Finding the mass of a molecule


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allyssa bradley 1H
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Joined: Wed Sep 30, 2020 9:47 pm

Finding the mass of a molecule

Postby allyssa bradley 1H » Tue Oct 27, 2020 12:41 pm

Hi guys, I came up with a question after working on problem 17 of the Sapling homework this week. I was a little confused about finding the mass of a diatomic hydrogen molecule -- presumably, this is about 2.014 amu, or 2 protons and 2 electrons, but our equation sheet doesn't offer a conversion quantity for amu to grams, which makes me feel like I am going about this problem the wrong way. Is there a better alternative to find the mass besides using the amu to grams conversion?

Hannah Lechtzin 1K
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Joined: Wed Sep 30, 2020 9:31 pm

Re: Finding the mass of a molecule

Postby Hannah Lechtzin 1K » Tue Oct 27, 2020 2:31 pm

To find the mass of diatomic hydrogen you multiply the molar mass of hydrogen by 2 because diatomic just means two, so you're finding the mass of H2. From there you can covert the moles to grams, kg, or whatever unit you might need. I hope this helps!

Hasmik Dis 2F
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Joined: Wed Sep 30, 2020 9:50 pm

Re: Finding the mass of a molecule

Postby Hasmik Dis 2F » Sat Oct 31, 2020 1:05 am

I think your confusion is in the "amu" which just means "atomic mass units." That number just means mass also, so whenever you see "2.014 amu" it is essentially 2.014 grams. There's no actual conversion from amu to grams.

Arezo Ahmadi 3J
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Re: Finding the mass of a molecule

Postby Arezo Ahmadi 3J » Sat Oct 31, 2020 9:44 pm

When you are using 2.014 amu, this essentially means grams per mole, so you would have to convert to grams by dividing by Avogadro's Number. Then, always make sure you check the context of the question because when using equations such as DeBroglie Equation, the mass needs to be in kilograms, so divide by 1000. You can use dimensional analysis when converting from grams per mole to the units you need so that it can become clear, and you would only need the equation sheet to use Avogadro's Number to convert to grams.

Here is what dimensional analysis would look like:

(2.014 g H2)/(1 mol H2) * (1 mol H2/ 2 mol H) * (1 mol H /(6.022 x 10^23)

You would get a value in grams because the other units cancel out.

Hope this helps!

Brianna Chen 3F
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Joined: Wed Sep 30, 2020 10:11 pm

Re: Finding the mass of a molecule

Postby Brianna Chen 3F » Sat Oct 31, 2020 11:34 pm

Anytime you see the word "diatomic," you would find the molar mass of two molecules. In this case, it is two Hydrogen molecules (H2). Then, you can use this value in your conversion!

Andre Fabian 1F
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Re: Finding the mass of a molecule

Postby Andre Fabian 1F » Sat Oct 31, 2020 11:36 pm

To find the mass of a single molecule, you would divide its molar mass by Avagadro's constant (6.022 x 10^23).

In addition, the masses found underneath each element in the periodic table are in amu, but we use them to calculate the molar mass of a certain molecule, in which we divide the grams used of a substance in a reaction by, in order to find the number of moles of the constituent substance.



Hope this helps!
Andre

Nan_Guan_1L
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Joined: Wed Sep 30, 2020 9:59 pm

Re: Finding the mass of a molecule

Postby Nan_Guan_1L » Sun Nov 01, 2020 5:50 pm

by diatomic structure, this question is referring to H2. so in order to find the mass of one H2 molecule, you just take the molar mass of H2, which is 2.014, and divide that by Na (Avagadro's constant), because this constant is referring to the number of molecules in one mole of substance. divide the molar mass by Na, and you get the mass of one molecule. hope that helps! :)


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