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Assign reasons for the following : (i) When a moist blue litmus paper is dipped in a solution of hypochlorous acid, it first turns red and then latter gets decolourised. Explain. (ii) Iodine is liberated when KI is added to a solution of Cu^(2+) ions but Cl_(2) is not liberated when KCI is added to a solution of Cu^(2+) ions. Why ? (iii) Na_(2)S_(2)O_(3) reacts with Cl_(2) and I_(2) to give different oxidation products. Write the equations of the reactions involved and give a plausible explanation of their contrasting behaviour. (iv) Name a compound of fluorine which shows +1 oxidation state. How is this compound prepared ? Is this a disproportionation reaction ? |
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Answer» Solution :(i) HOCl acts as an acid and hence turns blue litmus red. `HOCl rarr H^(+) OCl^(-)` It also works ASA bleaching AGENT, and thus decolourises red litmus by nascent oxygen. `HOCl rarr HCl + [O]` (ii) The `I^(-)` ion being a strong reduucing agent reduces `Cu^(2+)` to `Cu^(+)` and itself gets oxidised to `I_(2)` `2 Cu^(2+) + 4 KI rarr Cu_(2)I_(2) + I_(2) + 4 K^(+)` Since `Cl^(-)` ion does not act as a reducing agent, therefore, `Cl_(2)` is not liberated when KCl is added to a solution of `Cu^(2+)` ions. (iii) `Cl_(2)` is a stronger oxidising agent than `I_(2)` and hence oxidises `Na_(2)S_(2)O_(3)` to `NaHSO_(4)` in which the oxidation state of S increase from +2 to +6 while with `I_(2)` only sodium tetrathionate is obtained in which the oxidation state of S increases from + 2 to + 2.5 only. `{:(Na_(2)overset(+2)(S_(2))O_(3)+4Cl_(2) + 5H_(2)O rarr 2 Na overset(+6)(HSO_(4))+8HCl),(""Na_(2)overset(+2)(S_(2))O_(3)+I_(2)rarr 2 NaI + underset("Sod. tetrathionate")(Na_(2)overset(+2.5)(S_(4))O_(6))):}` (iv) The compound of F which SHOWS an oxidation state of +1 is HOF. It is prepared by passing `F_(2)` over ice at 233 K. `overset(0)(F_(2))+H_(2)O(ice) overset(23 K)hArr overset(+1)(HOF)+overset(-1)(HF)` This is a disproportionation reaction since the oxidation state of F decreases from zero in `F_(2)` to -1 in HF and increases to +1 in HOF. |
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