Chemistry · Textbook solutions

Redox Reactions

Every solved example, exercise, and miscellaneous question — in the order the textbook teaches them. · 36 questions

6. Redox Reactions — worked examples

9 q

Solved Examples

Worked · 9
  1. Solved Ex.6.1
    Deduce the oxidation number of S in the following species: i. SO2\mathrm{SO_2} ii. SO42⊖\mathrm{SO_4^{2\ominus}}
  2. Solved Ex.6.2
    Assign oxidation number to each element in the following compounds or ions. a. KMnO4\mathrm{KMnO_4} b. K2Cr2O7\mathrm{K_2Cr_2O_7} c. Ca3(PO4)2\mathrm{Ca_3(PO_4)_2}
  3. Solved Ex.6.3
    Assign oxidation number to the atoms other than O and H in the following species. i. SO32⊖\mathrm{SO_3^{2\ominus}} ii. BrO3⊖\mathrm{BrO_3^{\ominus}} iii. ClO4⊖\mathrm{ClO_4^{\ominus}} iv. NH4⊕\mathrm{NH_4^{\oplus}} v. NO3⊖\mathrm{NO_3^{\ominus}} vi. NO2⊖\mathrm{NO_2^{\ominus}} vii. SO3\mathrm{SO_3} viii. N2O5\mathrm{N_2O_5}
  4. Solved Ex.6.4
    Identify whether the following reactions are redox or not. State oxidants and reductants therein. a. 3H3AsO3(aq)+BrO3⊖(aq)⟶Br⊖(aq)+3H3AsO4(aq)\mathrm{3H_3AsO_3(aq) + BrO_3^{\ominus}(aq) \longrightarrow Br^{\ominus}(aq) + 3H_3AsO_4(aq)}
  5. Solved Ex.6.5
    Using the oxidation number method write the net ionic eqvation for the reaction of potassium permanganate, KMnO4\mathrm{KMnO_4}, with ferrous sulphate, FeSO4\mathrm{FeSO_4}. MnO4⊖(aq)+Fe2⊕(aq)⟶Mn2⊕(aq)+Fe3⊕(aq)\mathrm{MnO_4^{\ominus}(aq) + Fe^{2\oplus}(aq) \longrightarrow Mn^{2\oplus}(aq) + Fe^{3\oplus}(aq)}
  6. Solved Ex.6.6
    Balance the following reaction by oxidation number mathod. CuO+NH3⟶Cu+N2+H2O\mathrm{CuO + NH_3 \longrightarrow Cu + N_2 + H_2O}
  7. Solved Ex.6.7
    Balance the following unbalanced equation (in acidic medium) by ion electron (half reaction method) Mn2⊕(aq)+ClO3⊖(aq)⟶MnO2(s)+ClO2(aq)\mathrm{Mn^{2\oplus}(aq) + ClO_3^{\ominus}(aq) \longrightarrow MnO_2(s) + ClO_2(aq)}
  8. Solved Ex.6.8
    Balance the following unbalanced equation by ion electron (half reaction method) H2O2(aq)+ClO4⊖(aq)⟶ClO2⊖(aq)+O2(g)\mathrm{H_2O_2(aq) + ClO_4^{\ominus}(aq) \longrightarrow ClO_2^{\ominus}(aq) + O_2(g)}
  9. Solved Ex.6.9
    By using standard electrode potential table justify that the reaction between the following is spontaneous. (a) Fe3⊕(aq)\mathrm{Fe^{3\oplus}(aq)} and I⊖(aq)\mathrm{I^{\ominus}(aq)} (b) Ag⊕(aq)\mathrm{Ag^{\oplus}(aq)} and Cu(s)\mathrm{Cu(s)}

