1. It is found that the equilibrium concentration of the undissociated form (HA) of a weak...
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1. It is found that the equilibrium concentration of the undissociated form (HA) of a weak monoprotic acid, in an aqueous solution of pH-3, is 9.398x104 mol/L. It is also known that an equal amount of the same acid at pH-6 dissociates to produce an equilibrium concentration of its conjugate base (A) of 8.649×10 mol/L. Find the equilibrium constant of the weak acid. Show all calculations. Assume a closed system. 2. The conversion of chromate to dichromate in an aqueous solution can be expressed by the following equilibrium equation: 2CrO2 + 2H+ Cr₂0² + H₂O a) Use data from thermodynamic tables to obtain the value of the equilibrium constant for the transformation of chromate to dichromate at 25°C. If the equilibrium chromate concentration of an aqueous solution is 1.2×10-³M at a pH=5, determine its dichromate concentration. Neglect ionic strength effects. b) Approximately 750 mg/L of NaCl are added to the solution described in part a). Determine the concentration of chromate and dichromate at the equilibrium established after the salt addition. Assume that the pH remains constant during the process. Does salt addition favor the formation of dichromate? 3. [30] Buffer solutions are typically prepared by mixing a weak acid with its conjugate base. A buffer solution is prepared by adding 0.55 moles sodium nitrite (NaNO₂) and 0.85 moles nitrous acid (HNO₂) in 1 liter of water. The equilibrium constant of the dissociation of nitrous acid K₂=4.27×104. Assume complete dissociation of the salt. a) Determine the final pH of the buffer solution using the analytical method developed in class for monoprotic acids. b) Use the Henderson-Hasselbalch equation, as a quick approximation, to compute the final pH of the solution. What is the percent error for this approximation? 1. It is found that the equilibrium concentration of the undissociated form (HA) of a weak monoprotic acid, in an aqueous solution of pH-3, is 9.398x104 mol/L. It is also known that an equal amount of the same acid at pH-6 dissociates to produce an equilibrium concentration of its conjugate base (A) of 8.649×10 mol/L. Find the equilibrium constant of the weak acid. Show all calculations. Assume a closed system. 2. The conversion of chromate to dichromate in an aqueous solution can be expressed by the following equilibrium equation: 2CrO2 + 2H+ Cr₂0² + H₂O a) Use data from thermodynamic tables to obtain the value of the equilibrium constant for the transformation of chromate to dichromate at 25°C. If the equilibrium chromate concentration of an aqueous solution is 1.2×10-³M at a pH=5, determine its dichromate concentration. Neglect ionic strength effects. b) Approximately 750 mg/L of NaCl are added to the solution described in part a). Determine the concentration of chromate and dichromate at the equilibrium established after the salt addition. Assume that the pH remains constant during the process. Does salt addition favor the formation of dichromate? 3. [30] Buffer solutions are typically prepared by mixing a weak acid with its conjugate base. A buffer solution is prepared by adding 0.55 moles sodium nitrite (NaNO₂) and 0.85 moles nitrous acid (HNO₂) in 1 liter of water. The equilibrium constant of the dissociation of nitrous acid K₂=4.27×104. Assume complete dissociation of the salt. a) Determine the final pH of the buffer solution using the analytical method developed in class for monoprotic acids. b) Use the Henderson-Hasselbalch equation, as a quick approximation, to compute the final pH of the solution. What is the percent error for this approximation?
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1 To find the equilibrium constant Ka for the weak acid we can use the HendersonHasselbalch equation pH pKa logAHA Given pH 3 A 864910 molL HA 939810 ... View the full answer
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Financial Reporting and Analysis
ISBN: 978-0078025679
6th edition
Authors: Flawrence Revsine, Daniel Collins, Bruce, Mittelstaedt, Leon
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