Calculate 1.The amount 2.The mass
3.The number of molecules
4.Number of atoms that contains 11.5dm³ of ammonia (NH3)gas at s.t.p.
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Clara M. asked • 05/16/18
At STP, what is the mass of 11.2 liters of O2 gas?
I tried solving this myself and got 16.0 g, but wasn't quiet to sure if I did the problem right.
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J.R. S. answered • 05/16/18
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Ph.D. in Biochemistry--University Professor--Chemistry Tutor
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While the previous apprach could have been used, when the system is at STP, you dont have to use PV = nRT. All you need to know is at STP 1 mole of an ideal gas = 22.4 liters. Thus, 11.2 L x 1 mol/22.4 L = 0.5 moles
0.5 moles x 32 g/mole = 16 g.
You were correct.
The previous answer has several errors. First , n = 0.499 =0.5 mokes, not 0.0446. Second error is that molar mass of O2 is 32 g, not 16 g.
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Sarrita A. answered • 05/16/18
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University of Cambridge Graduate with PhD in Biochemistry
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You need the equation: PV=nRT
P=1atm
T=273K
V=11.2L
R=0.0821
n=?
rearrange the equation in terms of n:
PV=nRT - divide both sides by RT
n=PV/RT
now put in the info:
1x 11.2/ 273x0.0821
11.2/22.4133
=0.0446 moles of O2
now find the mass by:
0.0446 moles x atomic mass of O2
=0.0446 x 15.99(2)= 1.426g (3 sig fig)
you have 1.426g of O2