CHMA11H3 Lecture Notes - Lecture 8: Acid Strength, Nitric Acid, Sulfuric Acid
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23 Jan 2019
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CHMA11 Lecture 8: The Acid Ionization Constant (Ka)
- Characterizing Acid Strength
o Strong and weak acids are defined based on their ability to dissociate into its
component ions
▪ Strong acids: will completely ionize in solution
▪ Weak acids: will partially ionize in solution
▪ The strength of an acid can be represented by equilibrium of said acid
• If equilibrium of the acid lies far to the right, the acid is said to be
strong
o It will completely ionize
• If equilibrium of the acid lies far to the left, the acid is said to be
weak
o Only a small percentage of it will ionize
• The range of acid strength is continuous but for most purposes
the categories of strong or weak are useful
o Strong vs Weak Acids
▪ Strong acids
• There are 6 key strong acids
o HCl, HBr, HI, HNO3, HClO4, H2SO4
• Monoprotic Acids: acids containing only one ionisable proton
o HCl, HBr, HI, HNO3, HClO4
• Diprotic Acids: acids containing two ionisable protons
o H2SO4
▪ Weak acids
• There are 6 key weak acids
o HF, CH3COOH, HCOOH, H2SO3, H2CO3, H3PO4
▪ Denoting between strong and weak acids
• The degree to which an acid is strong or weak depends on the
attraction between the anion of the acid (the conjugate base) and
the hydrogen ion relative to the attraction of these ions to water
o If the attraction between the anion and hydrogen is weak,
then the reaction favors the forward direction and the
complete dissociation of the acid is enabled
▪ The acid is thus deemed strong
o If the attraction between the anion and hydrogen is strong
then the reaction favors the reverse direction
▪ Enables only partial dissociation of the acid
▪ The acid is thus deemed weak
• The stronger the acid, the weaker the conjugate base and vice
versa