ACIDS AND BASES Calculating the pH of a weak acid titrated with a strong b... An

Question

ACIDS AND BASES Calculating the pH of a weak acid titrated with a strong b... An analytical chemist is titrating 155.0 ml, of a 0.8300 M solution of nitrous acid (HNO2) with a 0.5600 M solution of NaOHL. The p K, of nitrous acid is 3.35. Calculate the pH of the acid solution after the chemist has added 133.7 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 Check

Explanation / Answer

No of mol of HNO2 taken = M*V

                        = 0.83*155

                        = 128.65 mmol
No of mol of NaOH = M*V

                  = 133.7*0.56

                  = 74.872 mmol

pKa of HNO2 = 3.35

pH of acidic buffer,

pH = pka + log(base/acid)

pH = 3.35 + log(74.872/(128.65-74.872))

     = 3.49

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