Calculate the relative concentrations of NaH2PO4 and H3PO4 required, giving a solution, which buffers at pH 2.6. (The pKa1 for H3PO4 is 2.1).
The Henderson-Hasselbalch equation is
pH = pKa + log [(base)/(acid)]
You have pH, you can calculate pKa, substitute and solve for (base)/(acid)
Post your work if you get stuck.
To calculate the relative concentrations of NaH2PO4 and H3PO4 required for a buffer solution at pH 2.6, we need to use the Henderson-Hasselbalch equation:
pH = pKa + log ([A-]/[HA])
Where:
pH = desired pH (2.6)
pKa = -log(Ka) = -log(10^-2.1) = 2.1
[A-] = concentration of the conjugate base (in this case, H2PO4-)
[HA] = concentration of the acid (in this case, H3PO4)
First, calculate the ratio of [A-]/[HA] using the Henderson-Hasselbalch equation:
2.6 = 2.1 + log([A-]/[HA])
Rearrange the formula:
log([A-]/[HA]) = 2.6 - 2.1
log([A-]/[HA]) = 0.5
Taking antilog of both sides:
[A-]/[HA] = antilog(0.5) = 3.16
Since we want to calculate the relative concentrations, we can assume the concentration of one species and calculate the concentration of the other. Let's assume the concentration of H3PO4 ([HA]).
Assume [HA] = 1 (you can choose any unit for concentration, like M or mol/L).
[A-]/[HA] = 3.16
[A-]/1 = 3.16
Therefore, the concentration of H2PO4- ([A-]) is 3.16.
So, the relative concentrations of NaH2PO4 and H3PO4 required for a buffer at pH 2.6 is approximately 3.16:1.
To calculate the relative concentrations of NaH2PO4 and H3PO4 required to create a buffer solution at pH 2.6, we need to use the Henderson-Hasselbalch equation:
pH = pKa + log([A-]/[HA])
Where pH is the desired pH of the buffer solution, pKa is the acid dissociation constant, [A-] is the concentration of the conjugate base, and [HA] is the concentration of the acid.
In this case, we want to create a buffer at pH 2.6, and the pKa1 of H3PO4 is given as 2.1. Therefore, we can plug these values into the equation:
2.6 = 2.1 + log([A-]/[HA])
Now, we need to solve for the ratio of [A-] to [HA] in order to determine the relative concentrations.
To do this, we can rearrange the equation:
log([A-]/[HA]) = 2.6 - 2.1
log([A-]/[HA]) = 0.5
Next, we can convert the logarithmic equation into an exponential equation:
10^(log([A-]/[HA])) = 10^0.5
[A-]/[HA] = 10^0.5
Finally, we can solve for the concentrations by assuming a value for [HA] and finding the corresponding value for [A-]. Let's assume [HA] = 1 M. Therefore,
[A-] = 10^0.5 * [HA]
The concentration of NaH2PO4 will be [A-], and the concentration of H3PO4 will be [HA]. However, it's important to note that these concentrations are relative, and you will need to choose appropriate absolute concentrations based on your experimental requirements.