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# Need help with exam question (Empirical formulae & balaned equations) watch

1. I need some help with this exam question, I've calculated the empirical formula but have a feeling it might be wrong so I can't do the second part of the q.

Water, ammonia, and sulfur dioxide react together to form a compound A which has the following % composition by mass:

N, 24.12%
H 6.94%
S, 27.61%
O, 41.33%

Calculate the empirical formula of compound A
[I got N2H4SO3]

Suggest a balanced equation for the formation of compound A from the reaction of water, ammonia and sulfur dioxide.

Thanks!
2. (Original post by vaishalir)
I need some help with this exam question, I've calculated the empirical formula but have a feeling it might be wrong so I can't do the second part of the q.

Water, ammonia, and sulfur dioxide react together to form a compound A which has the following % composition by mass:

N, 24.12%
H 6.94%
S, 27.61%
O, 41.33%

Calculate the empirical formula of compound A
[I got N2H4SO3]

Suggest a balanced equation for the formation of compound A from the reaction of water, ammonia and sulfur dioxide.

Thanks!
I imagine that it should be 6H as the answer is ammonium sulfite

EDIT: Golly did I write 6? I meant to write 8 for (NH4)2
3. I got n2h8so3

and the equation would therefore be:
h2o + 2nh3 + so2 ----> n2h8so3.

also btw ammonium sulfite is (NH4)2SO3 so this appears to be correct but i ofc might have made a mistake.
4. (Original post by charco)
I imagine that it should be 6H as the answer is ammonium sulfite
But from calculating the empircial formula, how would it be possible to get 6H?

(Original post by hoafanuk)
I got n2h8so3

and the equation would therefore be:
h2o + 2nh3 + so2 ----> n2h8so3.

also btw ammonium sulfite is (NH4)2SO3 so this appears to be correct but i ofc might have made a mistake.
I see where you got H8 from , but if Hydrogen exists as H2 because its a diatomic molecule don't i use the RAM of it as 2 and not 1? or do i just use 1
5. (Original post by vaishalir)
But from calculating the empircial formula, how would it be possible to get 6H?

I see where you got H8 from , but if Hydrogen exists as H2 because its a diatomic molecule don't i use the RAM of it as 2 and not 1? or do i just use 1
If the question says x% is made up of H2 then you would do x/2 but as the question just says H you divide by 1.
6. (Original post by hoafanuk)
If the question says x% is made up of H2 then you would do x/2 but as the question just says H you divide by 1.
Cool, alright, thank you!
7. (Original post by vaishalir)
Cool, alright, thank you!
No problem!
8. (Original post by vaishalir)
I need some help with this exam question, I've calculated the empirical formula but have a feeling it might be wrong so I can't do the second part of the q.

Water, ammonia, and sulfur dioxide react together to form a compound A which has the following % composition by mass:

N, 24.12%
H 6.94%
S, 27.61%
O, 41.33%

Calculate the empirical formula of compound A
[I got N2H4SO3]

Suggest a balanced equation for the formation of compound A from the reaction of water, ammonia and sulfur dioxide.

Thanks!
Empirical formula is always
(%) mass
/ Ar (relative atomic mass, in periodic table) for each individual thing
/ the smallest number there
(multiplied by anything so they're all just about whole numbers)
Ratio
Then you say "Empirical formula is e.g. C2H6"
Then if it says to work out the molecular formula, you divide the molecular mass with the empirical mass, then multiply the empirical formula with the answer.
So if it said Mr = 60, you divide it by 30 (C2H6) = 2
C2H6 x 2 = C4H10

Maybe not (always) for AS, but you must be clear and say "Empirical formula is this" and "Molecular formula is this", to leave nothing to ambiguity.

So tl;dr
(%) mass
/Ar
make ratio

empirical formula is...
Mr / mass of empirical formula = X
empirical formula x X = molecular formula

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