What is the composition of 0.1M sodium acetate buffer,pH 5.00?
To determine the composition of a buffer solution, such as the 0.1M sodium acetate buffer at pH 5.00, you need to know the pKa value of the acid in the buffer system. In this case, the acid is acetic acid (CH3COOH), and its pKa value is 4.74.
The Henderson-Hasselbalch equation, which relates the pH, pKa, and the concentration of the acid and its conjugate base, can be used to determine the composition of a buffer solution. The Henderson-Hasselbalch equation is:
pH = pKa + log([A-]/[HA])
Where pH is the desired pH, pKa is the acid dissociation constant, [A-] is the concentration of the conjugate base (acetate ion, CH3COO-), and [HA] is the concentration of the acid (acetic acid, CH3COOH).
In this case, pH = 5.00 and pKa = 4.74. We want to find the concentrations of [A-] (acetate ion) and [HA] (acetic acid) in the buffer.
Rearranging the Henderson-Hasselbalch equation, we get:
log([A-]/[HA]) = pH - pKa
Substituting the given values, we can solve for the ratio of [A-]/[HA]:
log([A-]/[HA]) = 5.00 - 4.74 = 0.26
Using logarithmic properties, we can convert this equation to exponential form:
[A-]/[HA] = 10^0.26
[A-]/[HA] = 1.778
Therefore, the ratio of acetate ion ([A-]) to acetic acid ([HA]) in the buffer is approximately 1.778.
Now that we have the ratio, we can choose any value for the concentration of [A-] or [HA]. Let's assume the concentration of acetic acid ([HA]) is 1M.
[A-] = 1.778 * [HA]
[A-] = 1.778 * 1M
[A-] = 1.778M
Therefore, the concentration of acetate ion ([A-]) in the 0.1M sodium acetate buffer at pH 5.00 is approximately 1.778M, and the concentration of acetic acid ([HA]) is 1.0M.
To summarize, the composition of the buffer is approximately 0.1M sodium acetate (CH3COONa) and 1.0M acetic acid (CH3COOH).