$100 mL$ of a solution contains $0.100 M$ $H X_{3} PO X_{4}$ and $0.0500 M$ $NaH X_{2} PO X_{4}$ . What volume of $0.500 M$ $NaOH$ converts all the phosphorus species completely to $Na X_{3} PO X_{4}$ ? Answer in $mL$ (nearest integer).

Numerical answer type, answer in mL, tolerance 0.5.

Answer: 80 mL

Moles:

H X_{3} PO X_{4} = 0.0100

(

n = 3

for

H X_{3} PO X_{4} PO X_{4} X^{3 -}

) and

NaH X_{2} PO X_{4} = 0.00500

(

n = 2

). Equivalents

= 0.0100 \times 3 + 0.00500 \times 2 = 0.040

NaOH

(0.500 N) volume

= 0.040/0.500 = 0.080 L = 80 mL