Assign appropriate reasons for each of the following statements.
(i)More metal fluorides are ionic in nature than metal chlorides.
(ii) Hydrogen fluoride is a weaker acid than hydrogen chloride in aqueous solution.
(iii)In aqueous solution HI is a stronger acid than HCI ?
(iv) Addition of `Cl_(2)` to KI solution gives it a brown colour but excess of `Cl_(2)` turns it colourless.
(v) Perchloric acid is a stronger acid than sulphuric acid.

Answer

(i)According to Fajan rules, a bigger anion is more easily polarized than a smaller anion. Thus, the same metal cation can polarize bigger `Cl^(-)` ion more easily than the smaller `F^(-)` ion.In other words, for the same metal, the metal fluoride is more ionic than metal chloride.Therefore, in general, we can easily say that more metal fluorides are ionic than metal chlorides.
(ii)Because of smaller size of `F` as compared to `Cl`, the bond dissociation energy of `H-F` bond is much higher than that of `H-CI` bond.As a result, in aqueous solution, `H-Cl`, the bond can break more easily to form `H^(+)` ion than `H-F` bond.Thus, hydrogen fluoride is a weaker acid than hydrogen chloride in aqueous solution.
(iii)Due to smaller size of `Cl` as compared to `l`, bond dissociation energy of `H-Cl` bond is much higher than that of `H-l` bond.As a result, in aqueous solution `H-i` bond breaks more easily to release `H^(+)` ion than `H-Cl` bond.Thus, `Hl` is a stronger acid than `HCl` in aqueous solution.
(iv)`Cl_(2)` being a stronger oxidising agent than `l_(2)`, first oxidises `Kl` to give `l_(2)` which imparts brown colour to the solution.
`2Kl (aq)+ Cl_(2) (g)to2 KCl (aq) + underset("Brown")(l_(2) (s))`
If, however, `Cl_(2)` is passed in excess, the `l_(2)` thus formed gets further oxidized to iodic acid `(HIO_(3))` which is colourless.
`5 Cl_(2) + l_(2) + 6 H_(2)Oto10 HCl +2 underset("Colourless")(HIO_(3))`
(v)The oxidation state of `Cl` in perchloric acid is `+7` while that of `S` in sulphuric acid is `+6`
`(##RES_INO_CHM_XII_V02_C03_E01_020_A01##)`
Due to higher oxidation state and higher electronegativity of `CI, CIO_(3)` part of `HCIO_(4)` pullls the electrons of the `O-H` bond more strongly and hence can break the `O-H` bond more easily to liberate a proton than `SO_(2)` part in `H_(2)SO_(4)`.Thus, perchloric acid is stronger acid than sulphuric acid.