Question

You want to determine the concentration of acid in a particular solution. To this end, you decide to titrate the acid with a standardized sodium hydroxide solution. You quickly throw together an approximately 0.1 M NaOH solution, and then you realize you need to know the exact concentration of this solution before you can use it for anything meaningful.

1. Using an acid-base titration, 30.65 mL of your NaOH solution were needed to neutralize 0.6923 g of KHP (potassium hydrogen phthalate, KHC8H4O4). What is the actual molarity of the NaOH solution? (HINT: moles acid = moles base)

2. Now that you have standardized your NaOH solution, determine the mass of acetic acid (CH3COOH) dissolved in a 49.77 mL of water if it takes 62.30 mL of your NaOH solution to neutralize it.

Answer 1

1)

moles of KHP = mass / molar mass

                        = 0.6923 / 204.22

                        = 3.39 x 10^-3

moles of KHP = moles of NaOH

moles of NaOH = 3.39 x 10^-3

volume = 30.65 mL = 0.03065 L

molarity of NaOH = moles / volume

                            = 3.39 x 10^-3 / 0.03065

                          = 0.1106 M

molarity of NaOH = 0.1106 M

2)

moles of NaOH = moles of acetic acid

0.1106 x 62.30 / 1000 = 6.89 x 10^-3

moles of acetic acid = 6.89 x 10^-3

mass of acetic acid = moles x molar mass

                                = 6.89 x 10^-3 x 60.0

                                 = 0.413 g

mass of acetic acid = 0.413 g