Homework Question F.9

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Kimberly Bauer 4E
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Joined: Thu Jul 25, 2019 12:17 am

Homework Question F.9

Postby Kimberly Bauer 4E » Thu Oct 03, 2019 11:12 pm

Vanillin is found in vanilla extracted from Mexican orchids.A report on the analysis of vanillin listed the mass percentage com- position as 63.15% C, 5.30% H, and 31.55% O. In what atom ratios are the atoms present in vanillin?

For this problem, I understand we're finding the empirical formula. All of the percentages add up to 100 so to do the rest of the problem and convert it to moles would I do, for example, 63.15/100 to convert to moles?

Siddiq 1E
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Re: Homework Question F.9

Postby Siddiq 1E » Thu Oct 03, 2019 11:14 pm

Yes exactly. For these questions assume you have 100g of compound for simplicity's sake, and convert to moles from there.

Amanda Lin 2I
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Re: Homework Question F.9

Postby Amanda Lin 2I » Thu Oct 03, 2019 11:16 pm

Yes, you would use a 100 g sample, so there would be 63.15 g C, 5.30 g H, and 31.55 g O. You would then convert these to moles.

Hussain Chharawalla 1G
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Re: Homework Question F.9

Postby Hussain Chharawalla 1G » Thu Oct 03, 2019 11:19 pm

Yes, you are looking for the empirical formula because of the key word "ratio" of atoms. And just to clarify, converting between percentages to moles does NOT mean divide by a hundred. It means we are taking a hypothetical sample of 100 grams and taking respective percentages of that.

Once you divide by molar mass, divide by lowest mole number to find a ratio.

Anne Tsai 1F
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Re: Homework Question F.9

Postby Anne Tsai 1F » Thu Oct 03, 2019 11:19 pm

Yes, you would assume that your sample is 100 g, but to convert to moles, you actually have to divide by the molar mass of each element as found on the periodic table (so 12.01 g/mol for C). You don't need to divide 63.15 by 100 because if you assume the sample is 100 g, then 63.15% of 100 would just be 63.15.

Kimberly Bauer 4E
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Joined: Thu Jul 25, 2019 12:17 am

Re: Homework Question F.9

Postby Kimberly Bauer 4E » Fri Oct 04, 2019 12:50 am

Anne Tsai 1F wrote:Yes, you would assume that your sample is 100 g, but to convert to moles, you actually have to divide by the molar mass of each element as found on the periodic table (so 12.01 g/mol for C). You don't need to divide 63.15 by 100 because if you assume the sample is 100 g, then 63.15% of 100 would just be 63.15.


So you would put 63.15/12.01?

J Medina 2I
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Joined: Wed Sep 25, 2019 12:17 am

Re: Homework Question F.9

Postby J Medina 2I » Fri Oct 04, 2019 1:00 am

Kimberly Bauer 4E wrote:
Anne Tsai 1F wrote:Yes, you would assume that your sample is 100 g, but to convert to moles, you actually have to divide by the molar mass of each element as found on the periodic table (so 12.01 g/mol for C). You don't need to divide 63.15 by 100 because if you assume the sample is 100 g, then 63.15% of 100 would just be 63.15.


So you would put 63.15/12.01?


Yes and that would give you the number of moles of C and then you would find this value for O and H by dividing by their respective molar masses to get their number of moles in Vanillin. Then you would divide each of these values by the one with the lowest amount of moles to get the ratios of moles. The question is asking for mole ratios, which is the Empirical formula so you'd have to multiply the values you get by a number that will make them all whole numbers.


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