Open Question
A buffer is created by combining 150.0 mL of 0.25 M HCHO2 with 75.0 mL of 0.20 M NaOH. Determine the pH of the buffer.
Ch.17 - Aqueous Ionic Equilibrium
Chapter 17, Problem 118
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?
Verified step by step guidance1
Identify the components of the buffer solution: HCHO2 (formic acid) and NaCHO2 (sodium formate).
Use the Henderson-Hasselbalch equation: \( \text{pH} = \text{pK}_a + \log \left( \frac{[\text{A}^-]}{[\text{HA}]} \right) \), where \( \text{A}^- \) is the conjugate base (formate ion) and \( \text{HA} \) is the weak acid (formic acid).
Calculate the initial pH of the buffer using the given concentrations and the \( \text{pK}_a \) of formic acid (3.74).
Determine whether the pH needs to be increased or decreased to reach 4.10. If the pH needs to be increased, add NaOH; if it needs to be decreased, add HCl.
Calculate the amount of NaOH or HCl needed to adjust the pH to 4.10 using the buffer capacity and the change in moles of \( \text{A}^- \) or \( \text{HA} \) required. Convert this amount to mass using the molar mass of the reagent.
Related Practice
Open Question
A buffer is created by combining 3.55 g of NH3 with 4.78 g of HCl and diluting to a total volume of 750.0 mL. Determine the pH of the buffer.
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?
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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?
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Open Question
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?
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?
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