Question 1

Which is NOT true for isoelectric and isoionic pH?

Accepted Answer

A) Isoionic pH is the pH of the pure,neutral,polyprotic acid. 
B) Isoelectric pH is the pH at which average charge of the polyprotic acid is +1. 
C) The hydronium concentration at the isoionic point is calculated with the equation
 
) 
D) The pH at the isoelectric point is calculated with the equation pH = ½(pK1 + pK2). 
E) For the equation
 
,F is the formal concentration of the weak acid. 
A) Isoionic pH is the pH of the pure,neutral,polyprotic acid. 
B) Isoelectric pH is the pH at which average charge of the polyprotic acid is +1. 
C) The hydronium concentration at the isoionic point is calculated with the equation
 
) 
D) The pH at the isoelectric point is calculated with the equation pH = ½(pK1 + pK2). 
E) For the equation
 
,F is the formal concentration of the weak acid. B

Question 2

For the polyprotic acid H3A,which of the equilibria below is INCORRECT?

Accepted Answer

A) A3− ⇋ HA2− + OH− Kb3 = Kw/Ka3 
B) H2A− ⇋ HA2− + H+ Ka2 = K2 
C) HA2− ⇋ A3− + H+ Ka3 = K3 
D) H3A ⇋ H2A− + H+ Ka1 = K1 
E) HA2− ⇋ H2A− + OH− Kb2 = Kw/Ka2 
A) A3− ⇋ HA2− + OH− Kb3 = Kw/Ka3 
B) H2A− ⇋ HA2− + H+ Ka2 = K2 
C) HA2− ⇋ A3− + H+ Ka3 = K3 
D) H3A ⇋ H2A− + H+ Ka1 = K1 
E) HA2− ⇋ H2A− + OH− Kb2 = Kw/Ka2 A

Question 3

Calculate the pH of a solution prepared by mixing 200.0 mL of 0.100 M NaOH with 150.0 mL of 0.200 M o×alic acid.K1 = 5.62 × 10−2,K2 = 7.24 × 10−5

Accepted Answer

pH = 1.55

Question 4

Sodium hydroxide is added to a 0.1 M solution of phenylalanine.Phenylalanine is a diprotic acid with two pKas,2.20 for the carboxylic acid group and 9.31 for the ammonium functional group.When the pH = 5.93,the principal species is____________________ and when the pH = 10.10,the principal species is____________________ .

Accepted Answer

A) H2L+;H2L+ 
B) HL;L− 
C) H2L+;L− 
D) H2L+;HL 
E) HL;HL 
A) H2L+;H2L+ 
B) HL;L− 
C) H2L+;L− 
D) H2L+;HL 
E) HL;HL

Question 5

The fractional composition diagram below is representative for diprotic weak acids.Which point INCORRECTLY indicates the principal species?

Accepted Answer

A) H2A 
B) HA− 
C) A− 
D) H2A = HA− 
E) HA− = A2− 
A) H2A 
B) HA− 
C) A− 
D) H2A = HA− 
E) HA− = A2−

Question 6

A buffer is prepared by dissolving 70 millimoles of solid NaOH in 500.0 mL of solution with a concentration of 50 mM H2A.Which of the following are NOT true for the buffer?
I After reaction there is 30 mmol HA− and 20 mmol A2− in solution.
II pH is calculated using   .
III After reaction there is 50 mmol HA− and 20 mmol NaOH in solution.
IV pH is calculated using   .
V pH = 14 - pOH where pOH is calculated from excess OH−.

Accepted Answer

A) III,IV,and V 
B) II,III,IV,and V 
C) 1,III,and IV 
D) I,II,and V 
E) I and II 
A) III,IV,and V 
B) II,III,IV,and V 
C) 1,III,and IV 
D) I,II,and V 
E) I and II

Question 7

Calculate the pH of a 0.200 M H2A− solution.K1 = 1 × 10−4,K2 = 1 × 10−8 and K3 = 1 × 10−12.

