If you need to prepare 250.0 mL of a pH 5.00 buffer that has a total buffer concentration of acetic acid + sodium acetate of 0.050M, how many moles of each will you need to prepare the solution? Given solutions of acetic acid and sodium acetate with concentrations of 0.10M and pKa = 4.76; describe how to prepare this buffer.
For the first part, you have two equations.
base + acid = 0.05
5.00 = 4.76 + log (base(/(acid)
Solve those two simultaneously for acid and base.
Post again if you have trouble with the second part.
this was no help. at. all.
To prepare a pH 5.00 buffer solution with a total buffer concentration of acetic acid + sodium acetate of 0.050M, you need to determine the amount of acetic acid and sodium acetate required.
Step 1: Calculate the pOH of the buffer solution.
Since the pH is 5.00, the pOH can be calculated using the formula: pOH = 14 - pH = 14 - 5.00 = 9.00.
Step 2: Calculate the concentration of hydroxide ions (OH-) in the buffer solution.
From the pOH, we can find the concentration of hydroxide ions using the formula: [OH-] = 10^(-pOH) = 10^(-9.00).
Step 3: Calculate the concentration of acetic acid (CH3COOH) and sodium acetate (CH3COONa) in the buffer solution.
Using the Henderson-Hasselbalch equation: pH = pKa + log([A-]/[HA]), we can rearrange it to find the ratio of [A-]/[HA].
pH = pKa + log([A-]/[HA])
5.00 = 4.76 + log([A-]/[HA])
0.24 = log([A-]/[HA])
10^0.24 = [A-]/[HA]
1.59 = [A-]/[HA]
Since the total buffer concentration is 0.050M, we can choose any convenient value for [A-] and calculate the corresponding [HA].
Assuming [A-] = x, we have [HA] = 1.59 * x.
Step 4: Calculate the moles of acetic acid and sodium acetate needed.
Moles = concentration * volume
For acetic acid:
Moles(acetic acid) = 0.050M * 250.0mL = 0.0125 moles
For sodium acetate:
Moles(sodium acetate) = (1.59 * x) * 250.0mL = (1.59 * x * 0.2500) moles
Step 5: Balance the equation to find x (moles of sodium acetate).
The balanced equation for the dissociation of sodium acetate is:
CH3COONa ↔ CH3COO- + Na+
We know that the moles of sodium acetate must be equal to the moles of acetic acid. So, we can set up the equation:
0.0125 moles (acetic acid) = (1.59 * x * 0.2500) moles (sodium acetate)
Solving this equation will give us the value of x.
Step 6: Once you find the value of x, use it to calculate the amount of acetic acid and sodium acetate needed.
Moles(acetic acid) = 0.0125 moles
Moles(sodium acetate) = (1.59 * x * 0.2500) moles
Finally, use the molar mass of acetic acid and sodium acetate to convert moles to grams.
Note: It is crucial to accurately measure the volumes of acetic acid and sodium acetate solutions to ensure the desired concentration and pH of the buffer solution.
To prepare a pH 5.00 buffer with a total buffer concentration of acetic acid + sodium acetate of 0.050M, we need to calculate the number of moles of acetic acid and sodium acetate required.
First, we need to understand the Henderson-Hasselbalch equation, which relates the pH of a buffer solution to the pKa and the ratio of the concentrations of the conjugate acid and base in the buffer. The Henderson-Hasselbalch equation is given as:
pH = pKa + log([A-]/[HA])
Here, [A-] is the concentration of the conjugate base (sodium acetate), and [HA] is the concentration of the acid (acetic acid). Rearranging the equation, we have:
[A-]/[HA] = 10^(pH - pKa)
Given that the pH is 5.00 and the pKa is 4.76, we can calculate the ratio of [A-]/[HA]:
[A-]/[HA] = 10^(5.00 - 4.76) = 1.5849
Since the total buffer concentration is 0.050M, the sum of the concentrations of acetic acid and sodium acetate is 0.050M:
[HA] + [A-] = 0.050
Now, we can calculate the moles of acetic acid and sodium acetate needed using their respective concentrations:
[HA] = (0.050M)/(1 + [A-]/[HA]) = (0.050M)/(1 + 1.5849) = 0.0205M
and
[A-] = (0.050M) - [HA] = 0.050M - 0.0205M = 0.0295M
To convert the concentrations to moles, we need to multiply the concentrations by the volume (250.0 mL) and divide by 1000 to convert mL to L:
moles of acetic acid = (0.0205M) * (250.0mL/1000) = 0.00513 mol
moles of sodium acetate = (0.0295M) * (250.0mL/1000) = 0.00738 mol
Therefore, to prepare the pH 5.00 buffer with a total buffer concentration of 0.050M, you will need approximately 0.00513 moles of acetic acid and 0.00738 moles of sodium acetate.
To prepare the buffer, measure out 0.00513 moles of acetic acid and dissolve it in enough water to make a total volume of 250.0 mL. Then, measure out 0.00738 moles of sodium acetate and add it to the same container. Make sure to mix well to ensure complete dissolution of both compounds.