What volumes of 0.53 M HNO2 and 0.46 M NaNO2 must be mixed to prepare 1.00 L of a solution buffered at pH = 3.55?
HNO2
Use the Henderson-Hasselbalch equation.
pH = pKa + log (base/acid)
You must look up Ka and substitute pKa.
To prepare a buffer solution, you need to consider the Henderson-Hasselbalch equation:
pH = pKa + log ([A-]/[HA])
In this case, HNO2 acts as a weak acid (HA) and NaNO2 as its conjugate base (A-). The pKa value for HNO2 can be found in a reference table, which is 3.15 for this compound.
First, calculate the concentration ratio ([A-]/[HA]) using the given pH value:
pH = pKa + log ([A-]/[HA])
3.55 = 3.15 + log ([A-]/[HA])
Simplifying the equation, you get:
0.4 = log ([A-]/[HA])
10^0.4 = [A-]/[HA]
2.5119 = [A-]/[HA]
The ratio of [A-] to [HA] in a buffer solution is given by:
[A-]/[HA] = (V[A-])/(V[HA])
where V[A-] and V[HA] represent the volumes of NaNO2 and HNO2, respectively.
Since the total volume of the buffer solution is 1.00 L, you can express this in terms of V[A-]:
V[A-] = (2.5119)/(1 + 2.5119) * 1.00
V[A-] = 0.714 L
The volume of HNO2 can be calculated by subtracting the volume of NaNO2 from the total volume:
V[HA] = 1.00 - 0.714
V[HA] = 0.286 L
Therefore, to prepare a 1.00 L buffer solution with a pH of 3.55, you need to mix 0.714 L of 0.46 M NaNO2 and 0.286 L of 0.53 M HNO2.
228mL
452mL