Final answer:
The van't Hoff factor (i) for potassium phosphate, K₃PO₄, is 5 because it dissociates into five ions (4 K⁺ and 1 PO₄³⁻) in an ideal dilute solution. Measured values of i can be lower due to ionic interactions at higher concentrations that inhibit full dissociation.
Step-by-step explanation:
The van't Hoff factor (i) for a compound such as potassium phosphate, K₃PO₄, is calculated based on the number of ions it dissociates into when dissolved in water. Potassium phosphate breaks down into four potassium ions (K⁺) and one phosphate ion (PO₄³⁻), making a total of five ions. Therefore, the ideal van't Hoff factor is 5, representing the number of particles formed per formula unit in solution.
In practice, the measured van't Hoff factor can be lower than the ideal one due to interactions between the ions at higher concentrations, which can prevent the full dissociation expected from the stoichiometry of the salt. Consequently, at concentrations higher than 0.001 M, we may observe a decrease in the van't Hoff factor due to the reduced effective concentration of dissociated ions.
However, for the purpose of this explanation, we are considering the ideal scenario, which assumes total dissociation at sufficiently low concentrations. Therefore, for potassium phosphate in a dilute solution, the ideal van't Hoff factor will indeed be 5.