Midterm Solutions Fall 2018-2019 year

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Daniel Kim 1D
Posts: 38
Joined: Wed Oct 03, 2018 12:17 am

Midterm Solutions Fall 2018-2019 year

Postby Daniel Kim 1D » Sat Dec 08, 2018 1:25 pm

For question #2, the solution manual utilizes 2.0158 g for H when that is actually the weight in grams for two Hydrogen atoms. In order to solve this problem, which one will I have to use? 1.007 g H or 2.0158 g H2? I can follow along the other steps but I can’t seem to understand how to find the moles of Hydrogen.

Chloe Thorpe 1J
Posts: 77
Joined: Fri Sep 28, 2018 12:16 am

Re: Midterm Solutions Fall 2018-2019 year

Postby Chloe Thorpe 1J » Sat Dec 08, 2018 2:16 pm

You can use either one, but you have to tweak your calculation slightly to account for how many mol of H there are in H2O.

Using Molar Mass of H2:

0.3172 g H2O * (1 mol H2O/18.015 g H2O) * (2.0158 g H2/1 mol H2O) = 0.03552 g H

Using Molar Mass of H (personally, I use this method):

0.3172 g H2O * (1 mol H2O/18.015 g H2O) * (2 mol H/1 mol H2O) * (1.008 g H/1 mol H) = 0.03552 g H

yaosamantha4F
Posts: 31
Joined: Fri Sep 28, 2018 12:29 am

Re: Midterm Solutions Fall 2018-2019 year

Postby yaosamantha4F » Sat Dec 08, 2018 2:17 pm

Is this the problem about the empirical/molecular formulas of gallic acid? After calculating the number of g of H produced through combustion using the molar mass of H2O and the molar ratio of H and H2O, you divide by H's molar mass (1.007) to find the number of moles!


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