Question

Denis titrates 25 mL of a 0.060 M solution of ammonia (NH3) with a 0.020 M solution of hydrochloric acid. A) Write the chemical equation that occurs B) Do you expect the pH of the solution to be acidic, basic or neutral at the equivalence point? Explain. C) Calculate the pH after 20 mL of HCl solution have been added. Hint: Kb(NH3)=1.8*10-5

Answer 1

A)

chemical equation :

NH3 + HCl -------------------> NH4Cl

B)

pH of solution will be acidic

because at equivalence point the salt NH4Cl is formed . it is the salt of weak base and strong acid . so the pH is less than 7

C )

millimoles of NH3 = 25 x 0.06 = 1.5

millimoles of HCl = 0.02 x 20 = 0.4

NH3    +   HCl ----------------> NH4Cl

1.5            0.4                         0

1.1           0.0                          0.4

pKb =-log Kb = -log (1.8 x 10^-5) = 4.74

pOH = pKb + log [NH4Cl / NH3]

pOH = 4.74 + log (0.4 / 1.1)

pOH = 4.30

pH + pOH = 14

pH = 9.70