Accepted Answer

A) 4)35 
B) 6)00 
C) 8)00 
D) 8)65 
E) 10.00 
A) 4)35 
B) 6)00 
C) 8)00 
D) 8)65 
E) 10.00

Question 8

For a weak acid,the F1F1F1S1F1F1F10HA____________________ and the F1F1F1S1F1F1F10A-____________________ with increased pH.

Accepted Answer

A) increases;decreases 
B) increases;increases 
C) decreases;decreases 
D) decreases;increases 
E) is fixed ;is fixed 
A) increases;decreases 
B) increases;increases 
C) decreases;decreases 
D) decreases;increases 
E) is fixed ;is fixed

Question 9

Calculate the concentration of each species of oxalic acid in a 0.150 M solution of sodium oxalate,Na2C2O4.K1 = 5.62 × 10−2,K2 = 7.24 × 10−5

Accepted Answer

[A²⁻] = 0.15

Question 10

Malonic acid is a diprotic acid with pKs of 2.847 and 5.696.Calculate the F1F1F1S1F1F1F10 for each malonic acid species in solution at pH =3.50.

Accepted Answer

F1F1F1S1F1F1F10_H2_A = 0

Question 11

Calculate the pH to which a malonic acid solution must be adjusted to reach the isoelectric point.pK1 = 2.847 and pK2 = 5.696.

Accepted Answer

Question 12

Alanine is a diprotic amino acid with a pKa = 2.344 for the carboxylic group and a pKa = 9.868 for the ammonium group.At pH = 6.32,what is the principal species in solution?

Accepted Answer

A) H2L+ 
B) L− 
C) HL 
D) H3L2+ 
E) L2− 
A) H2L+ 
B) L− 
C) HL 
D) H3L2+ 
E) L2−

Question 13

Calculate the pH at the isoelectric point for a 0.10 M solution of the amino acid threonine.pKa1 = 2.088 and pKa2 = 9.100 for threonine.

Accepted Answer

A) 3)57 
B) 2)39 
C) 5)59 
D) 1)54 
E) 5)05 
A) 3)57 
B) 2)39 
C) 5)59 
D) 1)54 
E) 5)05

Question 14

Calculate the pH for a 0.200 M sodium L−aspartic acid solution in the H2L form.pKa1 = 1.990,pKa2 = 3.900 and pKa3 = 10.002.

Accepted Answer

Question 15

Which of the answers below is INCORRECT for diprotic acids and bases?

Accepted Answer

A) Solutions of H2A are treated as monoprotic to calculate [H+],[HA−] and [H2A]. 
B) The pH for HA− solutions is appro×imated with pH = ½(pK1 + pK2). 
C) Ka1Kb1 = Kw and Ka2Kb2 = Kw 
D) Solutions of A2− is treated as monobasic to calculate [OH−],[HA−],and [A2−]. 
E) A zwitterion is a neutral molecule with both positive and negative charges. 
A) Solutions of H2A are treated as monoprotic to calculate [H+],[HA−] and [H2A]. 
B) The pH for HA− solutions is appro×imated with pH = ½(pK1 + pK2). 
C) Ka1Kb1 = Kw and Ka2Kb2 = Kw 
D) Solutions of A2− is treated as monobasic to calculate [OH−],[HA−],and [A2−]. 
E) A zwitterion is a neutral molecule with both positive and negative charges.

Question 16

How many millimoles of NaOH or HCl must be added to 500.0 mL of 0.250 M NaO2CCO2H to prepare a pH 3.90 buffer? Assume no change in volume.pK1 = 1.250 and pK2 = 4.266.

Accepted Answer

A) 37.65 mmol NaOH 
B) 87.35 mmol HCl 
C) 124.7 mmol HCl 
D) 0)30 mmol NaOH 
E) The answer cannot be calculated from given information. 
A) 37.65 mmol NaOH 
B) 87.35 mmol HCl 
C) 124.7 mmol HCl 
D) 0)30 mmol NaOH 
E) The answer cannot be calculated from given information.

