Number of moles of NH4Cl= concentration of NH4Cl× volume of NH4Cl =0.0504M×5mL=0.2520 millimoles Total volume of solution in mixture = Volume of NH4Cl solution + volume of NH3solution =5+2=7mL Concentration of NH4Cl in mixture =
NumberofmolesofNH4Cl
Totalvolume
=
0.2520millimole
7mL
=0.036M NumberofmolesofNH3=concentrationofNH3×volumeofNH3 =0.0210×2=0.042 millimole Concentration of NH3 in mixture =
NumberofmolesofNH3
Totalvolume
=
0.042
7
=0.006M According to Handerson’s equation pOH=pKb+log
[Salt]
[Base]
[Salt]=[NH4Cl] [Base]=[NH3] pOH=−logKb+log
0.036
0.006
pOH=−log(1.8×10−5)+0.7782 pOH=5.523 ∵ pOH=−log[OH−] So, [OH−]=2.9×10−6≈3×10−6 ∴ x=3