| Sections | |||
|---|---|---|---|
| Identifying Acids and Bases | 52 mins | 0 completed | Learn Summary |
| Arrhenius Acid and Base | 7 mins | 0 completed | Learn Summary |
| Bronsted Lowry Acid and Base | 18 mins | 0 completed | Learn Summary |
| Amphoteric | 6 mins | 0 completed | Learn |
| Lewis Acid and Base | 14 mins | 0 completed | Learn Summary |
| pH and pOH | 64 mins | 0 completed | Learn Summary |
| Ka and Kb | 21 mins | 0 completed | Learn |
| Ionic Salts | 46 mins | 0 completed | Learn |
| Diprotic Acid | 31 mins | 0 completed | Learn Summary |
| Polyprotic Acid | 24 mins | 0 completed | Learn |
| Additional Practice |
|---|
| Strong Acid-Base Calculations |
| Weak Acids |
| Additional Guides |
|---|
| Strong Acids and Strong Bases |
| Conjugate Acids and Bases |
| Weak Bases |
A polyprotic acid possesses more than 2 hydronium ions (H+).
Polyprotic Acids
Our understanding of diprotic acids and bases can be used to understand polyprotic acids and bases.
Concept #1: The most common type of polyprotic acid is the triprotic acid, which contains 3 acidic hydronium ions.
Concept #2: Triprotic bases contain 3 Kb values, so they would have 3 equilibrium equations.
Concept #3: As a result of these equations for polyprotic acids and bases the relationship between Ka and Kb can be established.
Example #1: Determine the pH of 0.300 M sodium hydrogen phosphate, Na2HPO4. Phosphoric acid, H3PO4, contains Ka1 = 7.5 x 10-3, Ka2 = 6.2 x 10-8 and Ka3 = 4.2 x 10-13.
Example #2: Determine the pH of 0.300 M citric acid, H3C6H5O7 it possesses Ka1 = 7.4 x 10-4, Ka2 = 1.7 x 10-5 and Ka3 = 4.0 x 10-7.
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Additional Problems
Identify the triprotic acid.
A) HNO3
B) H3PO4
C) H2CO3
D) HFO4
E) H2SO4
Determine the pH of a 0.03 M solution of NaH 2PO4? Assume H3PO4 has a pKa1 of 2.1 and a pKa2 of 7.2 and a pKa3 of 12.7.
1. 4.36
2. 7.11
3. 4.65
4. 7.40
5. 9.95
6. 1.81
Consider a solution that is 0.10 M in a weak triprotic acid which is represented by the general formula H3A with ionization constants K1 = 1.0 × 10−3 , K2 = 1.0 × 10−8 , and K3 = 1.0 × 10−12. What is the pH of the solution?
1. 2.15
2. 2.25
3. 2.02
4. 2.35
5. 2.54
In a triprotic acid, which Ka has the highest value?
A) Ka1
B) Ka2
C) Ka3
D) Kb1
E) Kb2
Which below correctly describes the relationship amongst the successive p Ka and Kb values for most polyprotic acids?
a) pKa1 > pKa2 > pKa3
b) pKa3 > pKa2 > pKa1
c) Kb1 > Kb2 > Kb3
d) Ka1 < Kb1
e) cannot be predicted
In a triprotic acid which Ka value is largest in value?
a) Ka1
b) Ka2
c) Ka3
d) They are all equal.
For the polyprotic acid H3PO4 (phosphoric acid), which of the following expressions would correspond to Ka3?1. H3PO4 ⇌ PO43− + 3 H+2. PO43− + 3 H+ ⇌ H3PO43. HPO42− ⇌ PO43− + H+4. H2PO4− ⇌ HPO42− + H+5. H3PO4 ⇌ H2PO4− + H+
What is the pH of a solution of 0.25 M K3PO4, potassium phosphate? GivenKa1 = 7.5 * 10-3Ka2 = 6.2 * 10-8Ka3 = 4.2 * 10-13
Phosphoric acid (H3PO4) is characterized by three reactions for stepwise dissociation. Arrange the following species in the order of decreasing concentration in an aqueous solution of H3PO4. Clearly indicate the order of concentration change. JUSTIFY your answer.H3PO4 H 2PO4- HPO 42- PO 43- H 3O+
Identify the weak triprotic acid.A) CH3COOHB) H3PO3C) H3PO4D) H2SO4E) H2SO3
Citric acid, which is present in citrus fruits, is a triprotic acid (Ka1 = 7.4x10-4, Ka2 = 1.7x10-5, Ka3 = 4.0x10-7). Is the concentration
of citrate ion (C6H5O73–) equal to, less than, or greater than the H+ ion concentration?
What is the equilibrium associated with Ka3 for H3PO4?
Write out the stepwise Ka reactions for citric acid (H3C6H5O7), a triprotic acid.
Arsenic acid (H3AsO4) is a triprotic acid with K a1 = 5.5 X 10 -3, Ka2 = 1.7 X 10 -7, and Ka3 = 5.1 X 10-12. Calculate [H+], [OH-], [H3AsO4], [H2AsO4-], [HAsO42-], and [AsO43-] in a 0.20-M arsenic acid solution.
Citric acid has four hydrogens bonded to oxygen. How does the hydrogen that is not an acidic proton differ from the other three?
Write corresponding equilibrium expressions for third ionization step of phosphoric acid.
Calculate the [H3O+] and pH of each polyprotic acid solution.a. 0.125 M H2CO3b. 0.125 M H3C6H5O7
For phosphoric acid, H3PO4, the pKas are:pKa1 = 2.2pKa2 = 7.2pKa = 12.7a) Write the reaction associated with K a2.b) Write Ka2 in terms of the concentration of the reactants and products in the reaction above?c) To make a buffer that is close to neutral pH, how would you use some of the following. Be precise in terms of what you would use and how much of each.0.001 M HCl, 1 M HCl, 10 M HCl0.001 M H3PO4, 1 M H3PO40.001 M NH3, 1 M NH3WaterSolids: Fe, Na, NaCl, NaH, NaOH
Using chemical equations, show how the triprotic acid H 3PO4 ionizes in water. Phases, such as (I) or (aq), are optional. Please explain each step in detail.__________________ Ka1 __________________ Ka2 __________________ Ka3
Which of the following represents the correct relative Ka values for H3PO4 (Ka1), H2PO4- (Ka2) and HPO42- (Ka3)?A. Ka1 = Ka2 = Ka3B. Ka1 < Ka2 > Ka3C. Ka1 < Ka2 < Ka3D. Ka1 > Ka2 > Ka3E. None of the above
Using chemical equations, show how the triprotic acid H3PO4 ionizes in water. Phases, such as (I) or (aq), are optional. Each successive ionization reaction removes an H+ ion, so the final reaction should produce the unprotonated PO43- ion.
Phosphoric acid is a triprotic acid (Ka1 = 6.9 x 10-3, Ka2 = 6.2x 10-8, and Ka3 = 4.8 x10-13). To find the pH of a buffer composed of H2PO4- (aq) and HPO42- (aq), which pKa value would you use in the Henderson-Hasselbalch equation?Calculate the pH of a buffer solution obtained by dissolving 13.0 g of KH2PO4(s) and 26.0 g of Na2HPO4(s) in water and then diluting to 1.00 L.
Farmers who raise cotton once used arsenic acid, H3AsO4 , as a defoliant at harvest time. Arsenic acid is a polyprotic acid with K1 = 2.5 x 10-4 , K 2 = 5.6 x 10-8 , and K3 = 3 x 10-13 . What is the pH of a 0.500 M solution of arsenic acid?A) 0.85B) 1.95C) 3.90D) 4.51