Titration of Strong Monoprotic Acid and Base

Polyprotic Acids

How to solve Ka expression for Polyprotic Acids?

Polyprotic Acids/Bases

Bethany Storro

• polyprotic acid can donate more than one proton• polyprotic base can accept more than one proton

H2SO4Ba(OH)2

Equilibrium Expressions for Polyprotics

• Ka1 = ionization constant for the first hydrogen atom

H2S(aq) + H2O(l) H3O+(aq) + HS-(aq)

• Ka2 = ionization constant for the second hydrogen atom

HS-(aq) + H2O(l) H3O+(aq) + S2-

Ka1 compared to Ka2

• If the difference between the Ka1 and the Ka2 values is 103 or more, the pH generally depends only on the first dissociation.

• Unique among common acids• STRONG in is first dissociation step ( ≥1.0 M)• WEAK acid in the second step (use quadratic)

Typical Titration with Weak Monoprotic Acids

Do the Structure, Initial Concentration of A/B influence pH ?

• Investigate your designated question• Design a series of investigations involving

titrations• Analyze titration curves• Pool data/Compare data with others• Answer primary question of lab

Available Materials• 0.2 M HCl• 0.1 M H2SO4

• 0.05 M HNO3

• 0.1 M HC2H3O2

• 0.2 M NH3

• 0.1 M NaOH• 0.1 M Ca(OH)2

• Stir rod• 2 x 100 mL grad. cylinders• 2 x 250 flasks

• Ring • pH strips, probe• 2 x 50 mL burets + clamp

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