Strong Acid/Strong Base pH 7 Water Strong Acid Equivalence Pt. mL of base added
Weak Base/Strong Acid Weak Base pH Conjugate Acid <7 Equivalence Pt. Strong Acid mL of acid added
Weak Acid/Strong Base Strong Base pH Conjugate base >7 Weak Acid Equivalence Pt. mL of base added
Indicators: generally complex molecules that are themselves weak acids in which the acid and conjugate base form exhibit different colors in solution
If Ka for the acid form of an indicator is 1 x 10-9 and the indicator is dumped into an acid solution with a pH = 0, what form of the indicator would be noticed?
If Ka for the acid form of an indicator is 1 x 10-9 and the indicator is dumped into an acid solution with a pH = 0, at what pH would the base form of the indicator become visible if base was added to the acid to increase the pH?
If Ka for the acid form of an indicator is 1 x 10-9 and the indicator is dumped into an acid solution with a pH = 0, at what pH would the base form of the indicator become dominant if base was added to the acid to increase the pH?
Phenolphthalein changes in this range pH Strong Acid/Strong Base Phenolphthalein changes in this range pH Bromthymol blue changes in this range 7 Note: Phenolphthalein would do a good job but bromthymol blue could be better. Equivalence Pt. mL of base added
Equivalence Pt.- When the titrant added is exactly enough to consume the substance being titrated. AKA…the stoichiometric endpoint Endpoint of the Titration – When the indicator undergoes a color change. The Endpoint of the Titration best reveals the Equivalence Pt. when the indicator used has a pKa that is very similar to the pH at the equivalence pt.
Weak Acid/Strong Base pH Alazarin Yellow R changes in this range. 11.1 Equivalence Pt. mL of base added
Diprotic Indicators H2Ind + H2O ↔ H3O+ + HInd- (Yellow) (Orange) HInd- + H2O ↔ H3O+ + Ind2- (Orange) (Blue) For H2Ind; pKa ≈ 6.4 For HInd-; pKa ≈ 11.7 @ pH = 0 Ka1 = 10-6.4 = [HInd-] = 1 1.0 1.0 [H2Ind] ~1 million
Yellow Diprotic Indicators H2Ind + H2O ↔ H3O+ + HInd- (Yellow) (Orange) HInd- + H2O ↔ H3O+ + Ind2- (Orange) (Blue) For H2Ind; pKa ≈ 6.4 Yellow For HInd-; pKa ≈ 11.7 @ pH = 0 Ka2 = 10-11.7= [Ind2-] = 1 1.0 1.0 [Hind-] ~1 trillion
Diprotic Indicators H2Ind + H2O ↔ H3O+ + HInd- (Yellow) (Orange) HInd- + H2O ↔ H3O+ + Ind2- (Orange) (Blue) For H2Ind; pKa ≈ 6.4 For HInd-; pKa ≈ 11.7 @ pH = 8 Ka1 = 10-6.4 = [HInd-] = ~ 100 10-8 10-8 [H2Ind] 1
Orange Diprotic Indicators H2Ind + H2O ↔ H3O+ + HInd- (Yellow) (Orange) HInd- + H2O ↔ H3O+ + Ind2- (Orange) (Blue) For H2Ind; pKa ≈ 6.4 Orange For HInd-; pKa ≈ 11.7 @ pH = 8 Ka2 = 10-11.7= [Ind2-] = ~ 1 10-8 10-8 [HInd-] 10000
Diprotic Indicators H2Ind + H2O ↔ H3O+ + HInd- (Yellow) (Orange) HInd- + H2O ↔ H3O+ + Ind2- (Orange) (Blue) For H2Ind; pKa ≈ 6.4 For HInd-; pKa ≈ 11.7 @ pH = 13 Ka1 = 10-6.4 = [HInd-] = ~107 10-13 10-13 [H2Ind] 1
Blue Diprotic Indicators H2Ind + H2O ↔ H3O+ + HInd- (Yellow) (Orange) HInd- + H2O ↔ H3O+ + Ind2- (Orange) (Blue) For H2Ind; pKa ≈ 6.4 Blue For HInd-; pKa ≈ 11.7 @ pH = 13 Ka2 = 10-11.7= [Ind2-] = ~100 10-13 10-13 [HInd-] 1