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Fundamentals J.17 (7th)

Posted: Mon Dec 03, 2018 4:26 pm
by Julia Lindner 1I
The question says to identify either a weak acid or a weak base in each compound and write the chemical equation for its reaction with water. How do you know which molecule is a weak base/weak acid just based on the formula? For example, part d has the formula NH4Br, and the answer is that NH4 is a weak acid and donates a proton to create NH3 and H3O+. Why couldn't NH4Br act as a weak base and accept a proton?

Re: Fundamentals J.17 (7th)

Posted: Mon Dec 03, 2018 5:59 pm
by Matthew Tran 1H
NH4Br is an ionic compound whose cation is ammonium NH4+ and anion is Br-. It wouldn't make sense for NH4+ to accept a proton since N has no lone pairs, so it would donate a proton to water, forming NH3 and H30+. You could also go about this particular question by recognizing that NH4+ is the conjugate acid of NH3 since these are quite common. For a-c you would have to be able to recognize that they are all ionic compounds and use the same logic.

Re: Fundamentals J.17 (7th)

Posted: Mon Dec 03, 2018 7:55 pm
by Kelsey Warren 1I
NH4 can't be a base because it can't accept a proton or donate an electron. It can't accept a proton because the N already has 4 bonds each with one H, so neither the N nor the H's can make another bond. NH4 can't donate a base because there are no lone pairs of electrons and all single bonds. Because it can't be a base, it must be an acid in this question!