Redox Reaction and Equivalent Concept Exercise # 1

REDOX REACTION AND EQUIVALENT CONCEPT Exercise # 1 [Single Correct Choice Type Questions] 1. Which reaction does not represent autoredox or disproportionation :(A) Cl2 + OH–  Cl– + ClO3– + H2O (B) 2H2O2  H2O + O2 (C) 2Cu+  Cu+2 + Cu (D) (NH4)2Cr2O7  N2 + Cr2O3 + 4H2O 2. Match List-I (Compounds) with List-II (Oxidation states of nitrogen) and select answer using the codes given below the lists :List-I List-II (A) NaN3 1. +5 (B) N2H2 2. +2 (C) NO 3. –1/3 (D) N2O5 4. –1 Code : (A) (B) (C) (D) (A) 3 4 2 1 (B) 4 3 2 1 (C) 3 4 1 2 (D) 4 3 1 2 3. