A 0.397-g sample of potassium hydrogen phthalate, KHC8H4O4 (molar mass = 204.22 g/mol) is dissolved with 50 mL of deionized water in a 125-mL Erlenmeyer flask. The sample is titrated to the phenolphthalein endpoint with 16.22 mL of a sodium hydroxide solution. What is the molar concentration of the NaOH solution? (Show all calculations)

The molarity of NaOH solution is 0.1196 M

Explanation:

To calculate the number of moles, we use the equation:

Given mass of KHP = 0.397 g

Molar mass of KHP = 204.22 g/mol

Putting values in above equation, we get:  

The chemical reaction for the reaction of KHP and NaOH follows  

By Stoichiometry of the reaction:  

1 mole of KHP reacts with 1 mole of NaOH.  

So, 0.00194 moles of KHP will react with = of NaOH.

To calculate the molarity of NaOH, we use the equation:

We are given:

Moles of NaOH = 0.00194 moles

Volume of solution = 16.22 mL  = 0.01622 L      (Conversion factor:  1 L = 1000 mL)

Putting values in above equation, we get:  

Hence, the molarity of NaOH solution is 0.1196 M

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