CHMA11H3 Lecture 10: CHMA11 Lecture 10

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CHMA11 Lecture 10: Characterizing Acids and Bases
- Polyprotic Acids: Acids that can produce more than one molecule of hydronium when
they dissociate
o These acids are able to ionize in multiple steps
Gives them multiple Acid Ionization constant (Ka) values
o Finding the pH of polyprotic acid solutions is thus slightly harder than in normal
acids
Key fact is that the first Ka value will always be much larger than the
second
Therefore we are able to use the first Ka value to get an initial pH
value
We can then use the second Ka value to solve for the pH as if we
were in a weak acid equilibrium using ICE tables
For strong polyprotic acids, the concentration of the acid initially will
equal the concentration of the acids once it undergoes its first
dissociation
Therefore for these strong acids if we know the initial
concentration, we will know the concentration of it after it
undergoes its first disassociation
We can then insert this concentration into the calculations for the
second ionization and solve for the hydronium concentration
using the second Ka value
o Will thus allow us to determine pH
- Classifying salt solutions as acidic, basic or neutral
o Since most salts will contain both a cation and anion, they are able to form
acidic, basic or neutral solutions when dissolved in water
o The pH of the solution depends on the specific cation and anion involved
o 4 potential possibilities
1: Salts in which neither the cation nor anion act as an acid or base will
form pH neutral solutions
This involves salts in which the cation is the counter ion of a
strong base
Also involves salts in which the anion is the conjugate base of a
strong acid
These salts form neutral solutions
Eg: NaCl, KBr
2: Salts in which the cation does not act as an acid and the anion acts as a
base will form basic solutions
Involves salts in which the cation is an alkali metal
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