Determining Molecular Formula Based on Name of Molecule  [ENDORSED]

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Madeleine Farrington 1B
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Joined: Fri Apr 06, 2018 11:02 am

Determining Molecular Formula Based on Name of Molecule

Postby Madeleine Farrington 1B » Fri Apr 06, 2018 12:18 pm

Several questions in the homework list just the name of the molecule. ie question M7 in the text reads:

"Solid Boron can be extracted from solid boron oxide by reaction with magnesium metal at a high temperature. A second product is solid magnesium oxide. (a) write a balanced equation for the reaction. (b) what mass of boron can be produced when 125 kg of boron oxide is heated with 125kg magnesium?"

In questions such as these, how do you determine the molecular formula based on the name "boron oxide" in order to proceed with the problem? I had to look it up and would not have know otherwise.

Brynne Keyser 1B
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Joined: Fri Apr 06, 2018 11:03 am

Re: Determining Molecular Formula Based on Name of Molecule  [ENDORSED]

Postby Brynne Keyser 1B » Fri Apr 06, 2018 12:26 pm

You need to know the charges of the elements before you can determine the empirical formula. The charge of boron is +3 and the charge of oxygen is -2. In order for the atom to have a neutral charge, you must have two molecules of boron and 3 molecules of oxygen. This will give you the empirical formula and will allow you to later determine the molecular formula.

Hope this helps!

OrAmar-1L
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Joined: Fri Sep 29, 2017 7:04 am

Re: Determining Molecular Formula Based on Name of Molecule

Postby OrAmar-1L » Fri Apr 06, 2018 12:52 pm

I think we won't have to name the extremely complex molecules. Simple ones where you only have to add up the charges so that they are equal to zero like your question are fair game. Have a good weekend

Alexandra Wade 1L
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Re: Determining Molecular Formula Based on Name of Molecule

Postby Alexandra Wade 1L » Sat Apr 07, 2018 12:14 am

How many of these charges will we have to memorize? Are all the lower numbered elements fair game?

annie_finneran_1K
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Re: Determining Molecular Formula Based on Name of Molecule

Postby annie_finneran_1K » Sat Apr 07, 2018 5:02 pm

does it matter the order of the atoms in the formula? Like CHO vs OHC? (i know this is a bad example). and if order matters then how do we know which to put first? basically whichever is listed first?

Chem_Mod
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Re: Determining Molecular Formula Based on Name of Molecule

Postby Chem_Mod » Sun Apr 08, 2018 11:46 am

You should understand what charged ionic species you get for certain elements by looking at the periodic table. For transition metals, it is much tougher.

does it matter the order of the atoms in the formula?
Typically carbon is always there first then H, N, and O for organic molecules. For inorganic salt/molecules, the metallic element (cationic) is always put first followed by the anionic part. However, if you want to emphasize a structure of a molecule, there are cases where you would explicitly put CH2COOH but leave that for 14C and beyond.


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