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Arrange the following 0.10 M solutions from most acidic to most basic. Justify your rankings.
KOH

KNO3

KCN

NH4Cl

HCl


Sagot :

KOH is an alkali metal hydroxide and so would be a strong base. HCl is a hydrogen halide in solution, which would be a strong acid (the exception would be HF). There are no other strong bases or acids in this list, so these two substances will comprise our bookends.

KNO3 is a salt produced during the neutralization reaction between KOH and HNO3; the former is (as we just noted) a strong base, and the latter is a strong acid. The salt consisting of the conjugate acid and base of a strong base and acid, respectively, produces a neutral solution in water. So, the KNO3 would be neutral.

KCN in solution consists of the ions K+ and CN-; K+, as we just went through, is the conjugate acid of KOH, a strong base. CN- is the conjugate base of HCN, a weak acid in solution. Since the resultant salt, KCN, is the neutralization product of a strong base and a weak acid, it will be slightly basic in solution (the CN- is a stronger base than K+ is as an acid). So, the KCN solution would be slightly basic.

NH4Cl dissociates in solution to give NH4+ and Cl-. NH4+, as the conjugate acid of the weak base ammonia, NH3, will donate an H+ in water. Cl- is the conjugate base of a strong acid, HCl. The neutralization product of a strong acid (HCl) and a weak base (NH3) would be slightly acidic. So, the solution of NH4Cl would be slightly acidic.

Ranking the solutions from most acidic to most basic (note: it’s important that the solutions have the same concentrations), we get:

HCl (strong acid)
NH4Cl (weak acid salt)
KNO3 (neutral salt)
KCN (weak basic salt)
KOH (strong base).