Identify the correct chemical formula for sodium tripolyphosphate (STPP), a common builder in detergents and a phosphate fertiliser intermediate.

Introduction / Context:Sodium tripolyphosphate (STPP) is widely used as a sequestrant in detergents and appears in phosphate fertiliser process streams. Correct stoichiometry helps with mass balances and environmental compliance calculations (e.g., phosphorus loading).

Given Data / Assumptions:

• Compound name: sodium tripolyphosphate.
• We seek the empirical formula reflecting three phosphate units and five sodium cations.

Concept / Approach:“Tripolyphosphate” indicates three tetrahedral phosphate units linked via two P–O–P bridges, carrying an overall charge of 5− balanced by five Na+. Hence the formula Na5P3O10 is standard in handbooks and labels for STPP (often as the hexahydrate in commerce, but the anhydrous formula is Na5P3O10).

Step-by-Step Solution:

Verification / Alternative check:Material safety data sheets and chemical catalogs list STPP as Na5P3O10 (with hydrates noted separately), verifying the formula.

Why Other Options Are Wrong:

• Na4P3O8 and Na3P4O6: incorrect stoichiometry and phosphorus count.
• Na2PO4 or Na3PO4: monophosphates, not tripolyphosphate.

Common Pitfalls:Confusing the anhydrous formula with hydrate compositions; hydrates add water molecules but do not alter the Na:P:O ratio of the anion.

Final Answer:Na5P3O10