When 50 mL of 0.1 M NH3 is mixed with 10 mL of 0.1 M HCI then what is the pH of resultant solution? (pKb = 4.75 )
Answers
The correct answer is - 9.26
From the given data, it is obvious that the number of moles of the weak base i.e. the ammonia solution is more than the number of moles of the hydrochloric acid. Also, the pKb value of the weak base has been given as 4.74.
Based on the Henderson-Hasselbach equation, the pH of a buffer solution can be calculated using the formula, pH = 14 - pKb - log [ (B⁺) / (BOH)]
[B+ ] is the molar concentration of the salt or the anion formed and the molar concentration of the weak base is represented as [BOH]. Since it is a buffer solution and the concentration of the salt (NH₄Cl) and the weak base (NH₃) is equal, the fraction will be 1.
So, pH = 14 - 4.74 - log 1.
Calculating from the log tables, we get the answer of pH as 9.26.