To write net equations for the dissociation of phosphoric acid (H3PO4), we need to consider each step individually:
(a) Net equations for the three steps of dissociation of phosphoric acid (H3PO4):
1. The first dissociation step:
H3PO4 ⇌ H+ + H2PO4-
Net equation: H3PO4 → H+ + H2PO4-
2. The second dissociation step:
H2PO4- ⇌ H+ + HPO4^2-
Net equation: H2PO4- → H+ + HPO4^2-
3. The third dissociation step:
HPO4^2- ⇌ H+ + PO4^3-
Net equation: HPO4^2- → H+ + PO4^3-
(b) To prepare disodium phosphate (Na2HPO4(s)) from a solution of phosphoric acid (0.500 molar) and a solution of sodium hydroxide base (0.500 molar), you can follow these steps:
1. Write the balanced chemical equation for the reaction between phosphoric acid and sodium hydroxide:
H3PO4 + 2 NaOH → Na2HPO4 + 2 H2O
2. Determine the moles of each reactant using their molarity (moles = molarity x volume in liters):
Moles of H3PO4 = 0.500 mol/L x volume in liters
Moles of NaOH = 0.500 mol/L x volume in liters
3. Based on the stoichiometry of the reaction equation, react the moles of phosphoric acid and sodium hydroxide in a 1:2 ratio to form disodium phosphate.
4. After the reaction, the resulting solution will contain disodium phosphate (Na2HPO4) which can be isolated by evaporating the water to obtain the solid compound.
By following these steps, you can prepare disodium phosphate from phosphoric acid and sodium hydroxide solution.
