Thank you for visiting You need to make 250 0 mL of a buffer with a pH of 4 10 In the chemical storage room you found formic acid. This page is designed to guide you through key points and clear explanations related to the topic at hand. We aim to make your learning experience smooth, insightful, and informative. Dive in and discover the answers you're looking for!
Answer :
The student needs to calculate the moles of formic acid required to create a buffer solution with pH 4.10 using the Henderson-Hasselbalch equation, after converting mass of sodium formate to moles. The calculation gives 0.231 moles of formic acid, which should then be appropriately adjusted to the volume of the buffer solution being prepared.
The main answer to the question of how many moles of formic acid is required to make 250.0 mL of a buffer with a pH of 4.10 involves using the Henderson-Hasselbalch equation, which relates pH, pKa, and the ratio of the concentrations of the conjugate base (A-) to the conjugate acid (HA). The formula is given by:
\( pH = pKa + \log(\frac{[A-]}{[HA]}) \)
In this case, the student has formic acid (HA) with a pKa of 3.74 and sodium formate (NaCHO2, the conjugate base, A-) available to make the buffer. They were also given the mass of sodium formate already present. To find the number of moles of formic acid needed, we can rearrange the equation to solve for [HA].
First, convert the mass of sodium formate to moles:
\( 35.9 \text{ grams NaCHO2} \times \frac{1 \text{ mole NaCHO2}}{68.01 \text{ grams NaCHO2}} = 0.528 \text{ moles NaCHO2} \)
This number of moles of formate corresponds to the [A-] in our equation.
Using the Henderson-Hasselbalch equation:
\( 4.10 = 3.74 + \log(\frac{0.528}{[HA]}) \)
From here, we can isolate [HA] and find the number of moles of formic acid needed:
\( [HA] = 0.528 \text{ moles} / 10^{(4.10-3.74)} \)
Finally, calculate the exact number of moles of formic acid:
\( [HA] = 0.528 \text{ moles} / 10^{0.36} \)
\( [HA] = 0.528 \text{ moles} / 2.29 \)
\( [HA] = 0.231 \text{ moles} \)
Since the buffer is to be prepared in 250.0 mL, the proportion of [HA] that corresponds to this volume must be calculated. The resulting moles of formic acid would be the amount needed for the 250.0 mL buffer solution.
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