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Finding a stoichiometric coefficient

  • Thread starter rustynail
  • Start date
  • #1
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Hello, I am currently taking a college level chemistry class. I am struggling with this problem, any help would be greatly appreciated.

Homework Statement


We have a certain quantity of

[tex] CuSO_{4} \cdot \gamma H_{2}O [/tex]

If our sample is formed of (25,5% Cu), (12% S), (57,7% O) and (4.04% H), what is the value of gamma ?


Homework Equations


None given.


The Attempt at a Solution


I have determined the mass of 1mol of each element, the mass of 1mol of CuSO_4 (111.611g) and really, I'm stuck there.

Please don't spoil the fun for me, just give me some hints.

(edit) : I have done this much more :

Mass of 1mol Cu = 63.546g

(63.546g/111.611g)*100 = 56.94% Cu in CuSO_4

56.94%/25.5% = 2.2328 (increment factor)

So the mass of the hydrated CuSO_4 should be

111.611g * 2,2328= 249.21g

249.21g - 111.611g = 137.6g H2O

and 137.6g/18(g/mol)= 7.6 mol H2O

but it does not give me an integer...
 
Last edited:

Answers and Replies

  • #2
AGNuke
Gold Member
455
9
Try some Approximations in calculations. For example, Molar Mass of Cu is good as 63.5.
 
  • #3
53
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thanks AGNuke, you mean that some approximations could get me closer to an integer coefficient? Do you think my attempt at a solution made sense?
 
Last edited:
  • #4
AGNuke
Gold Member
455
9
No. You can apply the percentage "after" you had taken the molar mass of all the compound (including the hydration) part in consideration.
Take molar mass of compound as M[CuSO4]+γ[M(H2O)]

Also, you took the molar mass of CuSO4 incorrect.

And don't panic if you don't get answer in integer. Just try rounding them up or down.
 

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