find the mass formula for glucose first. 6mols of C, 12mols H, 6mols O
MC=12
MH=1
MO=16
so 6*12+12*1+6*16=180(g/mol)
there are 5.2 mols
so mass m=180*5.2=936g

Answer 30

Oh... ok got it. I'm making harder than it is :P

Answer 31

you know it's good to remember the mass of 1 mol of some common substance. I've done these in secondary school and I still remember them now. I'd say that's big advantage.
e.g H=1, O=16, N=14, Cl=35.5, C=12... those commonly used you should remember. Save you lots of time in exam.

Answer 32

I actually do remember these basic ones. Thanks for the tip. If you have any other tips, shoot'em.

Answer 33

lol I wasn't that great at chemistry though.
remember this too
K - Na - Ca - Mg -Al - Zn - Fe- Ni - Sn - Pb - H - Cu - Hg - Ag- Pt - Au
That's extremely helpful when you deal with acid and base
And always try to make a table of information first, make the problem clearer.
And don't get scared of those Chem teachers. When they die, they'll just turn into HCON, no more no less =))

Answer 34

good luck. I'm off to bed.

Answer 35

Thanks a lot :)

Answer 36

no problem man