Deck 14: Advanced Topics in Equilibrium

Question 1

A student is tasked to determine the pH of a solution prepared by dissolving 20.0 mmol sodium acetate,10.0 mmol sodium oxalate (NaO₂CCO₂H),and 15.0 mmol potassium chloride in enough water to prepare 1.00 L of solution.Which of the following will simplify the algebra used to solve the problem? I.Write fractional composition equations for each acid and base in the charge balance equation.
II Substitute the fractional composition equations into the charge balance equation and enter the known values of sodium,potassium,and chloride.
III Assume the weakest acid will not contribute significantly to the pH of the solution.
IV Use a spreadsheet to perform the calculations.

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

Answer 1

I,II,and IV

Question 2

Calculate the concentration of each fumaric acid,HO₂CCHCHCO₂H,species in a 0.175 M solution at pH = 5.000.K_a1 = 9.5 × 10⁻⁴ and K_a2 = 3.3 × 10⁻⁵.

Answer 2

[H₂A] = 0.000431 M,[HA⁻] = 0.0410 M and [A²⁻] = 0.1337 M.

Question 3

The pH of a solution composed of NaO₂CCO₂H and NaCl must be determined.To get a more complete picture of the equilibrium,the mass balance equation for total oxalate is written.Which is the ONLY valid mass balance equation?

A)
B)
C)
D)
E)

Answer 3

Question 4

A solution is 0.200 M in acetic acid and 0.100 M KCl.Calculate the concentration acetic acid and acetate in solution for a pH 4.500. = 0.775, = 1, = 0.83 and K_a = 1.75 × 10⁻⁵.

Question 5

Which of the fractional composition equations is incorrectly written for the diprotic acid H₂A and the monoprotic acid HA?

A)
B)
C)
D)
E)

Question 6

The mean fraction of protons, ,bound to H₃A ranges from____________________ and (theoretical)=____________________ .

A)0 to 3;

B)1 to 3;

C)0 to 3;

D)1 to 2;

E)0 to 2;

Question 7

The pH of a solution composed of NaCH₃CO₂,NaO₂CCO₂H,and KCl must be determined.To get a more complete picture of the equilibrium,the ion-pairing equilibria are included in the calculations.Which of the following is NOT valid for ion pairing?

A)K⁺ + CH₃CO₂⁻ ⇋ KCH₃CO₂

B)Na⁺ + ^-O₂CCO₂⁻ ⇋ NaO₂CCO₂⁻

C)Na⁺ + Cl⁻ ⇋ NaCl

D)Na⁺ + CH₃CO₂⁻ ⇋ NaCH₃CO₂

E)CH₃CO₂⁻ + Cl⁻ ⇋ CH₃CO₂Cl²⁻

Question 8

The mass balance equation for the solubility of copper(II)carbonate is [Cu²⁺] = [ ]
To determine a more accurate solubility for copper(II)carbonate,additional equilibria must be written for copper(II)and carbonate in solution.Which of the mass balance equations below is the only valid charge balance equation?

A)[Cu²⁺] + [CuOH⁺] + [CuCO₃] = [

] + [

]
B)[Cu²⁺] + [CuCO₃] = [

] + [

] + [

]
C)[Cu²⁺] + [CuOH⁺] = [

] + [

] + [

] + [CuCO₃]
D)[Cu²⁺] + [CuOH⁺] = [

] + [

]+ [

]
E)[Cu²⁺] = [

] + [

]

Question 9

Calculate the pH for a buffer that is 0.10 M in NaO₂CCO₂Na and 0.50 M in NaO₂CCO₂H.K₂ = 5.42 × 10⁻⁵, = 0.333, = 0.76

A)4)209
B)4)567
C)3)965
D)4)323
E)3)908

Question 10

Which is the correct effective solubility constant expression for PbCl₂? PbCl₂ ⇋ Pb²⁺ + 2 Cl⁻

A)
B)
C)
D)
E)

Question 11

Express [Ca²⁺] in terms [H⁺] for the solubility of CaSO₄ using the equations below.Assume all activity coefficients are unity.
CaSO₄ ⇋ Ca²⁺ + K_sp = 2.40 × 10⁻⁵
Ca²⁺ + H₂O ⇋ CaOH⁺ + H⁺____________________K_a = 2.00 × 10⁻¹³
Ca²⁺ + ⇋ CaSO₄ K_ip = 229 ⇋ H⁺ + K_a2 = 1.03 × 10⁻²

Question 12

A solution is 0.120 M sodium oxalate (NaO₂CCO₂H),0.05 M chloroacetic acid (ClCH₂CO₂H)and 0.01 M KOH.Express the charge balance equation for the solution in terms of [H⁺].

