Question

In: Chemistry

A 25.0 mL sample of a 0.150 M weak acid, Ka = 4.6 x 10−5 ,...

A 25.0 mL sample of a 0.150 M weak acid, Ka = 4.6 x 10−5 , is titrated with 0.200 M NaOH. Calculate the pH when 10.0 mL of the base has been titrated into the acid.

Solutions

Expert Solution

no of moles of acid HA   = molarity * volume in L

                                       = 0.15*0.025    = 0.00375 moles

no of moles of NaOH   = molarity * volume in L

                                     = 0.2*0.01   = 0.002mole

                    HA + NaOH ----------------> NaA + 2H2O

        I         0.00375      0.002                          0

        C       -0.002         -0.002                        0.002

       E       0.00175          0                              0.002

                     Ka   = 4.6*10^-5

              PKa   = -logKa

                        = -log4.6*10^-5

                       = 4.3372

         PH    = Pka + log[NaA]/[HA]

                 = 4.3372 + log0.002/0.00175

                = 4.3372 + 0.05799

                = 4.3951 >>>>>answer


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