Skip to main content
Pearson+ LogoPearson+ Logo
Ch.17 - Aqueous Ionic Equilibrium
All textbooksTro 4th EditionCh.17 - Aqueous Ionic EquilibriumProblem 121
Previous problem
Next problem
Chapter 17, Problem 121

A 0.25-mol sample of a weak acid with an unknown pKa was combined with 10.0 mL of 3.00 M KOH, and the resulting solution was diluted to 1.500 L. The measured pH of the solution was 3.85. What is the pKa of the weak acid?

Verified step by step guidance
1
Calculate the moles of KOH added using the formula: \( \text{moles of KOH} = \text{volume (L)} \times \text{concentration (M)} \).
Determine the moles of the weak acid that reacted with KOH by subtracting the moles of KOH from the initial moles of the weak acid.
Calculate the concentration of the conjugate base formed by dividing the moles of the conjugate base by the total volume of the solution (1.500 L).
Use the Henderson-Hasselbalch equation: \( \text{pH} = \text{pKa} + \log \left( \frac{[\text{A}^-]}{[\text{HA}]} \right) \) to solve for pKa, where \([\text{A}^-]\) is the concentration of the conjugate base and \([\text{HA}]\) is the concentration of the weak acid.
Rearrange the Henderson-Hasselbalch equation to solve for pKa: \( \text{pKa} = \text{pH} - \log \left( \frac{[\text{A}^-]}{[\text{HA}]} \right) \).
Previous problem
Next problem
Related Practice
Textbook Question

A 1.0-L buffer solution initially contains 0.25 mol of NH3 and 0.25 mol of NH4Cl. In order to adjust the buffer pH to 8.75, should you add NaOH or HCl to the buffer mixture? What mass of the correct reagent should you add?

2806
views
Open Question
To adjust the pH of a 250.0-mL buffer solution initially containing 0.025 mol of HCHO2 and 0.025 mol of NaCHO2 to 4.10, should you add NaOH or HCl, and what mass of the correct reagent should you add?
Textbook Question

In analytical chemistry, bases used for titrations must often be standardized; that is, their concentration must be precisely determined. Standardization of sodium hydroxide solutions can be accomplished by titrating potassium hydrogen phthalate (KHC8H4O4), also known as KHP, with the NaOH solution to be standardized. b. The titration of 0.5527 g of KHP required 25.87 mL of an NaOH solution to reach the equivalence point. What is the concentration of the NaOH solution?

868
views
Textbook Question

A 5.55-g sample of a weak acid with Ka = 1.3⨉10-4 was combined with 5.00 mL of 6.00 M NaOH, and the resulting solution was diluted to 750.0 mL. The measured pH of the solution was 4.25. What is the molar mass of the weak acid?

996
views
2
comments
Open Question
From the data given—where a 0.552-g sample of ascorbic acid (vitamin C) is dissolved in water to a total volume of 20.0 mL and titrated with 0.1103 M KOH, the equivalence point occurred at 28.42 mL, and the pH of the solution at 10.0 mL of added base was 3.72—determine the molar mass and dissociation constant (Ka) for vitamin C.
Open Question
Calculate the pH at the beginning of the titration, at the equivalence point, at one-half of the equivalence point, and at 5.0 mL beyond the equivalence point to sketch the titration curve from Problem 123. Then, choose a suitable indicator for this titration from Table 17.1.