Anna Calculating the pH of a weak acid titrated with a strong bese An analytical

Question

Anna Calculating the pH of a weak acid titrated with a strong bese An analytical chemist is titrating 179,2 mL. of a 0.4000 f solution of nitrous acid (HNO,) with a 1.200 M solution of NaOH. The pX, of nitrous acid is 3.35 Calculate the pH of the acid solution after the chemist has added 21.54 mL of the NaOH solution to it. Note for advanced students: you may assume the final volume equals the initial volume of the solution plus the volume of NaOH solution added Round your answer to 2 decimal places. PH

Explanation / Answer

no of moles of HNO2 = molarity * volume in L

                                = 0.4*0.1792    = 0.07168moles

no of moles of NaOH   = molarity * volume in L

                                   = 1.2*0.02154    = 0.025848moles

             HNO2    +   NaOH ----------------> NaNO2 + H2O

I            0.07168       0.025848 0

C          -0.025848    -0.025848                 0.025848

E          0.045832         0                          0.025848

   Pka of HNO2 = 3.15

   PH   = Pka + log[NaNO2]/[HNO2]

          = 3.15 + log0.025848/0.045832

         = 3.15 -0.2487

         = 2.90

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