A 10.0-mL sample of an unknown H3PO4 solution requires 112 mL of 0.100 M KOH to completely react with the H3PO4. What was the concentration of the unknown H3PO4 solution

The correct answer is 0.373 M.

Explanation:

The reaction will be,

H3PO4 (aq) + 3KOH (aq) ⇔ 3H2O (l) + K3PO4 (aq)

Based on the given information, the molarity of the solution KOH is 0.100 M, the volume of the solution given is 112 ml or 0.112 L.

The molarity of the solution with respect to KOH is,

M = Moles/Volume of Solution (liters)

Moles of solute = Molarity * Volume of solution

Moles = 0.100 M * 0.112 L

= 0.0112 moles

From the reaction it is clear that 3 moles of KOH needed 1 mole of H3PO4, thus, 0.0112 moles of KOH will require,

1/3 * 0.0112 = 0.00373 moles of H3PO4

The volume of the H3PO4 solution is 10 ml or 0.01 L.

The molarity of the solution will be,

M = Moles/ Volume of Solution (liters)

M = 0.00373/0.01 = 0.373 M

Thus, the concentration of the solution is 0.373 M.