Manufacture of sodium tripolyphosphate (STPP) STPP is commercially manufactured by neutralizing phosphoric acid with which sodium base (before dehydration/condensation to the polyphosphate)?

Introduction / Context:
Sodium tripolyphosphate (Na5P3O10) is a major detergent builder. The first step in its production is forming sodium orthophosphates by neutralizing phosphoric acid with an alkali source before calcination to the tripoly form.

Given Data / Assumptions:

• Feed acid: H3PO4.
• Candidate sodium bases: carbonate, bicarbonate, phosphate, silicate.
• Subsequent thermal dehydration/condensation produces STPP.

Concept / Approach:
Industrial routes use Na2CO3 (soda ash), NaHCO3, and/or NaOH to neutralize H3PO4 to mixed sodium phosphates, then spray-dry and calcine to Na5P3O10. Among the listed bases, sodium carbonate is the standard raw material. Sodium phosphate would be a product, not a base reagent; silicate is not used for neutralizing to STPP; bicarbonate is possible but less typical alone compared to Na2CO3.

Step-by-Step Solution:

Verification / Alternative check:
Process descriptions and PFDs cite soda ash (and sometimes NaOH) as the neutralizing agent for STPP manufacture.

Why Other Options Are Wrong:

• Phosphate: It is the product class, not the base used for neutralization.
• Bicarbonate: Usable but not the principal industrial choice in the context given.
• Silicate: Not relevant to STPP synthesis.

Common Pitfalls:
Confusing feed reagents with intermediate or final products in phosphate chemistry.

Final Answer:
carbonate