Question

You are going to standardize your sodium hydroxide by titrating with potassium hydrogen phthalate. As an example, you dissolve 0.3365 g of potassium hydrogen phthalate, otherwise known as KHP (KHC8H4O4) in water in a 250.0 mL Erlenmeyer flask and then add phenolphthalein indicator. You then titrate with your sodium hydroxide solution, which is in a buret, and you determine that the equivalence point is at 12.44 mL of your sodium hydroxide solution. Determine the molarity of your sodium hydroxide solution. What color will the solution of potassium hydrogen phthalate turn to determine when the equivalence point has been reached?

Answer 1

NaOH + KHP =NaKP + H2O

Number of moles of KHP= amount of KHP (g)/mw of KHP(g/mol)

                                                 = 0.3365 g/204.2g/mol= 0.00164789 moles

According to the above balanced equation

At the endpoint

Number of moles of KHP= Number of moles of NaOH

0.00164789 = Molarity of NaOH X Volume of NaOH solution in L

0.00164789 = Molarity of NaOH X 12.44/1000

Molarity of NaOH= 0.13 M

Phenolphthalein indicator is colorless in acidic medium and it shows pink color in basic medium.

Solution will turn of faint pink color just after equivalence point.