Audio Visual Focus Topic Empirical and Molecular Formulas Pre-Assessment

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Jasmine Reddy DIS 1E
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Joined: Fri Sep 28, 2018 12:17 am

Audio Visual Focus Topic Empirical and Molecular Formulas Pre-Assessment

Postby Jasmine Reddy DIS 1E » Tue Oct 02, 2018 1:14 pm

Question 14 on the Empirical and Molecular Formulas pre-test states, "If vitamin C is 40.9% C, 4.58% H, and 54.5% O what is its empirical formula?"
Are these percentages referring to mass percentage of each element within vitamin C?

Kelly Hollman
Posts: 33
Joined: Fri Sep 28, 2018 12:27 am

Re: Audio Visual Focus Topic Empirical and Molecular Formulas Pre-Assessment

Postby Kelly Hollman » Tue Oct 02, 2018 1:17 pm

Yes, exactly. Each percentage is for each individual element of the vitamin.

Cody Do 2F
Posts: 62
Joined: Fri Sep 28, 2018 12:23 am

Re: Audio Visual Focus Topic Empirical and Molecular Formulas Pre-Assessment

Postby Cody Do 2F » Tue Oct 02, 2018 8:37 pm

Yep! Since you have the mass percentage breakdown now, use that information to find the empirical formula. You do this by pretending that we have 100g of the substance (this makes it easier on us as the percentages can now just be used as grams). Divide each element by its molecular weight, which is found on the periodic table (C is 12.011, H is 1.01, O is 16.00). Then from the three values you end up with, divide all of them by the SMALLEST of the three. You should get a ratio with a fraction now—but empirical formulas can't have fractions/decimals, so you have to multiply the ratio until you reach the smallest possible whole number ratio!


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