What chemical compounds might be present in drinking water?

# 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) H2PO4 −(aq) = H+(aq) + HPO4 2−(aq) HPO4 2−(aq) = H+(aq) + PO4 3−(aq)
- 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.

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