Acids and Bases
Acid-Base chemistry is important in a wide variety of applications.
ex: acid rain, blood pH, aquariums, etc...
➞ acids - sour taste
➞ bases - alkalis, taste bitter, slippery (soap, Drano)
Arrhenius Acids and Bases
Arrhenius Acid = a substance that produces H+ ions (protons) in aqueous solutions.
Arrhenius Base = a substance that produces OH- ions in aqueous solutions.
The above two definitions are limited to only aqueous solutions. The Bronsted-Lowry definitions, however, are not as limited...
Bronsted-Lowry Acids and Bases
Bronsted-Lowry Acid - a substance that is a proton (H+) donor.
Bronsted-Lowry Base - a substance that is a proton (H+) acceptor.
Check out the example below. You can see that H2O is acting as a Bronsted-Lowry base.
It has a lone pair of electrons that can "grab" or "accept" HCl's proton (H+ ion)...
Now, I want to show you a typical acid-base reaction that ends up with products that can be labeled as a conjugate acid and a conjugate base.
Here are the definitions of each...
Conjugate Acid-Base Definitions
Conjugate Acid = formed when a proton (H+) is added to the base.
Conjugate Base = this is what's "left over" after the acid has its H+ (proton) removed.
Conjugate Acid-Base Pairs
NOTES - Here's 4 key points about the above generalized reaction. The 3rd note is a bit lengthy.
1. HA and A- are a conjugate acid-base pair.
2. H2O and H3O+ are a conjugate acid-base pair.
3. The above reaction is essentially a competition for the proton (H+) between the two bases (A- and H2O).
Here's the equilibrium expression for the above reaction:
➞ If H2O is a much stronger base than A-, then the equilibrium lies to the right (larger Ka).
Why? Because H2O is "better than" A- at "grabbing" or accepting a proton (H+) in the reaction. On the other hand...
➞ If A- is a much stronger base than H2O, then the equilibrium lies to the left (smaller Ka).
Why? Because being the stronger base, A- is "better than" H2O at "grabbing" or accepting a proton (H+) in the reaction.
4. Because H2O(l) is not included in the equilibrium expression, the Ka has the same form as that for the simple dissociation reaction:
HA (aq) ⇌ H+ (aq) + A- (aq)
( but don't forget the role of H2O ).
My next video post from SECTION 14 - Acids and Bases will cover Acid Strength and Conjugate Acid-Base Examples and Practice Problems.