a buffer is to be prepared by adding solid sodium acetate to 0.10M CH3COOH. Which othe following concentrations of sodium acetate will produce the most effective buffer?
A. 3.0M CH3COONa
B 2.5M CH3COONa
C 2.0M CH3COONa
D 1.5M CH3COONa
E .30M CH3COONa
HELP
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Buffers are most effective when the pKa is in the range of desired pH; and that means base/acid = 1
So you want to pick the NaC2H3O2 concn that gives the value closest to b/a = 1.
E 0.30
To determine which concentration of sodium acetate will produce the most effective buffer, we need to consider the Henderson-Hasselbalch equation for buffer solutions.
The Henderson-Hasselbalch equation is given by:
pH = pKa + log([A-]/[HA])
Where:
pH is the desired pH of the buffer
pKa is the dissociation constant of the weak acid (CH3COOH)
[A-] is the concentration of the conjugate base (CH3COO-) of the weak acid
[HA] is the concentration of the weak acid (CH3COOH)
In this case, the weak acid is CH3COOH, and we want to prepare a buffer by adding solid sodium acetate (CH3COONa). The sodium acetate will dissociate in water to produce the conjugate base (CH3COO-) and sodium ions (Na+).
To determine the most effective buffer, we need to calculate the pH of the buffer using the Henderson-Hasselbalch equation for each concentration of sodium acetate.
Let's calculate the pH for each option:
A. 3.0M CH3COONa:
Since this concentration is not given, we cannot calculate the pH.
B. 2.5M CH3COONa:
Similarly, this concentration is not given, so we cannot calculate the pH.
C. 2.0M CH3COONa:
Again, this is not a given concentration, so we cannot calculate the pH.
D. 1.5M CH3COONa:
Unfortunately, this concentration is also not given, so we cannot calculate the pH.
E. 0.30M CH3COONa:
This concentration is given, so we can proceed to calculate the pH.
We need to find the pKa of acetic acid (CH3COOH) first. The pKa of acetic acid is approximately 4.76.
Substituting the values into the Henderson-Hasselbalch equation, we have:
pH = 4.76 + log([0.30M]/[0.10M])
pH = 4.76 + log(3.0)
pH = 4.76 + 0.48
pH ≈ 5.24
Therefore, option E with a concentration of 0.30M CH3COONa will produce the most effective buffer with a pH of approximately 5.24.
To determine which concentration of sodium acetate will produce the most effective buffer with 0.10M CH3COOH, we need to consider the principles of buffer solutions.
A buffer solution is a solution that resists changes in pH when small amounts of acid or base are added. It consists of a weak acid and its conjugate base (or a weak base and its conjugate acid) in roughly equal amounts.
In this case, CH3COOH (acetic acid) is the weak acid, and CH3COONa (sodium acetate) is its conjugate base.
The effectiveness of a buffer solution depends on the ratio of the concentrations of the weak acid and its conjugate base. The ideal ratio is 1:1 (equal concentrations), which allows the buffer to efficiently neutralize added acid or base.
Therefore, to determine the most effective buffer, we need to find the concentration of sodium acetate that is closest to 0.10M (the concentration of acetic acid).
Let's compare the given concentrations of sodium acetate:
A. 3.0M CH3COONa: This concentration is significantly higher than the desired concentration of acetic acid (0.10M). The buffer solution would be too basic, and it may not effectively resist changes in pH. Therefore, this concentration is not the most effective buffer.
B. 2.5M CH3COONa: This concentration is still higher than the desired concentration of acetic acid but is closer than 3.0M. The buffer solution would be slightly too basic, but it should still effectively resist changes in pH. This concentration may be a good option, but let's continue checking the others.
C. 2.0M CH3COONa: This concentration is much closer to the desired concentration of acetic acid (0.10M). The buffer solution would be nearly ideal and should effectively resist changes in pH. This concentration is a strong contender for the most effective buffer.
D. 1.5M CH3COONa: This concentration is lower than the desired concentration of acetic acid. The buffer solution would be slightly too acidic, and it may not effectively resist changes in pH. Therefore, this concentration is not the most effective buffer.
E. 0.30M CH3COONa: This concentration is significantly lower than the desired concentration of acetic acid. The buffer solution would be too acidic, and it may not effectively resist changes in pH. Therefore, this concentration is not the most effective buffer.
Based on the analysis, the most effective buffer would have a concentration of 2.0M CH3COONa (Option C).