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Angela Prince 1J
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Joined: Sat Aug 24, 2019 12:17 am


Postby Angela Prince 1J » Fri Nov 08, 2019 3:11 pm

Can someone explain the first question about finding the empirical formula of that compound that was on the midterm?

Annie Chantasirivisal_4G
Posts: 114
Joined: Wed Sep 18, 2019 12:21 am

Re: Midterm

Postby Annie Chantasirivisal_4G » Fri Nov 08, 2019 5:36 pm

It's difficult to explain because I don't remember the question word for word, but I found it really similar to the first question on the practice exam Dino Nuggets that UA Lyndon made where you're given molecules and you try to find mass percentage composition from there. I think it'd be helpful to look up that question, because there have been a couple of questions about it and also replies explaining how to solve that problem; you would then adjust it to fit the problem asked in the midterm.

If I remember correctly, in the midterm I think you would find the grams of H from H2O, C from C2O, and N from N2, and then subtract those grams from the total of the compound in the question for the total amount of O in grams, convert everything to moles, and then obtain the empirical formula through there.

Reagan Smith 1H
Posts: 50
Joined: Sat Jul 20, 2019 12:16 am

Re: Midterm

Postby Reagan Smith 1H » Fri Nov 08, 2019 5:47 pm

Since you were provided the mass of the compound, I think it was riboflavin, and you had the mass of each of the products, H2O, CO2, and N2, plus you had the balanced chemical equation , you could solve for the number of moles of C in CO2 using a conversion factor of 1 mol C per one mol CO2, the number of moles of H in H2O using a conversion factor of 2 mols H per 1 mol H2O, and the moles of N in N2 using a conversion factor of 2 mol N per 1 mol N2. Then you would convert those to grams, subtract those from the total amount of riboflavin given to find the grams of O. Then you would convert all of those back to moles, divide by the smallest and make sure you have whole numbers.

Posts: 52
Joined: Wed Sep 11, 2019 12:16 am

Re: Midterm

Postby TYun_1C » Fri Nov 08, 2019 6:09 pm

I think the key of the question is that after you have to remember that the hydrocarbon you are solving for has oxygen. In other words, after solving for the moles of all other elements, you must convert these into grams, add the grams up, and subtract from the total grams to find the grams of oxygen. From there you can solve for miles of oxygen and finish the calculations.

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