mole concept(ICSE -2006)

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GIVEN THAT HE MOLECULAR MASS OF THE COPPER OXIDE IS 80, WHAT VOLUME OF AMMONIA
(measured at STP) IS REQUIRED TIO COMPLETLY REDUCE 120 g OF CuO?

EQUATION= 3CuO+2NH3 = 3Cu +3(WATER) +N2
Volume occupied by 1 mole of gas at STP =22.4 litres

PLEASE SOLVE THIS
I KNOW THE ANSWER BUT DONT KNOW THE CONCEPT BEHIND IT

ANSWER=22.4 dm3

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3CuO+2NH3=3Cu+3H2O+N2
MOLECULAR MASS OF CUO=80
MOLECULAR MASS OF 3 CUO =3*80=240g
MOECULAR MASS OF NH3=17g
MOLECULAR MASS OF 2 NHE=2*17=34g
240g of cuo is reduced by 34g of NH3
SO 120G OF CUO IS REDUCED BY (34*120)/240=17g of NH3

THER4 17g OF NH3 OCCOPIES 22.4dm3
so 17g OF NH3 OCCUPIES (22.4*17)/17=22.4dm3
by the way dm3 & litre r the same

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thanks a lot !

Subject: Re: mole concept(ICSE -2006) Sun Feb 24, 2008 8:44 pm

the molecular mass of amonia is not given in the question, how did you get it?

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molecular wt of nitrogen=14
molecular wt of hydrogen =3*1=3
14+3=17
there4 of 2NH3=2*17
=34g

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SINCE THE MOLECULAR MASS IS NOT GIVEN IN THE QUESTION
CAN WE SOLVE LIKE THIS ( I MEAN WHETHER THE METHOD IS CORRECT)

3CuO+2NH3=3Cu+3H2O+N2
MOLECULAR MASS OF CUO=80
MOLECULAR MASS OF 3 CUO =3*80=240g
1 mole 0f NH3 at STP =22.4dm3(given)
since in the equation the volume of NH3 is double
there4 volume of NH3= 44.8dm3
240g of cuo is reduced by 44.8dm3of NH3
SO 120G OF CUO IS REDUCED BY (44.8*120)/240=22.4dm3 of NH3

this way we can directly get the answer without finding the molecular
mass of NH3
and I suppose thats the reason that no molecular mass of N,O or
NH3 is given becoz we dont require it !

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i m not sure............but i dont think dat the method is correct.i feel.........it is always better to find the molecular mass in such type of sums!!!!!!!!!!

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Since in the question the molecular mass of H,N or NH3 is not given
then we have to learn the molecular mass of elements ?
I mean there so many of them and we dont know which compounds
may ICSE give.

and far as I know molecular mass of elements are given in the
question if required.

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dat's crazy i'll die lern'in all da mol.masses. i'm just learn'in da imp.1's like O2,N,H,Cl,etc. not those rare 1's

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just learn the imp 1s.molecular mass of elements r given in the questions if required.don't worry!
ALL THE BEST 4 UR EXAMS!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

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good problem