REDOX REACTIONSTIONSTIONSTIONS

1 Of the following is not an example of REDOX reaction?(i)CuO + H2 Cu + H2O(ii)Fe2O3 + 3CO 2Fe + 3CO2(iii)2K + F2 2KF(iv)BaCl2 + H2SO4 BaSO4 + more positive the value of EV, the greater is the tendency of the species toget reduced. Using the standard electrode potential of REDOX couples givenbelow find out which of the following is the strongest oxidising values: Fe3+/Fe2+ = + ; I2(s)/I = + ; Cu2+/Cu = + ; Ag+/Ag = + (i)Fe3+(ii)I2(s)(iii)Cu2+(iv)Ag+ values of some REDOX couples are given below. On the basis of these valueschoose the correct values : Br2/Br = + ; Ag+ /Ag(s) = + Cu2+/Cu(s) = + ; I2(s)/I = + (i)Cu will reduce Br (ii)Cu will reduce Ag(iii)Cu will reduce I (iv)Cu will reduce Br2I. Multiple Choice Questions (Type-I)UnitUnitUnitUnitUnit88 REDOX REACREDOX REACREDOX REACREDOX REACREDOX REACTIONSTIONSTIONSTIONSTIONSREDOX REACREDOX REACREDOX REACREDOX REACREDOX the standard electrode potential, find out the pair between which redoxreaction is not values : Fe3+/Fe2+ = + ; I2/I = + ; Cu2+/Cu = + ; Ag+/Ag = + V(i)Fe3+ and I (ii)Ag+ and Cu(iii)Fe3+ and Cu(iv)Ag and Fe3+ reacts differently with iodine and bromine in the reactions givenbelow:2S2O32 + I2 S4O62 + 2I S2O32 + 2Br2 + 5H2O 2SO42 + 2Br + 10 H+Which of the following statements justifies the above dual behaviour ofthiosulphate?

2 (i)Bromine is a stronger oxidant than iodine.(ii)Bromine is a weaker oxidant than iodine.(iii)Thiosulphate undergoes oxidation by bromine and reduction by iodinein these reactions.(iv)Bromine undergoes oxidation and iodine undergoes reduction in oxidation number of an element in a compound is evaluated on the basisof certain rules. Which of the following rules is not correct in this respect?(i)The oxidation number of hydrogen is always +1.(ii)The algebraic sum of all the oxidation numbers in a compound is zero.(iii)An element in the free or the uncombined state bears oxidationnumber zero.(iv)In all its compounds, the oxidation number of fluorine is which of the following compounds, an element exhibits two differentoxidation states.(i)NH2OH(ii)NH4NO3(iii)N2H4(iv) of the following arrangements represent increasing oxidation numberof the central atom?

3 (i)CrO2 , ClO3 , CrO42 , MnO4 (ii)ClO3 , CrO42 , MnO4 , CrO2 105 REDOX Reactions16-04-2018106 Exemplar Problems, Chemistry(iii)CrO2 , ClO3 , MnO4 , CrO42 (iv)CrO42 , MnO4 , CrO2 , ClO3 largest oxidation number exhibited by an element depends on its outerelectronic configuration. With which of the following outer electronicconfigurations the element will exhibit largest oxidation number?(i)3d14s2(ii)3d34s2(iii)3d54s1(iv ) disproportionation reaction(i)CH4 + 2O2 CO2 + 2H2O(ii)CH4 + 4Cl2 CCl4 + 4 HCl(iii)2F2 + 2OH 2F + OF2 + H2O(iv)2NO2 + 2OH NO2 + NO3 + of the following elements does not show disproportionation tendency?(i)Cl(ii)Br(iii)F(iv)III. Multiple Choice Questions (Type-II)In the following questions two or more options may be of the following statement(s) is/are not true about the followingdecomposition 2 KCl + 3O2(i)Potassium is undergoing oxidation(ii)Chlorine is undergoing oxidation(iii)Oxygen is reduced(iv)None of the species are undergoing oxidation or the correct statement (s) in relation to the following reaction:Zn + 2 HCl ZnCl2 + H2(i)Zinc is acting as an oxidant(ii)Chlorine is acting as a reductant(iii)Hydrogen ion is acting as an oxidant(iv)Zinc is acting as a reductant16-04-2018107 REDOX exhibition of various oxidation states by an element is also related to theouter orbital electronic configuration of its atom.

