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Finding nitrogen weight in air

  • Thread starter atim
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  • #1
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Homework Statement


Air consists of approximately 78% Nitrogen in volume, 21% Oxygen and 1% Argon. The atomic weight of Nitrogen is approximately 14, that of Oxygen 16, and that of Argon 40.

Nitrogen occupies air in weight by
(1) (a) 76% (b) 77% (c)78% (d)79%

Homework Equations




The Attempt at a Solution


I don't know how to calculate, so I just tried

78*28 + 21*32 + 40 = 2896

78*28/2896 = 0.754 = 75.4%

what is the correct method?
 

Answers and Replies

  • #2
mjc123
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That is. The answer comes out very close to 75.5%, so whether you round it to 75 or 76% depends on things like the number of significant figures you took, etc. For the purpose of this question the answer is 76% (Someone has asked this question here before.)
 
  • #3
% in Vol only for gases, is a way of give the molar fraction expreseed in %.

You work is correct.
 

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