What is te component concentration ratio, [NO2-]/[HNO2], of a buffer that has a pH of 2.42 (Ka of HNO2=7.1 x 10^-4)?
0.186
Substitute into the Henderson-Hasselbalch equation.
To find the component concentration ratio, [NO2-]/[HNO2], of a buffer, we need to consider the Henderson-Hasselbalch equation, which relates the pH of a buffer solution to the ratio of its component concentrations.
The Henderson-Hasselbalch equation is given by:
pH = pKa + log([A-]/[HA])
Where:
pH is the given pH value of the buffer.
pKa is the negative logarithm (base 10) of the acid dissociation constant of the acid in the buffer.
[A-] is the concentration of the conjugate base.
[HA] is the concentration of the acid.
In this case, the acid is HNO2, and the conjugate base is NO2-. We are given the pH as 2.42, and the Ka of HNO2 as 7.1 x 10^-4.
First, let's calculate the pKa value by taking the negative logarithm of the given Ka:
pKa = -log(7.1 x 10^-4)
pKa ≈ 3.15
Now, we can rearrange the Henderson-Hasselbalch equation to solve for the component concentration ratio [NO2-]/[HNO2]:
pH = pKa + log([NO2-]/[HNO2])
2.42 = 3.15 + log([NO2-]/[HNO2])
Next, we can isolate the logarithmic term:
log([NO2-]/[HNO2]) = 2.42 - 3.15
log([NO2-]/[HNO2]) ≈ -0.73
Now, we can eliminate the logarithm by taking the antilog of both sides of the equation:
[NO2-]/[HNO2] = antilog(-0.73)
[NO2-]/[HNO2] ≈ 0.183
Therefore, the component concentration ratio, [NO2-]/[HNO2], of the given buffer with a pH of 2.42 is approximately 0.183.