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Law of Conservation of Mass??We did a lab in my science class about the law of...

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wwjd | Student, Grade 11 | (Level 1) Salutatorian

Posted February 21, 2010 at 1:17 AM via web

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Law of Conservation of Mass??

We did a lab in my science class about the law of conservation of mass. We popped uncooked popcorn with oil, measuring the mass before and after. For my lab write-up, I have to explain why it weighed less after it was popped, but I don't understand why. Help? Thanks!! :)

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pohnpei397 | College Teacher | (Level 3) Distinguished Educator

Posted February 21, 2010 at 1:21 AM (Answer #1)

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The reason that popcorn pops is because there's water inside.  When the water heats up and becomes steam, that puts pressure on the inside of the kernel.  When the pressure is put on, the kernel pops.

So why the lower weight?  Well, water is pretty heavy.  And so when the water boils off (popping the corn), the kernel has less mass than it used to.

Water makes up something like 14 percent of a kernel of popcorn.  Given that, you can see where the kernel would weigh quite a bit less with the water gone.

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lynn30k | High School Teacher | (Level 3) Associate Educator

Posted February 21, 2010 at 1:38 AM (Answer #2)

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To add to the above answer, in terms of your results showing conservation of mass:

The popcorn itself now weighs less because the water has turned to steam, and is no longer weighed along with the popcorn. The mass still exists, though; if you could weigh the escaped steam somehow, you would find where the rest of the mass is. Even though it is invisible to you, the mass is still around.

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krishna-agrawala | College Teacher | (Level 3) Valedictorian

Posted February 21, 2010 at 2:10 AM (Answer #3)

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The pop corn 'pops' or swells to much bigger size than the size of original corns used for making corn because on heating the corn the moisture inside the corn gets converted in to steam with pressure more than the normal air pressure.Due to this pressure the outer shell of the corn breaks and the stem in the corn escapes, and while escaping it also pushes out the inner material in the corn which becomes soft because of steam and heat. This steam released from the corn gets dissipated in the atmospheric air. As a result the total weight of the popcorn produced is less than the ingredients used for making popcorn. In addition to weight reduction due to loss of moisture in the corn some weight may also be lost due to evaporation of some of the oil used in making popcorn.

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