- Note: stronger acid/base = less stable
X-H Acids
For X-H acids, there are two factors for acid strength
- Bond Strength (between H and other atom): low = strong acid bcuz H can easily dissociate
- Compare bond dissociation energies 2. Bond Polarity (high → weak acid)
- The greater the difference in electronegativity between these two elements, the more polar the bond will be → more polar bond → stronger X-H bond = weaker acid
- For X-H bonds, acid strength increases going down a column because the electronegativity of the elements bonded to hydrogen decreases
○ Greater electronegativity of other element = weaker acid
Oxyacids
- Acid that has oxygen, hydrogen, and at least another element ○ The Hydrogen is always bonded to Oxygen
- With oxyacids, acid strength increases with an increase in the number of oxygen atoms
○ Why? Oxygens are very electronegative → causes the electron density to be greater and more pulled towards the oxygen side which weakens the bond between H and O
- Compare compounds with same number of oxygens but diff elements → more electronegative element = compound will have greater electron density → weaker O-H bond → stronger acid
- For oxyacids, acid strength decreases going down a group because the electronegativity of the central atom decreases
Bases
- Base with more electronegative element = weaker base b/c will be a poorer proton acceptor
- Base with larger Kb value (stronger base) = weaker/more stable conjugate acid = conj acid has less electronegative element
Determining the pH of a Mixture of Acids
- The process is the same: determine the major species and the stronger (bigger Ka) will dominate
- If both acids are weak → the acid with the larger Ka is slightly stronger → when calculating pH only need to focus on (make ICE table) for dominant acid
- Strong acid + weak acid → focus on strong acid
- Strong acid + strong acid → have to do both
Complex Ions
- Complex ion: a charged species consisting of a metal ion surrounded by ligands → produces an acidic solution
○ The higher the charge on the metal ion, the stronger the acidity of the hydrated ion.
- Ligand: a Lewis base