Question 17

Which of the following is TRUE for an aqueous solution of the weak acid H3A?
I H3A is acidic
II H2A− is acidic
III HA2− is amphiprotic
IV A3− is basic

Accepted Answer

A) II,III,and IV 
B) I,II,and IV 
C) I,II,and III 
D) I,III,and IV 
E) I,II,III,and IV 
A) II,III,and IV 
B) I,II,and IV 
C) I,II,and III 
D) I,III,and IV 
E) I,II,III,and IV

Question 18

Sulfurous acid is a diprotic acid with Ka1 = 1.40 × 10−2 and Ka2 = 6.73 × 10−8.Which of the statements below are FALSE?
I Kb2 = 7.14 × 10−13
II Kb1 = 1.49 × 10−7
III For 0.1 M H2SO3,[H+] = 7.61 × 10−2 for Ka1.
IV For 0.1 M NaHSO3,pH F1F1F1S1F1F1F10 4.515.

Accepted Answer

A) I,II,and IV 
B) I,II,and III 
C) I and II 
D) I,II,III,and IV 
E) II,III,and IV 
A) I,II,and IV 
B) I,II,and III 
C) I and II 
D) I,II,III,and IV 
E) II,III,and IV

Question 19

Calculate the pH of a 0.340 M NaO2CCO2H solution.pK1 = 1.250 and pK2 = 4.266.

Accepted Answer

A) 2)37 
B) 4)89 
C) 2)79 
D) 3)38 
E) −0.029 
A) 2)37 
B) 4)89 
C) 2)79 
D) 3)38 
E) −0.029

Question 20

Solid NaOH is added to 1 L of an isoleucine solution,H2L+,i.e,100 mM.When 175 mmol of NaOH is added,the principal species is____________________ .The pKa for the carboxylic acid group is 2.318 and the pKa for the ammonium group is 9.758.Assume the isoleucine solution volume does not change appreciably.

Accepted Answer

A) H2L+ 
B) L− 
C) HL 
D) H3L2+ 
E) L2− 
A) H2L+ 
B) L− 
C) HL 
D) H3L2+ 
E) L2−

Exam 11: Polyprotic Acid-Base Equilibria

Which is NOT true for isoelectric and isoionic pH?

For the polyprotic acid H3A,which of the equilibria below is INCORRECT?

Calculate the pH of a solution prepared by mixing 200.0 mL of 0.100 M NaOH with 150.0 mL of 0.200 M o×alic acid.K1 = 5.62 × 10−2,K2 = 7.24 × 10−5

The fractional composition diagram below is representative for diprotic weak acids.Which point INCORRECTLY indicates the principal species?

Calculate the pH of a 0.200 M H2A− solution.K1 = 1 × 10−4,K2 = 1 × 10−8 and K3 = 1 × 10−12.

For a weak acid,the HA____________________ and the A-____________________ with increased pH.

Calculate the concentration of each species of oxalic acid in a 0.150 M solution of sodium oxalate,Na2C2O4.K1 = 5.62 × 10−2,K2 = 7.24 × 10−5

Malonic acid is a diprotic acid with pKs of 2.847 and 5.696.Calculate the  for each malonic acid species in solution at pH =3.50.

Calculate the pH to which a malonic acid solution must be adjusted to reach the isoelectric point.pK1 = 2.847 and pK2 = 5.696.

Alanine is a diprotic amino acid with a pKa = 2.344 for the carboxylic group and a pKa = 9.868 for the ammonium group.At pH = 6.32,what is the principal species in solution?

Calculate the pH at the isoelectric point for a 0.10 M solution of the amino acid threonine.pKa1 = 2.088 and pKa2 = 9.100 for threonine.

Calculate the pH for a 0.200 M sodium L−aspartic acid solution in the H2L form.pKa1 = 1.990,pKa2 = 3.900 and pKa3 = 10.002.

Which of the answers below is INCORRECT for diprotic acids and bases?

How many millimoles of NaOH or HCl must be added to 500.0 mL of 0.250 M NaO2CCO2H to prepare a pH 3.90 buffer? Assume no change in volume.pK1 = 1.250 and pK2 = 4.266.

