Summary of Section 3

• Phosphate is used in fertilisers and excess phosphate in natural water can cause eutrophication.
• Phosphorus has several acids including phosphoric and phosphorus acid. Note the higher oxidation number, or oxidation state, is indicated by the suffix -ic and the lower oxidation state by the suffix -ous.
• Generally for oxoacids if more than two oxidation numbers are involved, the prefixes per- and hypo- are used as well where per- denotes the highest oxidation number and hypo- the lowest oxidation number.
• Some acids of phosphorus are polyprotic. For instance, phosphoric acid:
   
  H₃PO₄(aq) = H⁺(aq) + H₂PO₄⁻(aq)

  (Equation 21)
  H₂PO₄⁻(aq) = H⁺(aq) + HPO₄²⁻(aq)

  (Equation 22)
  HPO₄²⁻(aq) = H⁺(aq) + PO₄³⁻(aq)

  (Equation 23)
• Deprotonation of an acid yields its conjugate base or anion. In Equation 21 H₂PO₄⁻ is the conjugate base of phosphoric acid.
• Oxoacids and oxoanions can polymerise by condensation.
• Phosphorus also forms polyacids containing two or more acidic phosphorus centres.
• Polyphosphate can form chain or ring polymers.
• Adenosine triphosphate (ATP) stores energy in the body which is released upon its hydrolysis to adenosine diphosphate (ADP).
• The negative charges on ATP, ADP and DNA are counterbalanced by cations, usually magnesium.