Mass Percent Composition

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annikaying
Posts: 94
Joined: Sat Sep 14, 2019 12:16 am

Mass Percent Composition

Postby annikaying » Tue Oct 01, 2019 12:17 pm

Is it necessary to imagine that you have 100g of a molecule when trying to figure out the empirical and molecular formulas? You are trying to convert everything to moles, so if you are originally given grams of the different chemicals in the molecule, could you not skip the conversion to mass percent composition and just go straight to moles?

Jamie Lee 1F
Posts: 106
Joined: Fri Aug 09, 2019 12:16 am

Re: Mass Percent Composition

Postby Jamie Lee 1F » Tue Oct 01, 2019 12:29 pm

For the 100% aspect of your question, I'm not sure if we'd get problems where the percentages don't add up to a hundred. If they didn't, you would have to divide and find out the masses yourself.

If you were given a sample of x grams and the question told you that the sample was analyzed and had certain amounts of whatever substances, and you didn't use mass percent composition and immediately converted those grams of given substances to moles, I believe you would just have parts but no definite whole. Since empirical and molecular formulas are inherently part to whole ratios, you wouldn't end up with the accurate answer.

Ashley Kim 3F
Posts: 50
Joined: Thu Jul 25, 2019 12:17 am

Re: Mass Percent Composition

Postby Ashley Kim 3F » Tue Oct 01, 2019 12:44 pm

I think that imagining that you have 100g of a molecule when figuring out empirical and molecular formulas is just a useful tip for when the numbers are not particularly pretty or easy to work with, but not a necessary component. However, you can not go directly to moles from the given grams of different atoms in a molecule because you need to find the mass of the individual atoms to figure out how many moles of that particular atom are in the molecule.

Ashley Nguyen 2L
Posts: 103
Joined: Sat Aug 17, 2019 12:18 am
Been upvoted: 1 time

Re: Mass Percent Composition

Postby Ashley Nguyen 2L » Tue Oct 01, 2019 12:47 pm

I believe that it is not necessary to imagine you have 100g of a molecule if you are already given the specific grams. However, it makes it much easier to work with the numbers when you are using 100g of a sample and it's a basic step you can take at the beginning of any mass percent composition problem.

Norman Dis4C
Posts: 101
Joined: Sat Sep 28, 2019 12:16 am

Re: Mass Percent Composition

Postby Norman Dis4C » Tue Oct 01, 2019 1:57 pm

You only have to imagine there is 100 grams when %composistion is given but not the mass. (the number of grams you used is not fixed, you can use whatever you want as long as you keep the calculation simple and clear, but usually, 100 grams is the most straightforward and simple)

BeylemZ-1B
Posts: 95
Joined: Thu Jul 25, 2019 12:17 am

Re: Mass Percent Composition

Postby BeylemZ-1B » Wed Oct 02, 2019 3:20 pm

Norman Dis4C wrote:You only have to imagine there is 100 grams when %composistion is given but not the mass. (the number of grams you used is not fixed, you can use whatever you want as long as you keep the calculation simple and clear, but usually, 100 grams is the most straightforward and simple)


I definitely agree! You definitely do not HAVE to use 100 grams, but it is the most straightforward and simple way to go about solving the problem.


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