A 0.411 g sample of potassium hydrogen phthalate, KHC8H4O4 (MM = 204.44 g/mol) is dissolved in 50 mL of deionized water in a 125-Erlenmeyer flask. The sample is titrated to the phenolphthalein endpoint with 15.17 mL of a sodium hydroxide solution. What is the molar concentration of the NaOH solution?

Answer :

Answer: The molarity of NaOH solution is 0.1325 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 = 0.411 g

Molar mass of KHP = 204.44 g/mol

Putting values in above equation, we get:

[tex]\text{Moles of KHP}=\frac{0.411g}{204.44g/mol}=0.00201mol[/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, 0.0027 moles of KHP will react with = [tex]\frac{1}{1}\times 0.00201=0.00201mol[/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 = 0.00201 moles

Volume of solution = 15.17 mL  = 0.01517 L      (Conversion factor:  1 L = 1000 mL)

Putting values in above equation, we get:

[tex]\text{Molarity of NaOH }=\frac{0.00201mol}{0.01517L}=0.1325M[/tex]

Hence, the molarity of NaOH solution is 0.1325 M.

The molarity of NaOH solution is 0.1325 M.

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

Number of moles  = Given mass  / Molar mass

Given mass of KHP = 0.411 g

Molar mass of KHP = 204.44 g/mol

On substituting the values:

Number of moles  = 0.411 g  / 204.44 g/mol

Number of moles = 0.00201 moles

The chemical reaction for the reaction of KHP and NaOH follows

[tex]KHC_8H_4O_4+NaOH---- > KNaC_8H_4O_4+H_2O[/tex]

By Stoichiometry of the reaction:

1 mole of KHP reacts with 1 mole of NaOH

So, 0.0027 moles of KHP will react with =  of NaOH.

Calculation for Molarity:

Molarity =  Moles of solute / Volume  of solution

Given:

Moles of NaOH = 0.00201 moles

Volume of solution = 15.17 mL  = 0.01517 L    

On substituting the values:

Molarity =  0.00201 moles / 0.01517 L

Molarity = 0.1325 M

Hence, the molarity of NaOH solution is 0.1325 M.

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