How many mL of 0.200 M H3PO4(aq) must be added to 25.0 mL of 0.0888 M BaCl2(aq) to precipitate all the barium as barium phosphate?
Write the equation and balance it.
Convert BaCl2 to mols. mols = M x L = ?
Use the coefficients in the balanced equation to convert mols BaCl2 to mols H3PO4.
Now M H3PO4= mols H3PO4/L H3PO4. You khoow M and mols, solve for L and conert to mL.