Ionization vs Dissociation: similarities and Differences
Acid-Base Questions are Equilibrium Questions
The most important thing for you to recognize is that almost ALL acid base questions are about equilibrium.
Where does Ka come from? From the equilibrium from NH4+, an acid, and NH3, its conjugate base:
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And Kb comes from the equilibrium between a base and its conjugate acid:
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Arrhenius Acids: An "Outdated" Idea
The Arrhenius definition of an acid is: Anything that gives off H+ when in water.
* To be an Arrhenius acid, the formula MUST HAVE an H in its formula, and
* that H must (generally) be attached to an electronegative atom like N, O, F or Cl.
* To be an Arrhenius acid, the formula MUST HAVE an H in its formula, and
* that H must (generally) be attached to an electronegative atom like N, O, F or Cl.
H3PO4 is an Arrhenius acid because H3PO4 + H2O → H3O+ + H2PO4-
HNO3 is an Arrhenius acid because HNO3 + H2O → H3O+ + NO3-
CH3COOH is an Arrhenius acid because CH3COOH + H2O → H3O+ + CH3COO-
HNO3 is an Arrhenius acid because HNO3 + H2O → H3O+ + NO3-
CH3COOH is an Arrhenius acid because CH3COOH + H2O → H3O+ + CH3COO-
Bronsted-Lowry Acids: Most High School Students use This
The Bronsted-Lowry definition of an acid is: Anything that donates H+ to anything else
Lewis Acids: Most University Students use This
Lewis Acids are electron pair acceptors
Lewis Bases are electron pair donors. Consider this reaction: NH3 + H2O → NH4+ + OH- The NH3 donated a pair of electrons to the H, which came off of the water.
Lewis Bases are electron pair donors. Consider this reaction: NH3 + H2O → NH4+ + OH- The NH3 donated a pair of electrons to the H, which came off of the water.
- NH3 is the Lewis Base
- H2O is the Lewis Acid
Ionization and Dissociation: Similarities and Differences
Ionization is the process of creating ions where there were none before. Weak Brønsted-Lowry acids, such as HCl, CH3COOH and HCN are covalent compounds, which mean their atoms are sharing electrons and there are no ions. When they react with water, however, the hydrogen atom is (For some percentage of the molecules, anyways) transferred or “donated” to the water molecule. This creates two ions: Hydronium (H3O+) and the conjugate base (Cl-, CH3COO- or CN- according to the examples above). This creation of ions is card Ionization.
When an ionic compound dissolves in water, the ions are simply being separated from one another. Table salt, sodium chloride, is already made of Na+ ions and Cl- ions in a crystal lattice. Dissolving salt in water frees these ions from each other, but they were already ions - none were created. This separation of already-existent ions is called Dissociation.
When an ionic compound dissolves in water, the ions are simply being separated from one another. Table salt, sodium chloride, is already made of Na+ ions and Cl- ions in a crystal lattice. Dissolving salt in water frees these ions from each other, but they were already ions - none were created. This separation of already-existent ions is called Dissociation.