Exercises

27 q

1. Choose the most correct option

Practice · 10
  1. Choose the most correct option
    Ex Q.1 (A)
    Oxidation numbers of Cl atoms marked as Cla\mathrm{Cl^a} and Clb\mathrm{Cl^b} in CaOCl2\mathrm{CaOCl_2} (bleaching powder) are Cla−Ca−O−Clb\mathrm{Cl^a - Ca - O - Cl^b}
    1. A.
      zero in each
    2. B.
      −1-1 in Cla\mathrm{Cl^a} and +1+1 in Clb\mathrm{Cl^b}
    3. C.
      +1+1 in Cla\mathrm{Cl^a} and −1-1 in Clb\mathrm{Cl^b}
    4. D.
      1 in each
  2. Ex Q.1 (B)
    Which of the following is not an example of redox reacton ?
    1. A.
      CuO+H2⟶Cu+H2O\mathrm{CuO + H_2 \longrightarrow Cu + H_2O}
    2. B.
      Fe2O3+3CO2⟶2Fe+3CO2\mathrm{Fe_2O_3 + 3CO_2 \longrightarrow 2Fe + 3CO_2}
    3. C.
      2K+F2⟶2KF\mathrm{2K + F_2 \longrightarrow 2KF}
    4. D.
      BaCl2+H2SO4⟶BaSO4+2HCl\mathrm{BaCl_2 + H_2SO_4 \longrightarrow BaSO_4 + 2HCl}
  3. Ex Q.1 (C)
    A compound contains atoms of three elements A, B and C. If the oxidation state of A is +2+2, B is +5+5 and that of C is −2-2, the compound is possibly represented by
    1. A.
      A2(BC3)2\mathrm{A_2(BC_3)_2}
    2. B.
      A3(BC4)2\mathrm{A_3(BC_4)_2}
    3. C.
      A3(B4C)2\mathrm{A_3(B_4C)_2}
    4. D.
      ABC2\mathrm{ABC_2}
  4. Ex Q.1 (D)
    The coefficients p, q, r, s in the reaction p Cr2O72⊖+q Fe2⊕⟶r Cr3⊕+s Fe3⊕+H2O\mathrm{p\ Cr_2O_7^{2\ominus} + q\ Fe^{2\oplus} \longrightarrow r\ Cr^{3\oplus} + s\ Fe^{3\oplus} + H_2O} respectively are :
    1. A.
      1, 2, 6, 6
    2. B.
      6, 1, 2, 4
    3. C.
      1, 6, 2, 6
    4. D.
      1, 2, 4, 6
  5. Ex Q.1 (E)
    For the following redox reactions, find the correct statement. Sn2⊕+2Fe3⊕⟶Sn4⊕+2Fe2⊕\mathrm{Sn^{2\oplus} + 2Fe^{3\oplus} \longrightarrow Sn^{4\oplus} + 2Fe^{2\oplus}}
    1. A.
      Sn2⊕\mathrm{Sn^{2\oplus}} is undergoing oxidation
    2. B.
      Fe3⊕\mathrm{Fe^{3\oplus}} is undergoing oxidation
    3. C.
      It is not a redox reaction
    4. D.
      Both Sn2⊕\mathrm{Sn^{2\oplus}} and Fe3⊕\mathrm{Fe^{3\oplus}} are oxidised
  6. Ex Q.1 (F)
    Oxidation number of carbon in H2CO3\mathrm{H_2CO_3} is
    1. A.
      +1+1
    2. B.
      +2+2
    3. C.
      +3+3
    4. D.
      +4+4
  7. Ex Q.1 (G)
    Which is the correct stock notation for magenese dioxide ?
    1. A.
      Mn(I)O2\mathrm{Mn(I)O_2}
    2. B.
      Mn(II)O2\mathrm{Mn(II)O_2}
    3. C.
      Mn(III)O2\mathrm{Mn(III)O_2}
    4. D.
      Mn(IV)O2\mathrm{Mn(IV)O_2}
  8. Ex Q.1 (I)
    Oxidation number of oxygen in superoxide is
    1. A.
      −2-2
    2. B.
      −1-1
    3. C.
      −12-\dfrac{1}{2}
    4. D.
      00
  9. Ex Q.1 (J)
    Which of the following halogens does always show oxidation state −1-1 ?
    1. A.
      F\mathrm{F}
    2. B.
      Cl\mathrm{Cl}
    3. C.
      Br\mathrm{Br}
    4. D.
      I\mathrm{I}
  10. Ex Q.1 (K)
    The process SO2⟶S2Cl2\mathrm{SO_2 \longrightarrow S_2Cl_2} is
    1. A.
      Reduction
    2. B.
      Oxidation
    3. C.
      Neither oxidation nor reduction
    4. D.
      Oxidation and reduction.

