Question

Calculate the ph for the following solutions:

0.10 M NH₃

50 mL 0.10 M NH₃ + 50 mL 0.10 M NH₄NO₃

Answer 1

pKb of NH3 is 9.25 from the text book its a standard value

Part A

0.10 M NH₃

there is direct formula finding the pOH of the week base

pOH = 1/2(pKb -logC)

where C is the concentration of NH3 = 0.1

pOH = 1/2 (9.25 - log0.1))

pOH = 1/2 (9.25 - (-1))

pOH = 1/2 (10.25)

pOH = 5.12

now use the formula

pH + pOH = 14

pH = 14-pOH = 14 - 5.12 =

pH = 8.88

PartB

use the hander son equation

pOH = pKb + log([salt] / [Acid])

pOH = 9.25 + log (0.1/ 0.1)

pOH = 9.25

now use the formula

pH + pOH = 14

pH = 14-9.25

pH = 4.75