[galpinj]

Hey guys,

I was looking at a question online which asked "which of the following compounds would be most soluble in ammonia?"
A. NaBr
B. AgBr
C. LiNO₃

The answer, in this case, was B because of the complex ion that can form with Ag⁺. I understand that, when broken apart, the other two salts can be considered "neutral salts" (Na⁺, Li⁺, NO₃^-, and Br^-), whereas Ag⁺ would be an acidic salt. This was commonly cited as the reason why B is correct, as ammonia would happily complex with the acidic salt, but I find this information a little sub-par.

NH₃, like H₂O, can both participate in hydrogen bonding and act as a base. The silver cation can also complex with water to form Ag·(H₂O)₂ in much the same way ammonia complexes with the silver cation. However, if one looks at the solubility rules, it's normally stated that silver, lead, and mercury are not readily soluble with group 7 elements (i.e. AgBr prior to dissociation).

Furthermore, even if we neglect this rule and assume AgBr is soluble, I still do not understand why an ionic compound like NaBr would not also be fully soluble. Both water and ammonia can participate in hydrogen bonding, so it seems reasonable to assume that sodium bromide would be soluble in ammonia (as it clearly is in water).

To be honest, these rules for acids and bases, solubility, and redox often all seem terribly intertwined and, despite many months of studying, I am still having trouble truly discerning what's going on when I look at chemical reactions. It's more than a little disheartening. Yesterday I was looking at a single displacement reaction, which uses the activity series, and I realized that it has a close parallel with reduction potentials. Situations like this just make everything all the more confusing.

Anyways, any input on my question would be very much appreciated! Is there any way to predict solubility when the solvent is not water? Are there any general rules or guidelines we can follow (hydrogen bonding, polarity, etc)?

Thank you

[jasongnome]

Looks to me like a very badly worded question. Ammonia is a gas at STP, so I assume it's talking about ammonia solution, in which case it's really reactivity rather than solubility it's asking about.

A and C woud both dissolve in the water that the ammonia is dissolved in anyway.

I assume B is the answer because it can, as you say, complex with the ammonia.

Where did you find this question?