To prepare an effective buffer in a PH range less than 7 ,it is advisable to select a weak acid-conjugate base pair in which the pK(a) of the weak acid equals the desired PH (+-)1
Over what PH range is the acetic acid-acetate ion buffer most effective ?K(HC2H3O2)=1.8x10^-5
thank for helps =]
If Ka = 1.8E-5, then pKa = 4.74 so the range is 3.74 to 5.74
To determine the pH range in which an acetic acid-acetate ion buffer is most effective, we need to consider the pKa value of the weak acid (acetic acid).
The Henderson-Hasselbalch equation is commonly used to determine the pH of a buffer solution, which is given by:
pH = pKa + log([A-]/[HA])
In this equation, [A-] represents the concentration of the conjugate base (acetate ion) and [HA] represents the concentration of the weak acid (acetic acid).
To calculate the pH range in which the buffer is most effective, we need to consider the relationship between the pH and the ratio [A-]/[HA]. This ratio is important because it determines the effectiveness of the buffer in maintaining a relatively constant pH.
Since the pH range less than 7 is specified in your question, we need to find the range of [A-]/[HA] values that corresponds to pH values less than 7.
First, let's calculate the pH at which the buffer solution is most effective (pKa + 1). Using the given pKa value of acetic acid (1.8x10^-5), we can calculate the pH:
pH = pKa + 1 = -log10(1.8x10^-5) + 1 ≈ 4.75
This means that the buffer solution is most effective around pH 4.75.
Now, let's consider the pH range in which the buffer works within the specified pH range (less than 7). To do this, we need to look at the pH range in which the ratio [A-]/[HA] is approximately 10. This is obtained by considering the logarithmic relationship in the Henderson-Hasselbalch equation.
To determine the pH range, we can rearrange the Henderson-Hasselbalch equation and solve for the ratio [A-]/[HA]:
[A-]/[HA] = 10^(pH - pKa)
Now, let's calculate the ratio for pH = 6, which is the upper limit of the specified pH range:
[A-]/[HA] = 10^(6 - 1.8x10^-5) ≈ 3981.07
Next, let's calculate the ratio for pH = 7, which is just outside the specified pH range:
[A-]/[HA] = 10^(7 - 1.8x10^-5) ≈ 7943.28
Therefore, the acetic acid-acetate ion buffer is most effective within the pH range approximately 4.75 to 6.