4 Atom(s) having which of thefollowing outermost electronic configurations will exhibit more than one oxidationstate in its compounds.(i)3s1(ii)3d14s2(iii)3d24s2(iv ) the correct statements with reference to the given reactionP4 + 3OH + 3H2O PH3 + 3H2PO2 (i)Phosphorus is undergoing reduction only.(ii)Phosphorus is undergoing oxidation only.(iii)Phosphorus is undergoing oxidation as well as reduction.(iv)Hydrogen is undergoing neither oxidation nor of the following electrodes will act as anodes, when connected toStandard Hydrogen Electrode?(i)Al/Al3+EV = (ii)Fe/Fe2+EV = (iii)Cu/Cu2+EV = + (iv)F2 (g)/2F (aq)EV = + Short Answer reactionCl2 (g) + 2OH (aq) ClO (aq) + Cl (aq) + H2O (l)represents the process of bleaching. Identify and name the species thatbleaches the substances due to its oxidising 4 MnO undergoes disproportionation reaction in acidic medium but MnO4 does not.

5 Give and PbO2 react with HCl according to following chemical equations :2 PbO + 4 HCl 2 PbCl2 + 2H2 OPbO2 + 4 HCl PbCl2 + Cl2 + 2H2 OWhy do these compounds differ in their reactivity? acid is an oxidising agent and reacts with PbO but it does not reactwith PbO2. Explain why?16-04-2018108 Exemplar Problems, balanced chemical equation for the following reactions:(i)Permanganate ion (MnO4 ) reacts with sulphur dioxide gas in acidicmedium to produce Mn2+ and hydrogensulphate ion.(Balance by ion electron method)(ii)Reaction of liquid hydrazine (N2H4) with chlorate ion (ClO3 ) in basicmedium produces nitric oxide gas and chloride ion in gaseous state.(Balance by oxidation number method)(iii)Dichlorine heptaoxide (Cl2O7) in gaseous state combines with an aqueoussolution of hydrogen peroxide in acidic medium to give chlorite ion(ClO2 ) and oxygen gas.

6 (Balance by ion electron method) the oxidation number of phosphorus in the following species.(a) 2 3 HPO and(b) 3 the oxidation number of each sulphur atom in the followingcompounds:(a) Na2S2O3(b) Na2S4O6(c) Na2SO3 (d) the following equations by the oxidation number method.(i)Fe2+ + H+ + Cr22 7O Cr3+ + Fe3+ + H2O(ii)I2 + N 3O NO2 + I 3O(iii)I2 + S22 3O I + S42 6O(iv)MnO2 + C22 4O Mn2+ + the REDOX reactions out of the following reactions and identify theoxidising and reducing agents in them.(i)3 HCl(aq) + HNO3 (aq) Cl2 (g) + NOCl (g) + 2H2O (l)(ii)HgCl2 (aq) + 2KI (aq) HgI2 (s) + 2 KCl (aq)(iii)Fe2O3 (s) + 3CO (g) 2Fe (s) + 3CO2 (g)(iv)PCl3 (l) + 3H2O (l) 3 HCl (aq) + H3 PO3 (aq)(v)4NH3 + 3O2 (g) 2N2 (g) + 6H2O (g) the following ionic equations (i)Cr22 7O + H+ + I Cr3+ + I2 + H2O(ii)Cr22 7O + Fe2+ + H+ Cr3+ + Fe3+ + H2O(iii)Mn 4O + S2 3O + H+ Mn2+ + S2 4O + H2O(iv)Mn 4O + H+ + Br Mn2+ + Br2 + H2O16-04-2018109 REDOX ReactionsIV.

