Question

I know how to solve the rest of this problem but I dont understand how we get this equation to start with

4. Calculate the pH after 0.013 mol of gaseous HCl is added to 260.0 mL of the following buffered solution (Kb, NHB 1.76 x 10) 0.22 M NH3 and 0.45 M NH4Br

Answer 1

Answer:

Given,

To determine te pH

Consider,

260 ml of 0.22 M NH3 = 0.260 * 0.22

= 0.0572 mole.

260 ml of 0.45 M NH4Br = 0.260 * 0.45

= 0.117 mole.

PKb (NH3) = - log (1.76 * 10^-5)

PKb (NH3) = 4.75.

Now,

Henderson equation is given below

POH = PKb + log [salt] / [base]

Substitute values in above expression

POH = 4.75 + log [(0.117 + 0.013) / (0.0572 - 0.013)]

POH = 5.22

PH = 14 - 5.22

PH = 8.78