Final answer:
The ideal van't Hoff factor for Na3PO4 is 4, corresponding to three Na+ ions and one PO43- ion when dissolved.
Step-by-step explanation:
The ideal van't Hoff factor for Na3PO4 is determined by the number of ions it forms when it dissolves in water. When Na3PO4 dissolves, it separates into four ions: three sodium ions (Na+) and one phosphate ion (PO43-). Therefore, the ideal van't Hoff factor (i) for Na3PO4 is 4. This factor is important when calculating colligative properties of solutions, such as boiling point elevation (ΔTb) and freezing point depression (ΔTf), which depend on the number of solute particles in a solution.
We must remember that the ideal van't Hoff factor assumes total dissociation of the ionic compound, which is only strictly accurate for dilute solutions (less than 0.001 M). In more concentrated solutions, ionic interactions can reduce the actual number of free ions and therefore the actual van't Hoff factor may be less than ideal. Nevertheless, for dilute solutions, the ideal van't Hoff factor can be used directly in colligative property equations.