1- Determine the [OH-] and pH of a solution that is .250 M in HCO-3

2- Calculate the [H3O+] and pH of each polyprotic acid solution:
a) .125 M H2CO3
b) .125 M H3C6H5O7

To determine the [OH-] and pH of a solution, we first need to understand the concept of dissociation of the given compound.

1. For HCO-3:
HCO-3 is the bicarbonate ion, and it can undergo a reaction with water to release hydroxide ions (OH-) and form carbonic acid (H2CO3). The equilibrium equation for this reaction is:

HCO-3 + H2O ⇌ OH- + H2CO3

To determine the [OH-] and pH, we need to consider the dissociation constant (Ka) of carbonic acid (H2CO3), which is a weak acid. The equation for the dissociation of H2CO3 is:

H2CO3 ⇌ H+ + HCO-3

The [OH-] concentration will depend on the concentration of H+ ions in the solution. Since H2CO3 is a weak acid, we can assume that the dissociation is minimal and neglect the contribution of H2CO3 to the [H+] concentration.

Therefore, since the initial concentration of HCO-3 is given as 0.250 M, we can consider the [OH-] concentration to be equal to the [H+] concentration.

So, [OH-] = [H+] = 0.250 M

To determine the pH, we can use the formula:

pH = -log[H+]

Substituting the [H+] concentration, we get:

pH = -log(0.250) = 0.60

Therefore, the [OH-] concentration is 0.250 M, and the pH of the solution is 0.60.

2. For polyprotic acids:
Polyprotic acids, such as H2CO3 (carbonic acid) and H3C6H5O7 (citric acid), have multiple acidic protons that can dissociate successively. However, their dissociation constants can differ, resulting in a stepwise dissociation. We will calculate the [H3O+] and pH for both cases:

a) H2CO3:
H2CO3 is a diprotic acid, which means it can lose two protons successively. The dissociation reactions are as follows:

H2CO3 ⇌ H+ + HCO-3

HCO-3 ⇌ H+ + CO3-2

Since the concentration of H2CO3 is given as 0.125 M, we can assume negligible dissociation of the second proton (HCO-3 to CO3-2). So, we consider only the first dissociation:

[H3O+] = [H+] = 0.125 M

Using the formula pH = -log[H+], we get:

pH = -log(0.125) = 0.90

Thus, the [H3O+] concentration is 0.125 M, and the pH of the solution is 0.90.

b) H3C6H5O7:
H3C6H5O7 is a polyprotic acid with three acidic protons. The dissociation reactions are relatively complex, involving multiple equilibrium equations. To accurately calculate the [H3O+] and pH, we require additional information: the equilibrium constants (Ka) for each dissociation step. These constants depend on temperature and would need to be provided.

Please provide the Ka values for H3C6H5O7, or any additional information, so that we can calculate the [H3O+] and pH for this case.