For a solution that is 0.164 M NH3 and 0.102 M NH4Cl calculate the ph. of the solution

Question

I would like to know how to calculate the ph of this question

Answer 1

We can use a form of the Henderson-Hasselbalch equation for this problem.

pH = pK_a + log base conc. / salt conc.

First we have to know the pKa of the conjugate acid to NH3 which is NH4. To find this we need to look up the pKb for ammonia, which is found to be 4.75. To find the corresponding pHa use pKa + pKb = 14 and solve for pKb. 14 - 4.75 = 9.25.

Now we have enough information to calculate the pH from the first equation.

pH = 9.25 + log 0.164/0.102 = 9.46.