Stoichiometry, concentration of solutions: Ba(OH)2 and H3PO4

[9781133886563]

Homework Statement

What volume of 0.0521 M Ba(OH)₂ is required to react completely with 24.50 mL of 0.141 M H₃PO₄? Phosphoric acid is a triprotic acid.

Answer: volume of 0.0521 M Ba(OH)₂ required = 99.5 mL

2. The attempt at a solution
1. I begin by balancing the equation: 3Ba(OH)₂ + 2H₃PO₄ → Ba₃(PO₄)₂ + 6H₂O

2. I use M = Molarity = mol solute / L solution to find the mols of H₃PO₄... mol = 0.141 × 24.50 mL = 3.45 mol

3. According to the mole ratio... 3 × 3.45 mol of Ba(OH)₂ = 10.36 mol of Ba(OH)₂ needed.

4. M = mol/L ... mL = 10.36 mol / .0521 M = 199.0 mL of Ba(OH)₂ needed, which is a wrong answer.

These are the steps I am taking. I must be making a mistake since I know that the answer is 99.5 mL.

 

[Saitama]

3. According to the mole ratio... 3 × 3.45 mol of Ba(OH)₂ = 10.36 mol of Ba(OH)₂ needed.

Check this again.

 

[Borek]

Note that your answer is exactly twice too large (which points in exactly the same direction Pranav-Arora alredy signaled).

 

[9781133886563]

I see it now. The mole ratio is 3/2.

Thank you both.