n 1  :  a phosphate NaH₂PO₄ of sodium containing one sodium atom per molecule that with the phosphate containing two sodium atoms per molecule constitutes the principal buffer system of the urine - called also monobasic sodium phosphate , odium acid phosphate , odium dihydrogen phosphate   2  :  a phosphate Na₂HPO₄ of sodium containing two sodium atoms per molecule that is used in medicine as a laxative and antacid - called also dibasic sodium phosphate   3  :  a phosphate Na₃PO₄ of sodium containing three sodium atoms per molecule that is used chiefly in cleaning compositions and in water treatment .
 
 
 
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