Use Use primary standard to determine unknown concentration

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 28.59mL of a barium hydroxide solution are needed to neutralize 2.228 grams of KHP, what is the concentration (mol/L) of the barium hydroxide solution?

Answer 1

Here is how you do this, without having to contact one of us and book a session.

You have a reaction between the KHP (a monoprotic acid) and barium hydroxide, Ba(OH)₂. This is a neutralization reaction which forms a salt (barium potassium phthalate) plus water. We should write the correctly balanced equation before we begin our calculations.

We have the following reaction:

2KHP + Ba(OH)₂ ==> Ba(KP)₂ + 2H₂O

First, we'll figure out how many moles of KHP we have present. The molar mass of KHP is 204.2 g / mole.

Thus, 2.228 g x 1 mol / 204.2 g = 0.01091 moles KHP

Next, using the balanced equation, we'll figure out how many moles of Ba(OH)₂ it took to neutralize this amount of KHP:

0.01091 mol KHP x 1 mol Ba(OH)₂ / 2 mol KHP = 0.005455 moles Ba(OH)₂

Finally, we'll calculate the concentration of the Ba(OH)₂ since we know the moles and the volume:

0.005455 mol / 0.02859 L = 0.1908 mol/L = 0.1908 M Ba(OH)₂