Which of the following is TRUE for an aqueous solution of the weak acid H3A? I H3A is acidic II H2A− is acidic III HA2− is amphiprotic IV A3− is basic

Sulfurous acid is a diprotic acid with Ka1 = 1.40 × 10−2 and Ka2 = 6.73 × 10−8.Which of the statements below are FALSE? I Kb2 = 7.14 × 10−13 II Kb1 = 1.49 × 10−7 III For 0.1 M H2SO3,[H+] = 7.61 × 10−2 for Ka1. IV For 0.1 M NaHSO3,pH  4.515.

Calculate the pH of a 0.340 M NaO2CCO2H solution.pK1 = 1.250 and pK2 = 4.266.

The Analytical Process

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Experimental Error

Statistics

Quality Assurance and Calibration Methods

Chemical Equilibrium

Let the Titrations Begin

Activity and the Systematic Treatment of Equilibrium

Monoprotic Acid-Base Equilibria

Acid-Base Titrations

Edta Titrations

Advanced Topics in Equilibrium

Fundamentals of Electrochemistry

Electrodes and Potentiometry

Redox Titrations

Electroanalytical Techniques

Fundamentals of Spectrophotometry

Applications of Spectrophotometry

Spectrophotometers

Atomic Spectroscopy

Mass Spectrometry

Introduction to Analytical Separations

Gas Chromatography

High-Performance Liquid Chromatography

Chromatographic Methods and Capillary Electrophoresis

Gravimetric and Combustion Analysis

Sample Preparation

Filters

For the polyprotic acid H₃A,which of the equilibria below is INCORRECT?

Calculate the pH of a solution prepared by mixing 200.0 mL of 0.100 M NaOH with 150.0 mL of 0.200 M o×alic acid.K₁ = 5.62 × 10⁻²,K₂ = 7.24 × 10⁻⁵

Calculate the pH of a 0.200 M H₂A⁻ solution.K₁ = 1 × 10⁻⁴,K₂ = 1 × 10⁻⁸ and K₃ = 1 × 10⁻¹².

For a weak acid,the _HA____________________ and the _A-____________________ with increased pH.

Calculate the concentration of each species of oxalic acid in a 0.150 M solution of sodium oxalate,Na₂C₂O₄.K₁ = 5.62 × 10⁻²,K₂ = 7.24 × 10⁻⁵

Calculate the pH to which a malonic acid solution must be adjusted to reach the isoelectric point.pK₁ = 2.847 and pK₂ = 5.696.

Alanine is a diprotic amino acid with a pK_a = 2.344 for the carboxylic group and a pK_a = 9.868 for the ammonium group.At pH = 6.32,what is the principal species in solution?

Calculate the pH at the isoelectric point for a 0.10 M solution of the amino acid threonine.pK_a1 = 2.088 and pK_a2 = 9.100 for threonine.

Calculate the pH for a 0.200 M sodium L−aspartic acid solution in the H₂L form.pK_a1 = 1.990,pK_a2 = 3.900 and pK_a3 = 10.002.

How many millimoles of NaOH or HCl must be added to 500.0 mL of 0.250 M NaO₂CCO₂H to prepare a pH 3.90 buffer? Assume no change in volume.pK₁ = 1.250 and pK₂ = 4.266.

Which of the following is TRUE for an aqueous solution of the weak acid H₃A? I H₃A is acidic II H₂A⁻ is acidic III HA²⁻ is amphiprotic IV A³⁻ is basic

Sulfurous acid is a diprotic acid with K_a1 = 1.40 × 10⁻² and K_a2 = 6.73 × 10⁻⁸.Which of the statements below are FALSE? I K_b2 = 7.14 × 10⁻¹³ II K_b1 = 1.49 × 10⁻⁷ III For 0.1 M H₂SO₃,[H⁺] = 7.61 × 10⁻² for K_a1. IV For 0.1 M NaHSO₃,pH  4.515.

Calculate the pH of a 0.340 M NaO₂CCO₂H solution.pK₁ = 1.250 and pK₂ = 4.266.