Zinc pyrophosphate explained

Zinc pyrophosphate (Zn₂P₂O₇) is an ionic inorganic chemical compound composed of Zn²⁺ cations and pyrophosphate anions.

Preparation

Zinc pyrophosphate can be obtained from the thermal decomposition of zinc ammonium phosphate.^[1]

2 ZnNH₄PO₄ → Zn₂P₂O₇ + 2 NH₃ + H₂O

It can also be obtained from the reaction between sodium carbonate, zinc oxide, and ammonium dihydrogen phosphate.^[2]

Na₂CO₃ + 2 ZnO + 2 (NH₄)H₂PO₄ → Zn₂P₂O₇ + 2 NaOH + 2 NH₃ + 2 H₂O + CO₂

It is also produced when a strongly acidic solution of zinc sulfate is heated with sodium pyrophosphate.^[3]

2 ZnSO₄ + Na₄P₂O₇ → Zn₂P₂O₇ + 2 Na₂SO₄

Another method is precipitating zinc as a phosphate, then heating over 1123 K.

Properties

Zinc pyrophosphate is a white crystalline solid that is insoluble in water.^[4] On heating in water, it decomposes to form Zn₃(PO₄)₂ and ZnHPO₄. It crystallizes in the monoclinic system. The α-form crystallizes at low temperatures and the β-form crystallizes at high temperatures.^{[1] [2]}

Uses

Zinc pyrophosphate is used as a pigment.^[4] It is useful in gravimetric analysis of zinc.^[5]

Notes and References

1. Calvo. Crispin. 1965-05-01. THE CRYSTAL STRUCTURE AND PHASE TRANSITIONS OF β-Zn 2 P 2 O 7. Canadian Journal of Chemistry. en. 43. 5. 1147–1153. 10.1139/v65-152. 0008-4042. free.
2. Jarboui. A.. Ben Rhaeim. A.. Hlel. F.. Guidara. K. Gargouri. M.. 2010. NMR study and electrical properties investigation of Zn2P2O7. Ionics. en. 16. 1. 67–73. 10.1007/s11581-009-0333-5. 94790682 . 0947-7047.
3. Book: Ochs, Rudolf. Praktikum der Qualitativen Analyse Für Chemiker · Pharmazeuten und Mediziner. Springer-Verlag. 2013. 978-3-662-28315-8. Berlin, Heidelberg. 117. 860357745.
4. Book: Perry, Dale L.. Handbook of Inorganic Compounds. CRC Press. 2016. 978-1-4398-1462-8. 2nd. Boca Raton, FL. 469. 759865801.
5. Book: Holleman. Arnold F.. Lehrbuch der anorganischen Chemie. Wiberg. Egon. Wiberg. Nils. de Gruyter. 1995. 978-3-11-012641-9. 102nd. Berlin. 1493. 237142268.