Oxalic acid & phosphoric acid are polyprotic acid. For both acids, provide the equilibrium reactions showing all of the dissociation steps and the expressions for each acid dissociation constans.
To determine the equilibrium reactions and expressions for dissociation constants for the polyprotic acids, oxalic acid (H2C2O4) and phosphoric acid (H3PO4), we need to consider the stepwise dissociation of each acid. Let's start with oxalic acid:
1. Oxalic acid (H2C2O4) dissolves in water and the first dissociation step occurs:
H2C2O4 ⇌ H+ + HC2O4-
The equilibrium expression for this step is:
K1 = [H+][HC2O4-]/[H2C2O4]
2. Next, the HC2O4- ion also can react with water and undergo the second dissociation:
HC2O4- ⇌ H+ + C2O42-
The equilibrium expression for this step is:
K2 = [H+][C2O42-]/[HC2O4-]
Now let's move on to phosphoric acid:
1. Phosphoric acid (H3PO4) dissolves in water, and the first dissociation step occurs:
H3PO4 ⇌ H+ + H2PO4-
The equilibrium expression for this step is:
K1 = [H+][H2PO4-]/[H3PO4]
2. Next, the H2PO4- ion can also react with water and undergo the second dissociation:
H2PO4- ⇌ H+ + HPO42-
The equilibrium expression for this step is:
K2 = [H+][HPO42-]/[H2PO4-]
3. Lastly, the HPO42- ion can react with water and undergo the third dissociation:
HPO42- ⇌ H+ + PO43-
The equilibrium expression for this step is:
K3 = [H+][PO43-]/[HPO42-]
These equilibrium reactions and expressions represent the stepwise dissociation of oxalic acid and phosphoric acid. Note that the values of the dissociation constants (K1, K2, K3) can vary depending on the temperature and concentration.