What is the ratio of KC2H3O2 and HC2H3O2 in a buffer with a pH of 5.25? Ka = 1.8 x10-5?
Use the Henderson-Hasselbalch equation.
I understand that is the equation but I can not figure out how I get the numbers. I know the equation is
ph= pka + log [salt]/[acid]
I know pka is -logKa but I do not know how to get the numbers for the [salt] or the [acid] to divide. I have an extremely
HORRENDOUSLY bad college professor who pretty much says he is trying to weed out the potentially bad nurses that cannot do these things.
To determine the ratio of KC2H3O2 and HC2H3O2 in a buffer, we need to use the Henderson-Hasselbalch equation:
pH = pKa + log([A-]/[HA])
Where:
pH is the given pH of the buffer
pKa is the acid dissociation constant
[A-] is the concentration of the conjugate base (KC2H3O2)
[HA] is the concentration of the weak acid (HC2H3O2)
In this case, we are given the pH (5.25) and the pKa (1.8 x 10^-5). So let's substitute these values into the Henderson-Hasselbalch equation:
5.25 = -log(1.8 x 10^-5) + log([A-]/[HA])
Let's simplify the equation:
5.25 + log([HA]/[A-]) = log(1.8 x 10^-5)
Next, we can convert the logarithmic equation to an exponential equation:
10^(5.25 + log([HA]/[A-])) = 1.8 x 10^-5
Now, let's isolate the ratio [HA]/[A-]:
[HA]/[A-] = 10^(5.25) / 1.8 x 10^-5
[HA]/[A-] = (10^5.25) / (1.8 x 10^-5)
[HA]/[A-] ≈ 177.827
Therefore, in the given buffer system, the ratio of KC2H3O2 to HC2H3O2 is approximately 177.827.