Question

Potassium hydrogen phthalate is a solid, monoprotic acid frequently used in the laboratory as a primary standard. It has the unwieldy formula of KHC8H4O4. This is often written in shorthand notation as KHP.

If 35.6 mL of a barium hydroxide solution are needed to neutralize 2.89 grams of KHP, what is the molarity of the barium hydroxide solution?

_______ M

Answer 1

The balanced equation for this reaction is:

The number of moles of KHP is:

$$n(KHP)=\frac {m(KHP)} {M(KHP)} = \frac {2.89 g} {204 g/mol}=0.01416 mol$$

According to the balanced equation, we need twice less moles of barium hydroxide per each mole of KHP. Then, number of moles of the barium hydroxide is equal to 0.5*0.01416 mol = 0.00708 mol.

Now we can calculate the molarity of a barium hydroxide solution:

$$C_M(Ba(OH)_2)=\frac {n(Ba(OH)_2)} {V(Ba(OH)_2)} = \frac {0.00708 mol} {0.0356 L}=0.19897M$$

Answer: the molarity of the barium hydroxide solution is 0.19897M.