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The acidic strength decreases in the order : HCl gt H_(2)S gt PH_(3). Explain. Or The acidic strength of compounds increases in the order : PH_(3) lt H_(2)S lt HCl. |
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Answer» Solution :The strength of an acid depends upon the stability of the anion (i.e., conjugate base) it gives after release of a proton. Now the disssociation of `PH_(3), H_(2)S` and HCl in aqueous solution occurs as FOLLOWS : `{:(PH_(3)(g)+aq rarr H^(+) (aq) + H_(2)P^(-) (aq), K_(a) = 1.6 xx 10^(-29)),(H_(2)S(g) + aq rarr H^(+) (aq) + HS^(-)(aq), K_(a)=1.6 xx 10^(-7)),(HCl(g)+aq rarr H^(+) (aq) + Cl^(-)(aq), K_(a) = 1 xx 10^(10)):}` Since the ELECTRONEGATIVITY decreases in the order : `Cl gt S gt P`, therefore, stability of the conjugate bases decreases in the same order, i.e., `Cl^(-) gt HS^(-) gt H_(2)P^(-)`, In other words, acidity of the corresponding acids decreases in the same order, i.e., `HCl gt H_(2)S gt PH_(3)`. |
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