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Material Safety Data Sheet(MSDS)

Questions And Answer

• Preparation

  Pyrophosphoric acid may be prepared by heating orthophosphoric acid at 215°C:
  2H3PO4 → H4P2O7 + H2O
  The acid solution in pure form can be obtained by ion exchange, passing an aqueous solution of sodium pyrophosphate, Na4P2O7, through a suitable cation exchange column. ;

• Reactions

  The acid has four replacable H+ ions. Its dissociation constants indicate that two H+ ions are strongly acidic while the other two protons are weakly acidic. The first dissociation constant especially is very large:
  H4P2O7 + H2O ↔ H3O+ + H3P2O7¯          Ka1 ~ 10–1
  H3P2O7¯+ H2O ↔ H3O+ + H2P2O72–         Ka2 ~ 1.5x10–2
  PHOSPHORIC ACID, PYRO 701H2P2O72¯ + H2O ↔ H3O+ + HP2O73–      Ka3 ~ 2.7x10–7
  HP2O73¯ + H2O ↔ H3O+ + P2O74¯          Ka4 ~ 2.4x10–10
  Pyrophosphoric acid forms acid salts, such as NaH3P2O7 and Na2H2P2O7. ;

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