2. Write the formula for the following compounds

Practice · 4
  1. Write the formula for the following compounds :
    Ex Q.2 (A)
    Mercury(II) chloride
  2. Ex Q.2 (B)
    Thallium(I) sulphate
  3. Ex Q.2 (C)
    Tin(IV) oxide
  4. Ex Q.2 (D)
    Chromium(III) oxide

3. Answer the following questions

Practice · 10
  1. Answer the following questions
    Ex Q.3 (A)
    In which chemical reaction does carbon exibit variation of oxidation state from −4-4 to +4+4 ? Write balanced chemical reaction.
  2. Ex Q.3 (B)
    In which reaction does nitrogen exhibit variation of oxidation state from −3-3 to +5+5 ?
  3. Ex Q.3 (C)
    Calculate the oxidation number of underlined atoms. a. H2S‾O4\mathrm{H_2\underline{S}O_4} b. HN‾O3\mathrm{H\underline{N}O_3} c. H3P‾O3\mathrm{H_3\underline{P}O_3} d. K2C‾2O4\mathrm{K_2\underline{C}_2O_4} e. H2S‾4O6\mathrm{H_2\underline{S}_4O_6} f. Cr‾2O72−\underline{\mathrm{Cr}}_2\mathrm{O_7^{2-}} g. NaH2P‾O4\mathrm{NaH_2\underline{P}O_4}
  4. Ex Q.3 (D)
    Justify that the following reactions are redox reaction; identify the species oxidized/reduced, which acts as an oxidant and which act as a reductant. a. 2Cu2O(s)+Cu2S(s)⟶6Cu(s)+SO2(g)\mathrm{2Cu_2O(s) + Cu_2S(s) \longrightarrow 6Cu(s) + SO_2(g)} b. HF(aq)+OH⊖(aq)⟶H2O(l)+F⊖(aq)\mathrm{HF(aq) + OH^{\ominus}(aq) \longrightarrow H_2O}(l) + \mathrm{F^{\ominus}(aq)} c. I2(aq)+2S2O32⊖(aq)⟶S4O62⊖(aq)+2I⊖(aq)\mathrm{I_2(aq) + 2S_2O_3^{2\ominus}(aq) \longrightarrow S_4O_6^{2\ominus}(aq) + 2I^{\ominus}(aq)}
  5. Ex Q.3 (E)
    What is oxidation? Which one of the following pairs of species is in its oxidized state ? a. Mg/Mg2⊕\mathrm{Mg / Mg^{2\oplus}} b. Cu/Cu2⊕\mathrm{Cu / Cu^{2\oplus}} c. O2/O2⊖\mathrm{O_2 / O^{2\ominus}} d. Cl2/Cl⊖\mathrm{Cl_2 / Cl^{\ominus}}
  6. Ex Q.3 (F)
    Justify the following reaction as redox reaction. 2Na(s)+S(s)⟶Na2S(s)\mathrm{2Na(s) + S(s) \longrightarrow Na_2S(s)} Find out the oxidizing and reducing agents.
  7. Ex Q.3 (G)
    Provide the stock notation for the following compounds : HAuCl4\mathrm{HAuCl_4}, Tl2O\mathrm{Tl_2O}, FeO\mathrm{FeO}, Fe2O3\mathrm{Fe_2O_3}, MnO\mathrm{MnO} and CuO\mathrm{CuO}.
  8. Ex Q.3 (H)
    Assign oxidation number to each atom in the following species. a. Cr(OH)4⊖\mathrm{Cr(OH)_4^{\ominus}} b. Na2S2O3\mathrm{Na_2S_2O_3} c. H3BO3\mathrm{H_3BO_3}
  9. Ex Q.3 (I)
    Which of the following redox couple is stronger oxidizing agent ? a. Cl2\mathrm{Cl_2} (E0=1.36 V)(\mathrm{E^0} = 1.36\ \mathrm{V}) and Br2\mathrm{Br_2} (E0=1.09 V)(\mathrm{E^0} = 1.09\ \mathrm{V}) b. MnO4⊖\mathrm{MnO_4^{\ominus}} (E0=1.51 V)(\mathrm{E^0} = 1.51\ \mathrm{V}) and Cr2O72⊖\mathrm{Cr_2O_7^{2\ominus}} (E0=1.33 V)(\mathrm{E^0} = 1.33\ \mathrm{V})
  10. Ex Q.3 (J)
    Which of the following redox couple is stronger reducing agent ? a. Li\mathrm{Li} (E0=−3.05 V)(\mathrm{E^0} = -3.05\ \mathrm{V}) and Mg\mathrm{Mg} (E0=−2.36 V)(\mathrm{E^0} = -2.36\ \mathrm{V}) b. Zn\mathrm{Zn} (E0=−0.76 V)(\mathrm{E^0} = -0.76\ \mathrm{V}) and Fe\mathrm{Fe} (E0=−0.44 V)(\mathrm{E^0} = -0.44\ \mathrm{V})

