5/21/2013

Hi!

Yesterday, I covered Acids and Bases in general chemistry. I am reviewing with Berkeley review mcat books so it was section four in the first general chemistry book. Here is an overview of what was covered:

Acids and Bases

A. Acid - Base equilibria
    1. Bronsted - Lowry definition of acids and bases
           - Bronsted lowry acid = proton donor; B/L base = proton acceptor
     2. Ionization of water
                   a. Kw, its approximate value (Kw = 10^-14 @ 25 degree c)
                   b. pH definition, pH of pure water = 7.0
                                - pH is equal to the -log[H3O+]; @ pH of 7 [H3O+] = [OH-] ;
                                    @25 degrees pH + pOH = 14
     3. Conjugate acids and bases
           - conjugate acids/basis come in pairs; eg. H2SO4 and HSO4- are conjugate pairs, H2SO4 is the conjugate acid while HSO4- is the conjugate base
      4. Strong acids and bases
      5. weak acids and bases
                   a. dissociation of weak acids and bases with or without added salt
                    b. hydrolysis of salts of weak acids or bases
                            - refer to Ka or pKa of each weak acid; pKa = -log[Ka]
                    c. calculation of pH of solutions of weak acids or bases
                             - pH = pKa/2 - log[HA]; pOH = pKb/2 - log[A-]
     6. Equilibrium constants Ka and Kb
     7. Buffers
                  a. definition, concepts (common buffer systems)
                          - buffers consist of weak acid or weak base conjugate pairs that stabilize the pH when the conjugate pair is in approximately equal concentrations
                  b. influence on titration curves
                           - within a buffering region, the change in pH will decrease while the the volume of acid/base used will increase
                           - when a strong acid titrates  a strong base, the graph will be sinusoidal and the equivalence point will land at pH=7
                           - when a weak acid is titrated with a strong base, the equivalence point will be basic; when a weak base is titrated with a strong acid, the equivalence point will be acidic
                           - in a strong/strong titration, pH changes the most once the pH is at 7; in a weak/strong titration, pH will change the most initially, but once it reaches the buffering zone, pH changes will be minimal
                           - a buffering zone for a conjugate pair buffer will be the pKa +/- 1; e.g. for a pair with a pKa of 5, this buffer will work the best between the pH of 4 and 6

B. Titration
      1. Indicators
               - indicators usually change color as the pH changes; this occurs because the indicator comes in two different forms, protonated and deprotonated; when the pH of the solution is less than the pKa of the indicator, the indicator is protonated; when the pH of the solution is greater than the pKa of the indicator, the indicator is deprotonated. This change in the protonation of the indicator will cause a change in the color of the indicator. When the pH = pKa of the indicator, there will be a mixture of colors between the protonated color and the deprotonated color.
      2. Neutralization
      3. Interpretation of titration curves