If a balloon, with its rubber weighing 2g, has 4g of butane/C4H10 added into it, how much does the balloon weigh after adding the butane?
**The answer is NOT 6g, according to this video: http://www.youtube.com/watch?v=cgGghuA2r…
and tell me how/why you got the answer.
**The answer is NOT 6g, according to this video: http://www.youtube.com/watch?v=cgGghuA2r…
and tell me how/why you got the answer.
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The MASS of the butane and balloon will certainly be 2g + 4g = 6g.
The question "how much does it weigh?" is not the same as mass, supposing the weight is determined by putting the balloon on a scale.
In the latter case you have to allow for the balloon's buoyancy in air. Supposing the balloon to be not very elastic so the pressure inside the balloon is essentially 1 atmosphere, and that the experiment was conducted at 25°C:
(4 g C4H10) / (58.12259 g C4H10/mol) = 0.07 mole butane
0.07 mole of butane would displace 0.07 mole of air. Since the molar mass of dry air is approximately 28.97 g/mol, the balloon displaces:
(0.07 mol) x (28.97 g/mol) = 2 g of air
So the net weight of the balloon would be 6g - 2g = 4g as measured on a scale.
(I emphasize this is NOT the mass of the balloon.)
If the balloon could be weighed in a vacuum, it would weigh 6 grams.
The question "how much does it weigh?" is not the same as mass, supposing the weight is determined by putting the balloon on a scale.
In the latter case you have to allow for the balloon's buoyancy in air. Supposing the balloon to be not very elastic so the pressure inside the balloon is essentially 1 atmosphere, and that the experiment was conducted at 25°C:
(4 g C4H10) / (58.12259 g C4H10/mol) = 0.07 mole butane
0.07 mole of butane would displace 0.07 mole of air. Since the molar mass of dry air is approximately 28.97 g/mol, the balloon displaces:
(0.07 mol) x (28.97 g/mol) = 2 g of air
So the net weight of the balloon would be 6g - 2g = 4g as measured on a scale.
(I emphasize this is NOT the mass of the balloon.)
If the balloon could be weighed in a vacuum, it would weigh 6 grams.