What is the molar concentration of a phosphoric acid (h3po4) solution if 55.5 ml of the solution requires 35.5 ml of .150 m naoh to completely react with the phosphoric acid?

The  molar  concentration  of H3PO4  solution  is calculated  as below

find the  moles of NaOH  reacted =molarity x volume
= 35.5 x0.150 = 5.325  moles

write a balanced  reacting  equation
=NaOH +3 H3PO4 = Na3PO4 + 3H2O

by  use of reacting ratio between NaOH  to H3PO4  which  is 1:3  the moles of  H3Po4 is therefore
= 5.325moles/3= 1.775 moles

molar  concentration is therefore of H3PO4=  moles /volume
=1.775/55.3 = 0.0320 M of H3PO4

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