neutralization with salt

[chiddler]

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Al(OH)2NaCO3

how many acidic protons can be neutralized per molecule?

I figured that Al(OH)2 is insoluble in water which only leaves the carbonate = 2 protons. But it's 4; their answer suggests that Al(OH)2 is soluble, too.

Why should aluminum hydroxide be considered as basic?

 

[MedPR]

Al(OH)2NaCO3

how many acidic protons can be neutralized per molecule?

I figured that Al(OH)2 is insoluble in water which only leaves the carbonate = 2 protons. But it's 4; their answer suggests that Al(OH)2 is soluble, too.

Why should aluminum hydroxide be considered as basic?

I don't get it either, but I can tell you that Al(OH) is soluble in acidic solution. Not sure if that will help though.

 

[IH8ColdWeath3r]

hydroxide is definitely soluble in water and it can neutralized protons. In the compound that you presented, there are 2 OH so that accounts for 2 protons, and carbonate is a base that has the capability of neutralized another 2 protons

CO3 + H ==> HCO3 + H ==> H2CO3.

Therefore, 4 acidic protons can be neutralized.

 

[FearlessHyena]

Al(OH)2NaCO3

how many acidic protons can be neutralized per molecule?

I figured that Al(OH)2 is insoluble in water which only leaves the carbonate = 2 protons. But it's 4; their answer suggests that Al(OH)2 is soluble, too.

Why should aluminum hydroxide be considered as basic?

The answer is 4. The reason is that although Al(OH)2 is slightly soluble, by putting it in acid, you get more of it to dissolve. The 2OH- will react with 2H+ to make H20. This reduces OH- concentration, which causes more to dissolve. You already understand the CO3. This is the idea with the common ion effect. When we have a basic compound, we can increase its solubility by placing it in an acid, or vice versa. Also, this is why an basic compound won't dissolve as much when it's placed in basic conditions because the OH- is high.

Finally, metal hydroxides are bronsted-lowry bases. The OH- when dissolved acts as a base. Metal oxides are lewis bases. By metals, I mean group 1 and group 2. MgO+ H2O= Mg(OH)2 basic . We have converted a lewis base into a bronsted-lowry acid.

Non-metal oxides, such as CO2, are lewis acids. They react with water to form bronsted-lowry acids. Acid rain, which is formed when non-metal oxides like SO3 react with H2O to form H2SO4, is the result of converting a lewis acid into a bronsted-lowry acid.

 

[chiddler]

so all insoluble hydroxides can be dissolved with acid because the OH is consumed by acidic proton causing equilibrium to progress to the right?

@UTSA you're incorrect, my friend. Look:

http://en.wikipedia.org/wiki/Aluminium_hydroxide

Solubility in water: 0.0001 g/100 mL (20 °C)

 

[IH8ColdWeath3r]

hmm yeah I saw that. It says soluble in acids but its solubility in water is essentially non-existent.

 

[mcloaf]

hmm yeah I saw that. It says soluble in acids but its solubility in water is essentially non-existent.

It doesn't need to be highly soluble to neutralize acid. If the tiny amount that goes into solution is instantly going to be consumed then the equilibrium will keep moving to the right and dissolving more.

 

[chiddler]

It doesn't need to be highly soluble to neutralize acid. If the tiny amount that goes into solution is instantly going to be consumed then the equilibrium will keep moving to the right and dissolving more.

does this apply to all water insoluble hydroxides?

 

[mcloaf]

does this apply to all water insoluble hydroxides?

I can't imagine when it wouldn't. I guess you could try to limit it by saturating the solution with another salt containing the spectator cation (in this case Al), but even then I think the favorability of the neutralization would still pull the equilibrium forward and just precipitate whatever other Al salt you had in there.

This seems to me to be, on a fundamental level, just an unfavorable reaction coupled to a more favorable reaction of the products, which will pull the solvation reaction forward. This is what makes carbohydrate metabolism and many other physiological reactions possible.

 

[chiddler]

I can't imagine when it wouldn't. I guess you could try to limit it by saturating the solution with another salt containing the spectator cation (in this case Al), but even then I think the favorability of the neutralization would still pull the equilibrium forward and just precipitate whatever other Al salt you had in there.

This seems to me to be, on a fundamental level, just an unfavorable reaction coupled to a more favorable reaction of the products, which will pull the solvation reaction forward. This is what makes carbohydrate metabolism and many other physiological reactions possible.

i understand, thanks very much.