Acid and Bases

Acid and Bases

1. Acid-base theories

   • Lewis
     • Acid - electron pair acceptor
     • Base - electron pair donor
   • Bronsted-Lowry
     • Acid - proton donor
     • Base - proton acceptor

2. Conjugate systems

   • Acids are related to bases
     • ACID <=> PROTON + CONJUGATE BASE
   • Bases are related to acids
     • BASE + PROTON <=> CONJUGATE ACID
   • For an acid to behave as an acid, it must have a base present to accept a proton
     • acid + base <=> conjugate base + conjugate acid
       • HA + B <=> BH+ + A-

3. pH = -log10[H+]

   • The smaller the pH, the greater the conc. of H+

4. pOH = -log10[OH-]

5. Kw = [H+][OH-]

   • water is weakly dissociated

6. Weak acids and bases

   • weak acids and weak bases dissociate only in aqueous solution
   • Ka = ([H+][A-]) / [HA]
     • Ka is the dissociation constant for a weak acid
     • Ka = [H+]2 / [HA]
   • The weaker the acid..
     • the less it dissociates
     • the fewer ions you get
     • the smaller Ka
   • pKa
     • very weak acids have very small Ka values
       • Its is easier to compare the strength as pKa
     • pKa = -log10 (Ka)

7. species that can act as an acid or base are amphoteric

8. Strong acids

   • a strong acid is one which dissociates completely in water into H+ and A-
   • Examples
     • HCl
     • HNO3
     • H2SO4
   • Strong acids do not dissociate fully at high concentrations
     • There is not enough water
     • diluting the acid tenfold causes the pH to increase by one unit

9. Titrations

   • Curves
   • Indicators

10. Buffers

    • A solution that resists change of pH when small amounts of acid or base are added or on dilution
    • Acidic buffers
      • They are made from a mixture of a weak acid and a soluble salt of that acid
      • It will maintain a pH of below 7
      • The weak acid component is to act as a source of HA to remove any added OH-
        • HA + OH- --> A- + H2O
      • The salt component is to act as a source of A- to remove any added H+
        • A- + H+ --> HA
    • It is possible to saturate a buffer
    • Basic buffers
      • It will maintain a pH of above 7
      • They are made from a mixture of a weak base and a soluble salt of that base
      • Aqueous ammonia and ammonium chloride acts as a bsic buffer
        • NH3 + H+ --> NH4+
        • NH4+ + OH- --> NH3 + H2O

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