To convert 12 g of NaH2PO4 completely into Na3PO4, the volume of 1molar NaOH required is

Method (I) NaH2PO4+2NaOH→Na3PO4+2H2O 120g                    2x40 12g                         X X= 8gWNaOH required = 8gMNaOH =  1M∴1=840X1000V(ml)   VNaOH = 200mlAlternate methodNaH2PO4→Na3PO4Basicity =2At neutralization pointNo.of gm equivalents of NaH2PO4 = No.of gm equivalents of NaOHWGEW=VbNb1000121202=Vb(1)1000Vb=200mlVol. of NaOH required = 200ml