chemistry
posted by What? .
What volume in mL of 0.0985 M sodium hydroxide solution is required to reach the equivalence point in the complete titration of a 15 mL sample of 0.124 M phosphoric acid?

H3PO4 + 3NaOH ==> 3H2O + Na3PO4
mols H3PO4 = M x L = ?
Using the coefficients in the balanced equation, convert mols H3PO4 to mols NaOH. That is mols H3PO4 x 3 = mols NaOH.
Now M NaOH = mols NaOH/L NaOH. YOu know M and mols, solve for L NaOH and convert to mL. 
35.7 mL

15mL x(1L/1000mL)x(0.124mols/mol)x (3molNaOH/1molH3PO4)(1L/0.0985mol)x1000mL/1L= 56.6mL
dont cancel out the L to mL conversion just do this step by step, if its wrong correct me idk how it would be wrong tho i did exactly what the book did