Determine the concentration of hydroxyl ions in 0.4M NH_{4OH solution having} 1)no NH₄Cl 2)5.35gm of NH₄Cl

ionization constant of NH₄OH is 1.8*10^-5

Hi Tejas,

1) NH4Cl---->NH4⁺ + Cl^-

    0.4(1-x)      0.4x    0.4x

    0.4*x²/(1-x)=1.8*10^-5

     x²/(1-x)=4.5*10^-4

     as the value of ionization constant is less 1-x≈1

      x²=4.5*10^-4

      [OH^-]=2.12*10^-2

2)NH₄Cl completely undergoes dissociation

   5.35 g of NH₄Cl is 0.1 moles

    x(0.1+x)/(0.4-x)=1.8*10^-5

    x²+x(0.1+1.8*10^-5)-7.2*10^-4=0

    0.1+1.8*10^-5≈01

    x²+0.1x-7.2*10^-4=0

    x=6.745*10^-3

   [OH^-]=6.745*10^-3