Homework 12.9  [ENDORSED]

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Miya McLaughlin 2B
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Homework 12.9

Postby Miya McLaughlin 2B » Wed Nov 16, 2016 3:42 pm

For this problem, it asks if a set of equations can be classified as reactions between Bronsted acids and bases. I know that means a proton must be transferred from one molecule to another. However, with the reactions they gave us, I don't know how to tell if a proton is transferred in that way? The solutions manual didn't explain why, it merely stated if a proton was or wasn't transferred.

Does anyone know how to tell when a proton is transferred from an acid to a base, for reactions with more complicated molecules?

E.g. NH4I(s) --> NH3(g) + HI(g)

Chem_Mod
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Re: Homework 12.9  [ENDORSED]

Postby Chem_Mod » Sat Nov 19, 2016 2:43 pm

Using your example it should be clear when a proton is transferred:

NH4+I-(s) ---> NH3(g) + HI(g)

Ammonium iodide is a salt and the proton was transferred from the ammonium cation (NH4+) to the iodide anion (I-) to form NH3(g) and HI(g).

Pauline Tze 3B
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Re: Homework 12.9

Postby Pauline Tze 3B » Sun Nov 20, 2016 2:19 am

Can someone explain how they wrote out the complete ionic equation for this part of the question?
d. NH4I + KNH2 --> KI + 2NH3

I understand the breakdowns of:
NH4I --> NH4+ and I-
KNH[sub]2
--> K+ NH2
KI --> K+ + I-

But I don't understand why 2NH3 would break down into 2NH2- + 2H+. Doesn't the geometry indicate that it should be ammonia with 3 bonds (and not an amide ion with hydrogen ion)? And even if this was the case, wouldn't it be canceled out by the NH2- on the left side of the equation?

Thank you in advance.

Crystal_Chung_1A
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Re: Homework 12.9

Postby Crystal_Chung_1A » Mon Nov 21, 2016 9:14 am

I tried looking the 2NH2- + 2H+ dissociation up on Google, and I got information on ammine dissociation, will that be something we are expected to know? I am also confused over how to know 2NH3 dissociates into 2NH2- + 2H+. Thanks in advance

Belicia Tang 1B
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Re: Homework 12.9

Postby Belicia Tang 1B » Mon Nov 21, 2016 8:26 pm

@Pauline Tze

Here's the ionic equation:

NH4(+) + I(-) + K(+) + NH2(-) --> K(+) + I(-) + 2NH3

Net Ionic:

NH4(+) + NH2(-) --> 2NH3

Pauline Tze 3B
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Re: Homework 12.9

Postby Pauline Tze 3B » Tue Nov 22, 2016 9:34 am

@Crystal

From looking at what Belicia wrote,

I believe I misinterpreted the question. I was finding the conjugate acid and conjugate base and the Bronsted acid and base at the same time and somewhere down the line I associated them as the same thing, so I thought then that it was necessary for 2NH3 to dissociate into 2NH2- and 2H+ but it actually isn't because the actual Bronsted base is the NH2- is the one on the reaction side, not the product side (if that doesn't make sense and you got the right answer don't worry about it).

I don't believe you need to worry about the dissociation of NH3, it should be rare because it is not an ionic compound but rather a covalent compound so it won't break down easily.


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