Reaction of orthophosphoric acid with soda ash (Na2CO3) The reaction of orthophosphoric acid (H3PO4) with soda ash ultimately yields which industrial phosphate product (after appropriate neutralization and dehydration/condensation steps)?

Introduction / Context:
Soda ash (Na2CO3) neutralizes phosphoric acid to sodium phosphates. Subsequent thermal dehydration/condensation steps can convert orthophosphate salts into condensed phosphates such as sodium tripolyphosphate (STPP), widely used in detergents and some food applications.

Given Data / Assumptions:

• Acid–base neutralization between H3PO4 and Na2CO3.
• Controlled stoichiometry to reach desired sodium-to-phosphorus ratio.
• Heating to drive off water and condense orthophosphates to polyphosphates.

Concept / Approach:
Neutralization yields mono-, di-, or trisodium phosphate depending on Na2CO3/H3PO4 ratio. Calcination dehydrates and polymerizes these to condensed phosphates. For STPP (Na5P3O10), appropriate feed blending and thermal treatment are applied. Organic phosphates like tricresyl or tributyl phosphate require esterification of phosphorus oxychloride or phosphoric acid with alcohols/phenols, not simple soda ash neutralization. Nitrophosphate is made via nitric acid digestion of rock phosphate, not via Na2CO3 neutralization.

Step-by-Step Solution:

Verification / Alternative check:
Process descriptions for STPP list feedstocks as H3PO4 plus Na2CO3/NaOH/NaHCO3, followed by spray drying and calcination to form Na5P3O10.

Why Other Options Are Wrong:

• Tricresyl/tributyl phosphate: Organic esters, not formed by soda ash neutralization.
• Nitrophosphate: Produced via nitric acid route from rock phosphate.

Common Pitfalls:
Assuming any phosphate product can result from simple neutralization; condensed phosphates require subsequent thermal steps.

Final Answer:
sodium tripolyphosphate (STPP)