7 Matching Column I with Column II for the oxidation states of the central IColumn II(i)Cr2O72 (a)+ 3(ii)MnO4 (b)+ 4(iii)VO3 (c)+ 5(iv)FeF63 (d)+ 6(e)+ the items in Column I with relevant items in Column IColumn II(i)Ions having positive charge(a)+7(ii)The sum of oxidation number(b) 1of all atoms in a neutral molecule(c)+1(iii)Oxidation number of hydrogen ion (H+)(d)0(iv)Oxidation number of fluorine in NaF(e)Cation(v)Ions having negative charge(f)AnionV. Assertion and Reason TypeIn the following questions a statement of assertion (A) followed by a statementof reason (R) is given. Choose the correct option out of the choices givenbelow each (A) :Among halogens fluorine is the best (R) :Fluorine is the most electronegative atom.(i)Both A and R are true and R is the correct explanation of A.(ii)Both A and R are true but R is not the correct explanation of A.

8 (iii)A is true but R is false.(iv)Both A and R are (A):In the reaction between potassium permanganate andpotassium iodide, permanganate ions act as oxidising (R) :Oxidation state of manganese changes from +2 to +7 duringthe reaction.(i)Both A and R are true and R is the correct explanation of A.(ii)Both A and R are true but R is not the correct explanation of A.(iii)A is true but R is false.(iv)Both A and R are Problems, (A) :The decomposition of hydrogen peroxide to form water andoxygen is an example of disproportionation (R) :The oxygen of peroxide is in 1 oxidation state and it isconverted to zero oxidation state in O2 and 2 oxidation statein H2O.(i)Both A and R are true and R is the correct explanation of A.(ii)Both A and R are true but R is not the correct explanation of A.

9 (iii)A is true but R is false.(iv)Both A and R are (A) : REDOX couple is the combination of oxidised and reducedform of a substance involved in an oxidation or reductionhalf (R) :In the representation ++32Fe/FeEV and +2Cu/CuEV, Fe3+/ Fe2+and Cu2+ / Cu are REDOX couples.(i)Both A and R are true and R is the correct explanation of A.(ii)Both A and R are true but R is not the correct explanation of A.(iii)A is true but R is false.(iv)Both A and R are Long Answer REDOX reactions on the basis of electron transfer. Give suitable the basis of standard electrode potential values, suggest which of thefollowing reactions would take place? (Consult the book for EV value).(i)Cu + Zn2+ Cu2+ + Zn(ii)Mg + Fe2+ Mg2+ + Fe(iii)Br2 + 2Cl Cl2 + 2Br (iv)Fe + Cd2+ Cd + Fe2+ does fluorine not show disporportionation reaction?

10 REDOX couples involved in the reactions (i) to (iv) given in question out the oxidation number of chlorine in the following compounds andarrange them in increasing order of oxidation number of , NaClO3, NaClO, KClO2, Cl2O7, ClO3, Cl2O, NaCl, Cl2, oxidation state is not present in any of the above compounds? method can be used to find out strength of reductant/oxidant in asolution? Explain with an ReactionsANSWERSI. Multiple Choice Questions (Type-I)1. (iv)2. (iv)3. (iv)4. (iv)5. (i)6. (i)7. (ii)8. (i)9. (iv)10. (iv)11. (iii)II. Multiple Choice Questions (Type-II)12. (i), (iv)13. (iii), (iv)14. (iii), (iv)15. (iii), (iv)16. (i), (ii)III. Short Answer 4 MnO, Mn is in the highest oxidation state +7. Therefore, it doesnot undergo disproportionation. MnO42 undergoes disproportionationas follows :3 MnO42 + 4H+ 2 MnO4 + MnO2 + + 4 HCl 2 PbCl2 + 2H2O (Acid base reaction)PbO2 + 4 HCl PbCl2 + Cl2 + 2H2O ( REDOX reaction)(Hint : Note the oxidation number of lead in the oxides) is a basic oxide and simple acid base reaction takes place betweenPbO and HNO3.