One mole of ammonia was completely absorbed in one litre solution each of (a) ( 1 M HCl ), (b) ( 1 M CH ₃ COOH ) and (c) ( 1 M H ₂ SO ₄ ) at ( 298 ~K ). The decreasing order for the ( pH ) of the resulting solutions is (Given ( K _ b ( NH ₃ )=4.74 ) )

Step-by-step solution

The reactions involved are as follows: (I) HCl + NH ₃( aq ) NH ₄ Cl (II) CH ₃ COOH + NH ₃( aq ) CH ₃ COONH ₄ (III) H ₂ SO ₄+2 NH ₃( aq ) ( NH ₄ )₂ SO ₄ Now, according to Henderson Haselbach equation p H =p ~K _ a + ( [ A ⁻ ] [ HA ] )=14- pK _ b + ( [ A ⁻ ] [ HA ] )=9.26+ ( [ A ⁻ ] [ HA ] ) Thus, pH depends on the strength of conjugate acid. The order acid strength of the reactants is as follows: CH ₃ COOH NH ₄ Cl ( I )>( III ) .