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Q.    0.05 M ammonium hydroxide solution is dissolved in 0.001 M ammonium chloride solution . What will be the  O H -  ion concentration of this solution :  K b N H 4 O H   =   1 . 8 × 10 - 5

1         3 . 0   × 10 - 3                       2         9 . 0   × 10 - 4 3         9 . 0   × 10 - 3                       4         3 . 0   × 10 - 4

Dear Student,

According to Henderson-Haselbach equation, pOH=pKb- log[Base][Salt]pOH=pKb- log[NHOHl][NH4Cl]or, pOH= -log (1.8×10-5)-log(0.05)(0.001)              =-[log(1.8)-5log10]-log (50)              =-0.255+5-1.69              =4.74-1.69              =3.05or, -log [OH-]=3.05or. [OH-] =10-3.05 = 8.9×10-4  9×10-4Hence, correct answer is (2)

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