Open Question
A weak monoprotic acid is titrated with 0.100 M NaOH. It requires 50.0 mL of the NaOH solution to reach the equivalence point. After 25.0 mL of base is added, the pH of the solution is 3.62. Estimate the pKa of the weak acid.
Ch.17 - Additional Aspects of Aqueous Equilibria
Chapter 17, Problem 96
How many microliters of 1.000 M NaOH solution must be added to 25.00 mL of a 0.1000 M solution of lactic acid CH3CH(OH)COOH or HC3H5O3 to produce a buffer with pH = 3.75?
Verified step by step guidance1
Identify the components of the buffer system: lactic acid (HC3H5O3) and its conjugate base (C3H5O3^-).
Use the Henderson-Hasselbalch equation: \( \text{pH} = \text{pK}_a + \log \left( \frac{[\text{A}^-]}{[\text{HA}]} \right) \) to relate pH, pKa, and the ratio of concentrations of the conjugate base and acid.
Find the \( \text{pK}_a \) of lactic acid, which is approximately 3.86.
Rearrange the Henderson-Hasselbalch equation to solve for the ratio \( \frac{[\text{A}^-]}{[\text{HA}]} \) using the given pH of 3.75.
Calculate the moles of lactic acid initially present and use stoichiometry to determine the moles of NaOH needed to achieve the desired ratio, then convert this to volume in microliters.
Related Practice
Open Question
What is the pH of a solution made by mixing 0.30 mol NaOH, 0.25 mol Na2HPO4, and 0.20 mol H3PO4 with water and diluting to 1.00 L?
Textbook Question
Suppose you want to do a physiological experiment that calls for a pH 6.50 buffer. You find that the organism with which you are working is not sensitive to the weak acid H2A 1Ka1 = 2 * 10-2; Ka2 = 5.0 * 10-72 or its sodium salts. You have available a 1.0 M solution of this acid and a 1.0 M solution of NaOH. How much of the NaOH solution should be added to 1.0 L of the acid to give a buffer at pH 6.50? (Ignore any volume change.)
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Textbook Question
Lead(II) carbonate, PbCO3, is one of the components of the passivating layer that forms inside lead pipes. (d) The EPA threshold for acceptable levels of lead ions in water is 15 ppb. Does a saturated solution of lead(II) carbonate produce a solution that exceeds the EPA limit?
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Textbook Question
For each pair of compounds, use Ksp values to determine which has the greater molar solubility: (b) PbCO3 or BaCrO4.
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Textbook Question
The solubility of CaCO3 is pH dependent. (b) Use the Kb expression for the CO32 - ion to determine the equilibrium constant for the reaction CaCO31s2 + H2O1l2 ΔCa2 + 1aq2 + HCO3-1aq2 + OH-1aq2
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