A titration involves adding a reactant of known quantity to a solution of an ano

Question

A titration involves adding a reactant of known quantity to a solution of an another reactant while monitoring the equilibrium concentrations. This allows one to determine the concentration of the second reactant. The equation for the reaction of a generic weak acid HA with a strong base is HA(aq)+O H (aq) A (aq)+ H 2 O(l)

A certain weak acid, HA , with a K a value of 5.61× 10 6 , is titrated with NaOH .

Part A A solution is made by titrating 8.00 mmol (millimoles) of HA and 3.00 mmol of the strong base. What is the resulting pH?. pH = SubmitHintsMy AnswersGive UpReview

Part Part B More strong base is added until the equivalence point is reached. What is the pH of this solution at the equivalence point if the total volume is 42.0 mL ?

Explanation / Answer

Part A)

Ka = 5.61 x 10^-6

pKa = -log (5.61 x 10^-6) = 5.25

HA   + OH-    ----------------> A- + H2O

8           3                               0          0

5           0                               3

pH = pKa + log [salt / acid]

    = 5.25 + log [3 / 5]

   = 5.03

pH = 5.03

Part B)

At equivalence point salt only remains. so

salt concentration = 8 / 42 = 0.190 M

pH = 7 + 1/2 (pKa + log C)

    = 7 + 1/2 (5.25 + log 0.190)

    = 9.26

pH = 9.26

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