Hii, I have a few qns here.
Miscellanous qn: Do we still need to know what’s a mass
spectrometer, NMR spectrum for H2 Chem?
Stoichiometry: A giant molecule contains a large amount of
carbon, mainly of isotopes 12C and 13C. It was found that the
relative atomic mass of carbon in the molecule is 12.20. What is
the ratio of 12C to 13C ?
Ans: 4:1
It happens that this is a MCQ qn. So the approach
is just (12×0.
+
(13×0.2) = 12.2
I was wondering, what if this is not a MCQ qn? I know
we can let them be x and y.
So it becomes 12x + 13y = 12.2 . However there is only one eqn.
Gasesous State: Under extereme conditions, gallium chloride
Ga2Cl6 can also be formed via the endothermic dimerisation of
GaCl3. The two species can exist in dynamic equilibrium under
suitable conditions.
2GaCl3(g) two way arrow Ga2Cl6(g)
(1) In an experiment, a total pressure of 7.75×10-3 N
m-2 was measured when a 0.661g sample of GaCl3 was allowed to
dimerise in a 1.80dm3 vessel at 200 degrees.
Calculate x, the fraction of GaCl3 that dimerised at 200
degrees, assuming ideal gas behaviour.
I apply pV=nRT, where turns n is 0.00354904
Initial mass is 0.661g of GaCl3, n = 0.00375141
Fraction that dimerised, x = (0.00375141 – 0.00354904) /
0.00375141 = 0.053945
But the answer is 0.108! (No working provided)
Thanks for answering!!!
For the 1st qn, let X be the % of C12. Then
(X/100)(12)+((100-X)/100)(13) = 12.2 and solve for X.
For the 2nd qn, the number of moles when using PV=nRT is the
total number of moles of both gaseous species (ie. both the monomer
and the dimer).
2GaCl3 <---> Ga2Cl6
Initial : 0.00375141 and 0
Change : -2X and +X
Equilibrium : (0.00375141 - 2X) and X
Total moles of gaseous species = (0.00375141 - 2X) + X
= 0.00354904 (from PV=nRT)
Solve for X.
