[uzair]

Q. Carbon .584 g reacts with 6.92g of a hypothetical element (x), if the atomic mass of Carbon is supposed to be 12 a.m.u and four atoms of that hypothetical element were used find the atomic weight of x?


Ans. Somebody solves it this way but I couldn;t understand it can somebody explain it.


(6.92/.584)*12 = 142.2  (which is the mass of four atoms of x how ??)

so, 142.2/4 = 35.5
so the atomic mass of x is 35.5 a.m.u

[Albert]

C + 4X -> CX₄

C = 12 a.m.u. = 12 g/mole
C = 0.584g => 12 g : 1 mol = 0.584 g : x mol

This means you have 0.0487 moles of carbonium. The chemical equation tells you that X needs to be four times the moles of carbonium to react with it: X = 0.1947 moles

Hence: x g: 1 mol = 6.92 g : 0.1947 mol

x = 35.5 g/mol = 35.5 a.m.u.

[Alberto_Kravina]

carbonium

Carbon, not carbonium ....other italianism...

[Albert]

...or latinism: sounds better, don't you think?

[Alberto_Kravina]

Sounds much better!  

[Borek]

In Polish - no matter whether imported from latin or italian - it will be called makaronizm (like in maccaroni)

[uzair]

C + 4X -> CX₄

C = 12 a.m.u. = 12 g/mole
C = 0.584g => 12 g : 1 mol = 0.584 g : x mol

This means you have 0.0487 moles of carbonium. The chemical equation tells you that X needs to be four times the moles of carbonium to react with it: X = 0.1947 moles

Hence: x g: 1 mol = 6.92 g : 0.1947 mol

x = 35.5 g/mol = 35.5 a.m.u.

Thanks Albert for this whatever it was Italian or Latin

the thing that is still not clear to me and i wud love to have a bit of clarification on is what does that mean (6.92/.584)*12 and as far as I thing it has to do something with "relative mass of Carbon C-12" is it  ?

[Rayan]

the equation is C + 4X --> CX₄

that is, is you write the stoichiometric ratio u'll get that
 number of moles of C /1 = number of moles of X /4
=> n (x) = 4.n (c)
=> m/Molar mass (X) = 4. m/molar mass (C)
=> molar mass of X = mass of X . molar mass (C) / 4.mass of C
=> molar mass of X = (6.92 * 12 )/4*0.584 = 35.5 g/mole
and X is Cl by the way.