Potassium hydrogen phthalate, KHC 8 H 4 O 4 , is used to standardize solutions o

Question

Potassium hydrogen phthalate, KHC8H4O4, is used to standardize solutions of bases. The acidic anion reacts with strong bases according to the following net ionic equation:

a) If a 0.780-g sample of potassium hydrogen phthalate is dissolved in water and titrated to the equivalence point with 29.49 mL of NaOH(aq), what is the molar concentration of the NaOH?
_______ M

b) If 50.00 mL of the NaOH(aq) solution is added to an empty beaker and titrated to the equivalence point with 43.79 mL of HClO4(aq), what is the molar concentration of the HClO4?
_______ M

Explanation / Answer

a) Molar mass of HC8H4O4- => 165 g/mol

So moles of  HC8H4O4- => 0.780 g / 165 g/mol => 0.004727 mol

1 eq of  HC8H4O4- reacts with 1 eq of OH- , hence moles of OH- also 0.004727 moles

29.49 mL = 0.02949 L

Molarity of OH- = 0.004727 mol / 0.02949 L => 0.160 M

b) NaOH + HClO4 ----> NaClO4 + H2O

M of HClO4 = 50.00 mL of NaOH x 0.160 M / 43.79 mL => 0.183 M

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