JEE Advanced 2017 Paper 1 · Chemistry · s-Block, p-Block Elements and Hydrogen · medium
Halogens and their oxo-compounds undergo several redox reactions.
One or more options correct
Halogens and their oxo-compounds undergo several redox reactions. The CORRECT statement(s) is/are
A.Passing 0.30 mol of Cl2 into hot concentrated NaOH forms 0.50 mol of NaCl together with 0.10 mol of NaClO3.
B.Chlorine passed into cold dilute NaOH gives NaCl and NaOCl, in which the oxidation state of chlorine in the oxo-anion is +1.
C.Iodine is oxidised by concentrated HNO3 to iodic acid, 10 mol of electrons being lost per mole of I2.
D.Fluorine reacts with cold dilute NaOH to give NaFO, in exact analogy with chlorine.
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Answer:A, B, C
(A) Hot concentrated alkali makes chlorine disproportionate: 3Cl2+6NaOH→5NaCl+NaClO3+3H2O. Thus 0.30 mol Cl2 gives 0.50 mol NaCl and 0.10 mol NaClO3: correct. (B) In the cold, the reaction stops at hypochlorite, Cl2+2NaOH→NaCl+NaOCl+H2O, and chlorine in OCl− is +1 (x−2=−1): correct. (C) I2+10HNO3→2HIO3+10NO2+4H2O: each iodine goes from 0 to +5, so each I2 loses 2×5=10 electrons: correct. (D) Fluorine is the most electronegative element and cannot show a positive oxidation state in any oxo-anion; with dilute alkali it forms OF2 (and NaF), and with concentrated alkali O2. No NaFO is formed: wrong.