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To standardize a solution of NaOH before using it in a titration of an unknown acid, you dissolve 3.56 grams of potassium hydrogen phthalate (KHP) into 100 mL of H2O. You then titrate the KHP with your sodium hydroxide solution and reach the endpoint after adding 20.9 mL of NaOH. What is the molarity of your sodium hydroxide solution? (Molecular Mass of KHP = 204.22 g/mol)

Answer :

Answer: The molarity of your sodium hydroxide solution is 0.813 M

Explanation:

Molarity is defined as the number of moles of solute dissolved per liter of the solution.

[tex]Molarity=\frac{n\times 1000}{V_s}[/tex]

where,

n= moles of solute  

[tex]V_s[/tex] = volume of solution in ml = 100 ml

moles of solute (KHP)  =[tex]\frac{\text {given mass}}{\text {molar mass}}=\frac{3.56g}{204.22}=0.017mol[/tex]

[tex]Molarity=\frac{0.017\times 1000}{100ml}=0.17[/tex]

According to the neutralization law:

[tex]n_1M_1V_1=n_2M_2V_2[/tex]

where,

[tex]M_1[/tex] = molarity of KHP solution = 0.17 M

[tex]V_1[/tex] = volume of KHP  solution = 100 ml

[tex]M_2[/tex] = molarity of NaOH solution = ?

[tex]V_2[/tex] = volume of NaOH solution = 20.9 ml

[tex]n_1[/tex] = valency of KHP = 1

[tex]n_2[/tex] = valency of NaOH = 1

[tex]1\times 0.17\times 100=1\times M_2\times 20.9[/tex]

[tex]M_2=0.813M[/tex]

Thus the molarity of your sodium hydroxide solution is 0.813 M

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