Question

What is the molarity of an H3PO4 solution if 362 mL of the solution are completely titrated by 849 mL of 0.128 M Ba(OH)2 solution? (You will need to write a balanced chemical equation because this titration is NOT 1:1.)

0.450 M

0.200 M

0.300 M

0.0364 M

Answer 1

The balanced chemical equation between
`H_(3)PO_(4) and Ba(OH)_(2)` :

`2H_(3)PO_(4)(aq) + 3Ba(OH)_(2)(aq) -->Ba_(3)(PO_(4))_(2)(aq)+ 6H_(2)O(l)`

Moles of
`Ba(OH)_(2) =849 mL * (1L)/(1000mL) * (0.128 mol)/(L) = 0.108672 mol`

Moles of
`H_(3)PO_(4)` =
`0.108672 mol Ba(OH)_(2) * ( 2 molH_(3)PO_(4))/(3 mol Ba(OH)_(2)) = 0.072448 mol H_(3)PO_(4)`

Molarity of
`image`

Correct answer is 0.200 M