1. Unit 6: Acid-Base Equilibria

2. What are Acids and Bases?
First off, we will watch an introduction video, made by a film-producing genius, in order to be reminded briefly about what acids and bases actually are. I am sorry if this video ruins your life.
Is it starting to come back to you?

3. Physical Properties of Acids and Bases
Acids are corrosive – this means that they can corrode things, or break them down.
Acids have a pH that is below 7 – we will talk much more about pH later.
Acids taste sour, and can be found in fruits and juices.
Acids are good conductors of electricity, we will learn why soon.
Bases are also corrosive
Bases have a pH that is above 7 – note that a pH of 7 is neutral (water)
Bases taste bitter, and are present in things like soap
Bases are very slippery to the touch
Bases are also good conductors of electricity

4. Chemical Properties of Acids
Acids turn litmus paper red. When you are checking whether or not a compound is acidic, you use blue litmus paper.
Bases turn litmus paper blue. When you are checking whether or not a compound is basic, you use red litmus paper.
Acids react with metals to form hydrogen gas. The metals are dissolved and form an ionic compound in solution during this process.

5. Arrhenius Model of Acids and Bases
In 1883, a Swedish man named Svante Arrhenius proposed a simple definition of acids and bases that seemed to explain a great deal of the tendencies of acids.
Arrhenius proposed that an acid is any substance that dissolves in water to produce hydrogen ions, H+.
Arrhenius also proposed that a base is any substance that dissolved in water to produce OH- ions.

6. Is Water Acid or Base? H2O < - - > H+ + OH-
Water is always dissociating and recombining in a state of chemical equilibrium. At any one time, all three of the following species are present in a solution:
H2O < - - > H+ + OH-
Water is a neutral substance, meaning that it is not an acid or a base. Soon, we will learn that in some ways, it’s both.

7. Arrhenius Model HCl  H+ + Cl- NaOH  Na+ + OH-
This worked really well for some acids and bases. For instance, it explained the acidic properties of HCl and the basic properties of NaOH quite well:
HCl  H+ + Cl-
NaOH  Na+ + OH-

8. Arrhenius Goes Wrong
Arrhenius’ model could not explain the basic properties of many substances, however.
For instance, it was well known that a solution of NH3 produced hydroxide ions in water, and yet there is not any oxygen present in an NH3 molecule!
Other molecules also posed a problem for this model, such as CO3-. Therefore, a modified version of acid-base theory was required.