EK 1001 GCHEM #129 - Basic Question

[MCATMadness]

basic question...

for problem 129, page 11 of EK 1001 GCHEM



2SO2 + O2 --> 2SO3

how many moles of O2 are needed to produce 3.5 moles of SO3?

the answer: 3.5 * (1 mole O2/2 mole SO3) = 1.75 mol



IF the question had asked... how many O atoms are needed to produce 3.5 moles of SO3?

3.5 * (1 mole O2/2 mole SO3) * (2/1) = 3.5 O atoms

is that correct?


Basically, im confused about when you account for the subscripts (atoms) when doing basic stoich... can someone clarify?

---

Members don't see this ad.

 

[SN2ed]

Thread moved. These types of questions belong in the MCAT Study Question Q&A forum.

 

[IamSuperDoctor]

avagadros number is 6x10^23 /mol, so take that and multiply it by the number of moles O2 to get the number of O2 per 3.5 mol so3

 

[MCATMadness]

so how would the question be worded...to account for when you have to multiply by the subscript?

 

[IamSuperDoctor]

just know that avagadros number is the number of molecules per mol of a substance.

 

[MCATMadness]

check out question 99 in EK 1001 (if you can).. it says how many moles of H atoms.... so you multply by 6.

if it said how many moles of O atoms... would you multiply by 2???

 

[IamSuperDoctor]

i dont have ek :/

 

[Badger MD]

2SO2 + O2 --> 2SO3


IF the question had asked... how many O atoms are needed to produce 3.5 moles of SO3?

3.5 * (1 mole O2/2 mole SO3) * (2/1) = 3.5 O atoms

is that correct?

I believe you would do (3.5)(1 mole Oxygen/2 moles SO3) = 1.75 moles. Then you would multiply that number by Avogadro's number (6.02x10^23) to get 1.054x10^24 atoms.... Its been a while since I've done this though...

And also, when using stoich, I don't think you have to account for subscripts... Just the coefficients. I think this because whenever you need an answer in atoms, you use Avogadro's number as a conversion factor.

 

[chemtopper]

basic question...

for problem 129, page 11 of EK 1001 GCHEM



2SO2 + O2 --> 2SO3

how many moles of O2 are needed to produce 3.5 moles of SO3?

the answer: 3.5 * (1 mole O2/2 mole SO3) = 1.75 mol



IF the question had asked... how many O atoms are needed to produce 3.5 moles of SO3?

3.5 * (1 mole O2/2 mole SO3) * (2/1) = 3.5 O atoms

is that correct?


Basically, im confused about when you account for the subscripts (atoms) when doing basic stoich... can someone clarify?

yes you are right .In one mole of O2 you have two moles of O atoms .
so you need to multiply number of moles of O2 by two
Like in case of O3
you need to take this ratio
one mole of O3 = 3 moles of O atoms

 

[rls303]

yes you are right .In one mole of O2 you have two moles of O atoms .
so you need to multiply number of moles of O2 by two
Like in case of O3
you need to take this ratio
one mole of O3 = 3 moles of O atoms

So you take 1.75 moles of O2 and times that by (2mol O/1molO2) and then that by (6.022X10^23 atoms/1 mol O)...is that correct?

 

[chemtopper]

So you take 1.75 moles of O2 and times that by (2mol O/1molO2) and then that by (6.022X10^23 atoms/1 mol O)...is that correct?

yes it is correct

 

[MCATMadness]

why multiply by Na (avo number)? check out EK Gen Chem 1001 questions... 129 vs. 99

EK 129 see below for question


EK 99

Given a balanced reaction .... C2H5OH + blah blah blah --> 2H20

Using H20 moles (3 mol)...How many moles of H atoms in C2H5OH?

Here, you do not multiply by Na bc they are asking how many MOLES of H atoms, CORRECT?

Had they asked how many atoms.... then we multiply Na right? Is that correct?

 

[Rabolisk]

why multiply by Na (avo number)? check out EK Gen Chem 1001 questions... 129 vs. 99

EK 129 see below for question


EK 99

Given a balanced reaction .... C2H5OH + blah blah blah --> 2H20

Using H20 moles (3 mol)...How many moles of H atoms in C2H5OH?

Here, you do not multiply by Na bc they are asking how many MOLES of H atoms, CORRECT?

Had they asked how many atoms.... then we multiply Na right? Is that correct?

Yes, that's correct. A "mole" is just a unit for an amount of substance, and it happens to be 6 x 10^23. It's no different from a dozen being 12, or a score being 20. Thus one mole of A is 6 x 10^23 of A. A can be a molecule, an atom, an electron, a nucleus, really anything. 1 mole of O2 is 6 x 10^23 O2 molecules.