Okay seems like you have it down. I had my doubts because one of your first answers were that acetate will make the solution more acidic but that may have just been a typo or hasty reply.
So now onto sodium bicarbonate.
Because CO
3 has a (-2) charge it can accept 2 protons and become H
2CO
3. This is what is known as a polyprotic acid. Poly because it has more than one acidic proton. Other examples are sulfuric acid and phosphoric acid, which have 2 and 3 acidic protons respectively.
Now what NaHCO
3 can do in solution is this. When you dissolve the salt you will get Na+ and HCO
3-. You are correct in that Na+ just sort of hangs out and does nothing but you then have a substance which is amphoteric (meaning can act as both a base and acid). Depending on the pH of the solution the bicarbonate anion can let go of its last proton to form CO
3(-2) or it can become protonated to form carbonic acid (H
2CO
3). These species are all in equilibrium and the equilibrium will shift depending on pH of solution (IOW how much H+ or OH- is floating around). Another confounding factor to all of this is the fact that carbonic acid is not stable and readily decomposes into carbon dioxide and water.
So it somewhat looks like this
H
2O + CO
2 ⇌ H
2CO
3 ⇌ H+ + HCO
3- ⇌ 2H+ + CO
3(-2)
Therefore when you put sodium bicarbonate (a salt of Na+ and HCO
3-) into something like vinegar it completely dissociates to give the two ions, the Na+ does nothing, but the bicarbonate anion will become protonated and then decompose in water and carbon dioxide. Every High School kid sees a demonstration of baking soda plus vinegar giving you a cool bubbling effect. Thats from the evolution of carbon dioxide gas. If you have a basic solution the equilibrium gets pushed to the opposite side, the bicarbonate is deprotonated.
PEZenfuego said:
My understanding is that once Na+ dissociates it is done reacting. It just sticks around as a spectator. So why when I combine H2CO3 and NaOH do we get sodium bicarbonate? Don't the sodium ions want to dissociate from the hydroxide and call it a day?
What we get is really a matter of what the pH of solution is. Do you know about pKa's and Keq's yet? Hydroxide can deprotonate the second acidic hydrogen of bicarbonate yielding a CO
3(-2). If all ions stay in solution (meaning no precipitate forms) you don't really get Na
2CO
3 as water will solvate both of the ions and they will be separate from each other. However if you, say, evaporate all the solvent and recover crystals these crystals will now be Na
2CO
3 and will only act as a base if re-dissolved in new solvent.
So basically even though acids and bases can be considered as salts they don't behave exactly as salts. All salts completely dissociate (assuming adequate solubility) while acids that are not considered strong acids will not dissociate fully. NaCl behaves as a salt and fully dissociates (the fact that nothing happens afterward is because they are the conjugates of strong acids/bases). Acetic acid does not fully dissociate and an equilibrium exists between the acid and the conjugate base.
Whenever you think of these things consider what you have in the flask. Salts will fully dissociate but then you may have the conjugate base of a weak acid which then may act as a base and become protonated (if the solution is acidic). Then you may have the case of amphoteric molecules which can "go both ways." Which way they go depends on conditions.
Take away is this: Salts always fully dissociate in solution (assuming they are soluble) but acids do not. Salts and acids are not exactly the same thing and behave differently. Sodium bicarbonate is a salt but when it fully dissociates it gives you something that is not a strong acid and can deprotonate or become protonated (because it "goes both ways").
Hope this helps.