4. Balance the reactions/equations

Practice · 2
  1. Balance the reactions/equations :
    Ex Q.4 (A)
    Balance the following reactions by oxidation number method a. Cr2O72⊖(aq)+SO32⊖(aq)⟶Cr3⊕(aq)+SO42⊖(aq)\mathrm{Cr_2O_7^{2\ominus}(aq) + SO_3^{2\ominus}(aq) \longrightarrow Cr^{3\oplus}(aq) + SO_4^{2\ominus}(aq)} (acidic) b. MnO4⊖(aq)+Br⊖(aq)⟶MnO2(s)+BrO3⊖(aq)\mathrm{MnO_4^{\ominus}(aq) + Br^{\ominus}(aq) \longrightarrow MnO_2(s) + BrO_3^{\ominus}(aq)} (basic) c. H2SO4(aq)+C(s)⟶CO2(g)+SO2(g)+H2O(l)\mathrm{H_2SO_4(aq) + C(s) \longrightarrow CO_2(g) + SO_2(g) + H_2O}(l) (acidic) d. Bi(OH)3(g)+Sn(OH)3⊖(aq)⟶Bi(s)+Sn(OH)62⊖(aq)\mathrm{Bi(OH)_3(g) + Sn(OH)_3^{\ominus}(aq) \longrightarrow Bi(s) + Sn(OH)_6^{2\ominus}(aq)} (basic)
  2. Ex Q.4 (B)
    Balance the following redox equation by half reaction method a. H2C2O4(aq)+MnO4⊖(aq)⟶CO2(g)+Mn2⊕(aq)\mathrm{H_2C_2O_4(aq) + MnO_4^{\ominus}(aq) \longrightarrow CO_2(g) + Mn^{2\oplus}(aq)} (acidic) b. Bi(OH)3(s)+SnO22⊖(aq)⟶SnO32⊖(aq)+Bi(s)\mathrm{Bi(OH)_3(s) + SnO_2^{2\ominus}(aq) \longrightarrow SnO_3^{2\ominus}(aq) + Bi(s)} (basic)

5. Complete the following table

Practice · 1
  1. Complete the following table :
    Ex Q.5
    Assign oxidation number to the underlined species and write Stock notation of compound
    CompoundOxidation numberStock notation
    Au‾Cl3\underline{\mathrm{Au}}\mathrm{Cl_3}
    Sn‾Cl2\underline{\mathrm{Sn}}\mathrm{Cl_2}
    V‾2O74⊖\underline{\mathrm{V}}_2\mathrm{O_7^{4\ominus}}
    Pt‾Cl62⊖\underline{\mathrm{Pt}}\mathrm{Cl_6^{2\ominus}}
    H3As‾O3\mathrm{H_3}\underline{\mathrm{As}}\mathrm{O_3}