Exam 14: Advanced Topics in Equilibrium

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?

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

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 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.

Calculate the activity coefficient for phosphate in 0.0075 M KCl.

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

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

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

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⁺].

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

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.

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

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?

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.

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

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?

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?

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

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?

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