A 15.0 mL solution of Ba(OH)₂ is neutralized with 22.4 mL of 0.200 M HCl. What is the concentration of the original Ba(OH)₂ solution?

Answer 1

The question asks for concentration, so we need to get the molarity of the Ba(OH)₂. Remember that in a neutralization question the moles of acid and moles of base will be equal. We can calculate the moles of acid using the molarity and volume of the HCl. The volume must be converted to liters as well.

0.200M * (22.4/1000) = .00448 moles of acid.

The moles of acid or H₃O⁺ must be equal to the moles of OH^- so there are also .00448 moles of OH^-.

Since this problem involves Ba(OH)₂ there are two moles of OH^- per mole of Ba(OH)₂ so we can use a mole conversion like this: 1 mole Ba(OH)₂ / 2 mole OH^-. Using the conversion leaves us with .00224 moles of Ba(OH)₂. The last step is to put the moles of Ba(OH)₂ over the liters to make the molarity.

.00224 moles of Ba(OH)₂/.015 Liters yields a molarity of 0.149M.