Question 13

In addition to the equilibrium CaCO₃ ⇋ Ca²⁺ + CO₃^2-,additional equilibria can be written to give a more complete picture of calcium carbonate's solubility.Which of the following is NOT valid?

A)
+ H₂O ⇋

+ OH^-

B)
+ H₂O ⇋ H₂CO₃ + OH^-

C)Ca²⁺ + H₂O ⇋ CaOH⁺ + H⁺

D)Ca²⁺ +

⇋ CaCO₃

E)Ca²⁺ + H⁺ ⇋ CaH³⁺

Question 14

The rearrangement of the equilibrium constant expression to incorporate activity coefficients at the given ionic strength is the:

A)conditional equilibrium constant,K^'.
B)temporary equilibrium constant,K'.
C)combined equilibrium constant,K^'.
D)effective equilibrium constant,K^'.
E)activity equilibrium constant,K^'.

Question 15

Calculate the pH of a sulfurous acid buffer prepared from 0.010 M NaHSO₃ and 0.030 M Na₂SO₃.K_a1 = 1.39 × 10⁻² and K_a2 = 6.73 × 10⁻⁸ for sulfurous acid.
Ionic strength (,M)
Ion
0.001
0.005
0.01
0.05
0.1
Charge =  1
Activity coefficient ()
Na⁺,0.964
0.928
0.902
0.82
0.775
Charge =  2
Activity coefficient ()0.867
0.742
0.665
0.455
0.37

Question 16

The charge balance equation for the solubility of cobalt sulfide is [H⁺] + 2 [Co²⁺] = 2 [S²⁻] + [OH⁻]
To determine a more accurate solubility for cobalt sulfide,additional equilibria must be written for cobalt(II)and sulfide in solution.Which of the charge balance equations below is the only valid charge balance equation?

A)[H⁺] + 2 [Co²⁺] + [CoOH⁺] + 3 [CoH³⁺] = 2 [S²⁻] + [HS⁻] + [OH⁻]
B)[H⁺] + 2 [Co²⁺] + [CoOH⁺] = 2 [S²⁻] + [HS⁻] + [OH⁻] + 3 [SOH³⁻]
C)[H⁺] + 2 [Co²⁺] + [CoOH⁺] = 2 [S²⁻] + [HS⁻] + [OH⁻]
D)[H⁺] + 2 [Co²⁺] + 3 [CoH³⁺] = 2 [S²⁻] + [HS⁻] + [OH⁻] + 3 [SOH³⁻]
E)[H⁺] + 2 [Co²⁺] + [CoOH⁺] + 3 [CoH³⁺] = 2 [S²⁻] + [HS⁻] + [OH⁻] + 3 [SOH³⁻]

Question 17

The equilibrium constants for a diprotic acid are determined from a Bjerrum plot by:

A)fitting the theoretical curve to the experimental curve by adjusting the pH values to minimize the square of the residuals.
B)determining the slope for the upper curve which corresponds to K₁,and the slope for the lower curve which corresponds to K₂.
C)varying the pH to determine the range over which the slope of the theoretical curve is zero.Lower end of range is K₁ and upper end of range is K₂.
D)fitting the theoretical curve to the experimental curve by the method of least squares to find the values of K₁ and K₂ that minimize the square of the residuals.
E)taking the first derivative of the experimental data to determine minimums in slope.Each minimum is an equilibrium constant.

Question 18

Which is the correct effective equilibrium constant expression for the reaction of NaO₂CCO₂H with water? ⇋ + H⁺

A)

B)
C)
D)
E)

Question 19

Calculate the activity coefficient for phosphate in 0.0075 M KCl.

A)0)441
B)0)140
C)0)804
D)0)913
E)0)116

Question 20

Many ions do not have tabulated activity coefficients nor can the activity coefficient be estimated,as the ion size is now known.The Davies equation is used to estimate the activity coefficient under these conditions.Which statement(s)is(are)NOT true for the Davies equation?
I The calculated activity coefficient is independent of the ion's size.
II The ion's charge,the solutions ionic strength and the ion size are required to calculate the activity coefficient.
III The Davies equation can be used up to ~ 0.5 M ionic strength.
IV The calculated activity coefficient is no more accurate than guessing the ion size to determine the activity coefficient.

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