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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: tortoise on October 17, 2007, 07:21:50 AM

Title: Sulfur
Post by: tortoise on October 17, 2007, 07:21:50 AM

Sulfur molecules exist under various conditions as S₈, S₆,
S₄, S₂, and S.
(a) Is the mass of one mole of each of these molecules the same?
(b) Is the number of molecules in one mole of each of these molecules the same?
(c) Is the mass of sulfur in one mole of each of these molecules the same?
(d) Is the number of atoms of sulfur  in one mole of each of these molecules the same?

(a) the same, = ?
(b) not the same
(c) the same, = 32g ?
(d) not the same

I am not sure about my answers. What is the difference between (a) and (c)?

Please help me.
Thanks in advance.

Title: Re: Sulfur
Post by: Sev on October 17, 2007, 07:54:57 AM

a) no (eg. a mole of S₄ would be twice the mass of a mole of S₂)
b) yes.  Each will have Avagadro's number of molecules.
c) atomic mass will remain the same.
d) no.  eg. S₄ will contain twice the number of S₂

Title: Re: Sulfur
Post by: AWK on October 17, 2007, 08:03:53 AM

Quote

c) atomic mass will remain the same.

But question do not concern  the atomic mass

Title: Re: Sulfur
Post by: tortoise on October 17, 2007, 11:09:00 AM

What about my answer, AWK?

Title: Re: Sulfur
Post by: AWK on October 17, 2007, 11:12:53 AM

Only your answer for d is correct.
Sev gave correct answers for a and b

Title: Re: Sulfur
Post by: tortoise on October 17, 2007, 11:23:05 AM

many thanks! but, you left (c) for me to be crazy with   :'(
Can you give an answer to it?

Thanks.

Title: Re: Sulfur
Post by: AWK on October 17, 2007, 11:31:32 AM

The answer is evident - just different than yours - mass of sulfur in 1 mole of S₆ must be different than in 1 mole of S₈

Title: Re: Sulfur
Post by: gonzo on October 17, 2007, 02:31:07 PM

It might be easier for you if you remember that a mole is a specific number (Avogadro's number), so in case of c):

- is the mass of a sulfur molecule S2 the same as S4? No, the S4 is twice as big, so the mass is twice as big. So whether we have one of each molecules or 100 of each molecules we know one is twice as large mass as the other. In this case we have a mole of each molecule (a really large amount, 6.022x10^23), but it's the same amount of molecules in each group, so the bigger molecules with the bigger mass still have twice the mass in comparison to the smaller ones.

I remember being really confused about moles when I needed to use them, hopefully I haven't fed you wrong information (please someone correct me if that's the case)!