4.7Since the pKaof HCN is given as 9.1, its Ka109.1. In more conventional notation, Ka81010. Hydrogen cyanide is a weak acid.4.8Hydrogen cyanide is a weak acid, but it is a stronger acid than water (pKa15.7). Since HCN is astronger acid than water, its conjugate base (CN) is a weaker base than hydroxide (HO), which isthe conjugate base of water.4.9An unshared electron pair on oxygen abstracts the proton from hydrogen chloride.4.10In any proton-transfer process, the position of equilibrium favors formation of the weaker acid andthe weaker base from the stronger acid and base. Alkyloxonium ions (ROH2) have approximatelythe same acidity as hydronium ion (H3O , pKa1.7). Thus hydrogen chloride (pKa7) is thestronger acid. tert-Butyl alcohol is the stronger base because it is the conjugate of the weaker acid(tert-butyloxonium ion).The equilibrium constant for proton transfer from hydrogen chloride to tert-butyl alcohol is muchgreater than 1.4.11The proton being transferred is partially bonded to the oxygen of tert-butyl alcohol and to chloride
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