PHOSPHORIC ACID - (7664-38-2) - Physical Properties • Chemical Properties • Solubility • Uses/Function • Reactions • Thermochemistry

Introduction

Name: phosphoric acid
* IUPAC
CAS Number: 7664-38-2
Chemical Formula: H₃PO₄
Molar Mass: 97.995181 g
Mass Percent: H 3.0856 %; P 31.607 %; O 65.306 %

Classification

• inorganic

Uses/Function

• "needed in the manufacture of a multitude of products, including fertilizers and detergents, baking powder, and various food products" 1

• "9th most produced chemical in the United States in 1995 - 11.5 megatonnes." 2

• "9th most produced chemical in the United States - 20.95 billion pounds" 3

• "Phosphoric acid is used to make phosphate fertilizers and detergent preparations. The acid is also added to carbonated beverages to increase tartness." 4

Bonding

Thermochemistry

ΔHf° (s): -302.8 kcal/mol 5 = -1,266.92 kJ/mol
ΔHf° (ℓ): -299.8 kcal/mol 5 = -1,254.36 kJ/mol

S° (s): 26.42 cal/(mol•K) 6 = 110.54 J/(mol•K)
S° (ℓ): 36.0 cal/(mol•K) 6 = 150.62 J/(mol•K)

ΔGf° (s): -265.9 kcal/mol 7 = -1,112.53 kJ/mol
ΔGf° (ℓ): -265.7 kcal/mol 7 = -1,111.69 kJ/mol

Reactions

3 Ca(OH)2 (aq) + 2 H3PO4 (aq) → 6 H2O (ℓ) + Ca3(PO4)2 (s)
Ca3(PO4)2 (s beta) + 3 H2SO4 (aq) → 2 H3PO4 (aq) + 3 CaSO4 (s) 8
Ca3(PO4)2 (s beta) + 3 H2SO4 (ℓ) → 2 H3PO4 (ℓ) + 3 CaSO4 (s) 9
3 NaOH (aq) + 1 H3PO4 (aq) → Na3PO4 (aq) + 3 H2O (ℓ) 10
P4O10 (s) + 6 H2O (ℓ) → 4 H3PO4 (aq)
PCl5 (ℓ) + 4 H2O (ℓ) → H3PO4 (aq) + 5 HCl (g)
2 H3PO4 (aq) + 3 CaCO3 (s) → Ca3(PO4)2 (s) + 3 H2O (ℓ) + 3 CO2 (g)
2 H3PO4 (aq) + 3 MgCO3 (s) → Mg3(PO4)2 (s) + 3 H2O (ℓ) + 3 CO2 (g) 11
2 H3PO4 (aq) + 3 Na2SO3 (s) → 2 Na3PO4 (aq) + 3 H2O (ℓ) + 3 SO2 (g) 12

For More Information

Wikipedia

Sources

(1) - Kotz, Treichel, and Weaver. Chemistry & Chemical Reactivity, 6th ed.; Thomson Brooks/Cole: Belmont, CA, 2006; p 1030.
(2) - Chem. Eng. News, 1995, 73 (26), p 39
(3) - Reisch, Mark S.; Top 50 Chemicals Production Turned Back Up in 1987. Chemical & Engineering News, April 11, 1988, pp 30-33.
(4) - Ebbing, Darrell D. General Chemistry 3rd ed.; Houghton Mifflin Company: Boston, MA, 1990; p 345.
(5) - Dean, John A. Lange's Handbook of Chemistry, 12th ed.; McGraw-Hill Book Company: New York, NY, 1979; p 9:4-9:94.
(6) - Dean, John A. Lange's Handbook of Chemistry, 12th ed.; McGraw-Hill Book Company: New York, NY, 1979; p 9:4-9:94.
(7) - Dean, John A. Lange's Handbook of Chemistry, 12th ed.; McGraw-Hill Book Company: New York, NY, 1979; p 9:4-9:94.
(8) - T < 22.9165675122579
(9) - T < 2902.02466837328
(10) - T > -692.288618894123
(11) - T > 18.2291666666672
(12) - T > 94.7931034482751