Destroyer GenChem question

[drill-and-fill]

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Question 26. Which of the following compounds would be most soluble in NH3?

K2CO3
NaBr
AgBr
CaCl2
LiNO3

The answer is AgBr. I read the solution in the back, and I also read other threads pertaining to this question so I kinda see why AgBr would be most soluble.. (AgBr is acidic, NH3 is basic)

However, I remember Chad saying that compounds containing Pb, Ag, Hg are not soluble and my question is, why does that rule NOT apply here? Because of that rule, the first thing i did was to cross out AgBr as a possible answer.

Even the destroyer says in a solution for another question to be aware of compounds containing Ag, Hg, and Pb because theyre insoluble and will form a precipitate...

Can someone explain why the solubility rule doesnt apply here??

 

[mrg276]

Question 26. Which of the following compounds would be most soluble in NH3?

K2CO3
NaBr
AgBr
CaCl2
LiNO3

The answer is AgBr. I read the solution in the back, and I also read other threads pertaining to this question so I kinda see why AgBr would be most soluble.. (AgBr is acidic, NH3 is basic)

However, I remember Chad saying that compounds containing Pb, Ag, Hg are not soluble and my question is, why does that rule NOT apply here? Because of that rule, the first thing i did was to cross out AgBr as a possible answer.

Even the destroyer says in a solution for another question to be aware of compounds containing Ag, Hg, and Pb because theyre insoluble and will form a precipitate...

Can someone explain why the solubility rule doesnt apply here??

I'm pretty sure that those compounds are not soluble unless they pair up with the conjugate base of one of the strong acids... i.e. HBr is a strong acid, Br- is it's conjugate base; therefore, AgBr will be soluble.

Someone might want to double check this though.

 

[EpicDentist]

Ag is a transition metal and forms a complex ion with NH3 that's very soluble

http://www.ars-chemia.net/Classes/102/Notes/Transition_Metals.pdf

 

[drill-and-fill]

So... when you mix Pb, Ag, or Hg with NH3, forget about the solubility rule?

 

[dent4]

Since AgBr is an acidic salt it will react with the basic NH3 giving HBr which is an acid. I do remember chad saying Ag, Pb, and Hg are insoluble in MOST, but since it's an acidic salt it will be soluble in the basic solution b/c he did say acid salts are soluble in basic solutions and vice versa.

 

[Dgeorg6]

I may be completely wrong in this, but doesn't chad say that those elements (Ag, Hg, and Pb) are insoluble in water? If so this question is asking what is more soluble in NH3.. Again, I didnt look back at my notes so I could be completely wrong lol

 

[dent4]

I do agree with you, I remember him say the exact same thing that's why I put CaCl2 when I ran into this problem; however I do remember him saying that if an acidic/basic salts are always soluble in basic/acidic solutions. I could be completely wrong but I believe that strength of the acidity HBr will make it soluble. Not 100% but that's what I got out of it. Watch me be completely wrong lol but idk I think it makes sense.

 

[NDPitch]

I asked this very question to Chad. He responded...

This question is beyond the scope of the DAT (or the average college gen chem class for that matter). Ammonia can form "complex ions" with a number of transition metal ions including silver (the only salt with a transition metal ion out of the answer choices); but this isn't something you'll be required to know on the DAT. Ultimately as AgBr(s) dissolves the silver ions formed complex with the ammonia forming Ag(NH3)2+. This decreases the amount of free Ag+ in solution causing more AgBr(s) to dissolve according to Le Chatelier's Principle.

Again, this is beyond the scope of the DAT. Hope this helps!

 

[drill-and-fill]

Thanks guys! You guys are the bestest 😀

 

[sagarkanodiya]

Solubility rules apply to only compounds soluble or insoluble in water not any other solvent. Here the solvent is Ammonia. I agree to all above posts that this question is way beyond the scope of DAT.

 

[EpicDentist]

I don't agree that it's "beyond the scope of the DAT," as this was taught in my college gen chem class. Plus, the ADA website says "Chemical Equilibria - molecular, acid/base, precipitation, calculations, and Le Chatelier's principle."

In my opinion this topic fits in that criteria, but study according to YOUR standards, not from hearsay that Chad is telling you. The last thing you want is to be sorry b/c you "skimped" on a few topics.

P.S.: It is explained beautifully in this Purdue gen chem class website for Complex Ions
http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch18/complex.php#complex

 

[lavashak]

I thought I am one of the few people who still study for DAT