A buffer consists of 0.14 M KHCO3 and 0.61 M K2CO3. Carbonic acid is a dirpotic acid with Ka1= 4.5*10^-7 and Ka2= 4.7*10^-11.

a) which Ka value is more important to this buffer
b) what is the buffer pH?

Look at the constituents of k1 and k2 and choose the one that matches the reaction.

You have HCO3^- and CO3^2- in the problem.
Write k1 and k2 expressions. Then determine which one has HCO3^- and CO3^2- in it.

To determine which Ka value is more important to the buffer, we need to compare the concentrations of the reacting species in the buffer solution.

For carbonic acid (H2CO3), it will dissociate to form the HCO3- ion and release a proton (H+). This is based on the equilibrium reaction: H2CO3 ⇌ HCO3- + H+.

a) To calculate the concentration of carbonic acid (H2CO3), we first need to know the concentrations of its conjugate base (HCO3-) and the base ion (CO32-). In this case, the concentrations given are 0.14 M for KHCO3 and 0.61 M for K2CO3.

Since KHCO3 is a strong electrolyte and dissociates completely into its ions, the concentration of HCO3- will be equal to that of KHCO3, i.e., 0.14 M.

For K2CO3, it will dissociate to form 2 K+ ions and one CO32- ion. Hence, the concentration of the CO32- ion will be half of the K2CO3 concentration, i.e., 0.305 M.

Now, let's compare the concentrations of the HCO3- and the CO32- ions:
[HCO3-] = 0.14 M
[CO32-] = 0.305 M

b) The buffer pH can be calculated using the Henderson-Hasselbalch equation:
pH = pKa + log([A-]/[HA])

In this case, HCO3- acts as the conjugate base (A-) and H2CO3 acts as the acid (HA). The pKa value that is more relevant to the buffer will determine the pH.

To determine the important Ka value, we need to compare the concentrations of HCO3- and H2CO3. From the previous calculation, we found that [HCO3-] = 0.14 M.

The concentration of H2CO3 can be calculated using the expression:
[H2CO3] = [CO32-] * (Ka1/Ka2)

Given the Ka1 and Ka2 values, [CO32-] = 0.305 M, and by solving the expression:
[H2CO3] = 0.305 M * (4.5*10^-7/4.7*10^-11)

By calculating this expression, we find that [H2CO3] = 2.933 M * 10^-4.

Now, we can compare the concentrations:
[HCO3-] = 0.14 M
[H2CO3] = 2.933 M * 10^-4

Since the concentration of H2CO3 is significantly less than that of HCO3-, we can conclude that the first dissociation step (Ka1) of carbonic acid is more important for this buffer.

To calculate the buffer pH, we can substitute the values into the Henderson-Hasselbalch equation:
pH = pKa + log([A-]/[HA])
pH = pKa1 + log([HCO3-]/[H2CO3])

Using the given Ka1 value of 4.5*10^-7 (which is relevant for this buffer), and the concentrations we determined earlier:
pH = log(0.14/2.933 M * 10^-4)

Calculate this expression to find the buffer pH.