Acids & Bases

1. Acids & Bases

2. When an acid dissolves (donating a proton) in water (acting as a base or proton acceptor), a proton is transferred from the acid to the water. HA(aq) + H2O(l)  H3O+(aq) + A-(aq) A new acid and base are formed.

3. The new acid is called the conjugate acid and the new base is called the conjugate base. HA (aq) + H2O (l)  H3O+(aq) + A-(aq) conjugate acid conjugate base

4. The conjugate acid and base can react with one another HA(aq) + H2O(l)  H3O+(aq)+ A-(aq) HA(aq) + H2O(l)  H3O+(aq)+ A-(aq) to reform the parent acit and water molecule.

5. There is a competition for the H+ ion between H2O in the forward reaction and A- in the reverse reaction. HA(aq) + H2O(l)  H3O+(aq)+ A-(aq)

6. HA(aq) + H2O(l)  H3O+(aq)+ A-(aq) If H2O wins the competition, the solution will contain mostly H3O+ and A-. The  reaction will dominate. HA(aq) + H2O(l)  H3O+(aq)+ A-(aq)

7. HA(aq) + H2O(l)  H3O+(aq)+ A-(aq) We can say that the HA is completely ionized or completely dissociated. The situation represents a strong acid

8. HA(aq) + H2O(l)  H3O+(aq)+ A-(aq) The opposite can also occur. Sometimes A- wins the competition for the H+. HA(aq) + H2O(l)  H3O+(aq)+ A-(aq) In this case A- is a much stronger base than H2O and the reverse reaction dominates

9. HA(aq) + H2O(l)  H3O+(aq)+ A-(aq) Here the A- has a much larger attraction for H+ than does H2O, and most of the HA molecules remain intact. This situation represents a weak acid.

10. HA(aq) + H2O(l)  H3O+(aq)+ A-(aq) The relationship of acid strength and conjugate base strength

11. A strong acid solution contains H+ ions and a strong base solution contains OH- ions. When a strong acid and strong base are mixed, the H+ and OH- react to form H2O. H+(aq) + OH-(aq) H2O(l) This is called a neutralization reaction because if equal amounts of H+ and OH- are available for reaction, a neutral solution ( pH = 7 ) will result.