# 358ml of an H3PO4 solution is completely titrated by 876mL of 0.0102M Ba(OH)2 solution?

## a) Write the balanced neutralization reaction b) Calculate the molarity of H3PO4 c) Will the pH at the quivalence point be 7, above 7 or below 7

Jun 12, 2016

${H}_{3} P {O}_{4} \left(a q\right) + B a {\left(O H\right)}_{2} \left(a q\right) \rightarrow B a H P {O}_{4} \left(a q\right) + 2 {H}_{2} O \left(l\right)$

#### Explanation:

You will have to check with your teacher and text on this. But it is a fact that phosphoric acid behaves as a $\text{DIPROTIC}$ acid in water.

Given this we can answer the questions according to the reaction:

${H}_{3} P {O}_{4} \left(a q\right) + B a {\left(O H\right)}_{2} \left(a q\right) \rightarrow B a H P {O}_{4} \left(a q\right) + 2 {H}_{2} O \left(l\right)$

Moles of $B a {\left(O H\right)}_{2}$ $=$ $876 \times {10}^{-} 3 \cdot L \times 0.0102 \cdot m o l \cdot {L}^{-} 1$ $=$ $8.94 \times {10}^{-} 3 m o l$.

Given the 1:1 equation, the concentration of the starting acid solution was:

$\frac{8.94 \times {10}^{-} 3 \cdot m o l}{0.358 \cdot L}$ $\cong$ $0.0250 \cdot m o l \cdot {L}^{-} 1$ with respect to ${H}_{3} P {O}_{4}$.

At the equivalence point, given the basicity of biphosphate, $p H > 7$.

Note that I assume you are an undergrad not an A-level student, and at this level you should know that phosphoric acid is a diacid and that aqueous titration with base contains just 2 equivalence points.. See here for further details.