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)

Respuesta :

Answer: The molarity of NaOH solution is 0.1196 M

Explanation:

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

[tex]\text{Number of moles}=\frac{\text{Given mass}}{\text{Molar mass}}[/tex]

Given mass of KHP = 0.397 g

Molar mass of KHP = 204.22 g/mol

Putting values in above equation, we get:  

[tex]\text{Moles of KHP}=\frac{0.397g}{204.22g/mol}=0.00194mol[/tex]

The chemical reaction for the reaction of KHP and NaOH follows  

[tex]KHC_8H_4O_4(aq.)+NaOH\rightarrow KNaC_8H_4O_4(aq.)+H_2O(l)[/tex]

By Stoichiometry of the reaction:  

1 mole of KHP reacts with 1 mole of NaOH.  

So, 0.00194 moles of KHP will react with = [tex]\frac{1}{1}\times 0.00194=0.00194mol[/tex] of NaOH.

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

[tex]\text{Molarity of the solution}=\frac{\text{Moles of solute}}{\text{Volume of solution (in L)}}[/tex]

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:  

[tex]\text{Molarity of NaOH }=\frac{0.00194mol}{0.01622L}=0.1196M[/tex]

Hence, the molarity of NaOH solution is 0.1196 M