Identifying lewis acids and bases

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Aaina 2D
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Identifying lewis acids and bases

Postby Aaina 2D » Mon Nov 16, 2020 11:37 am

Hi! I came across a problem where it asked me to identify which reactant is a lewis acid and which reactant is a lewis base.

CH3NH2 + CH3Br → Br- + (CH3)2NH2+

From this equation, how do we know which reactant is a lewis acid/base?

Emmeline Phu 1G
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Re: Identifying lewis acids and bases

Postby Emmeline Phu 1G » Mon Nov 16, 2020 11:48 am

Hi! Lewis acids accept a pair of electrons to form a covalent bond whereas Lewis bases donates a pair of electrons to form a covalent bond. So in other words, Lewis acids are electron acceptors and Lewis bases are electron donors. To figure out which molecule is which, look at whether or not the molecule is gaining electrons or losing electrons. In this case, CH3NH2 gained a proton on the product side of the reaction((CH3)2NH2+); therefore, it is losing electrons; whereas CH3Br gained an electron from losing CH3 (Br- on the product side). Therefore, CH3NH2 is a Lewis base and CH3Br is a Lewis acid. Hope this helps! :)

Anna Yakura 2F
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Re: Identifying lewis acids and bases

Postby Anna Yakura 2F » Mon Nov 16, 2020 12:00 pm

Hello, here's the process I use when trying to figure these out:
1.) Identify any cations or anions. Cations will be Lewis acid because they can accept and electron, while anions will be Lewis bases because they have an electron to give.
2.) For anything that's neutral, look for any electron deficient atoms (like Boron, or radicals) that can accept an electron. These will be Lewis acids. Then look for anything that has lone pairs (that they can donate). These are Lewis bases!

Ria Nawathe 1C
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Re: Identifying lewis acids and bases

Postby Ria Nawathe 1C » Mon Nov 16, 2020 1:05 pm

Cations, molecules with electron deficient central atoms (like BF3), and molecules with polar double bonds (like CO2) tend to be lewis acids since they are more likely to accept an electron pair. Anions and molecules with lone pairs (like H2O) tend to be lewis bases since they have electrons to donate. Hope this helps!

Samuel Flores 1E
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Re: Identifying lewis acids and bases

Postby Samuel Flores 1E » Mon Nov 16, 2020 1:51 pm

Hello! As said above, Lewis acids are electron accepters, while Lewis bases are electron donors. One thing I'll add is that we see that the Br becomes an anion once it's a product. This will help us indicate that it gained electrons, so the Br in the CH3Br will accept electrons in the process of this chemical reaction. Therefore, CH3Br is a Lewis Acid.

Hope this helps!

Yun Su Choi 3G
Posts: 92
Joined: Wed Sep 30, 2020 10:09 pm

Re: Identifying lewis acids and bases

Postby Yun Su Choi 3G » Mon Nov 16, 2020 8:37 pm

Will we always be given a chemical equation like the one above?


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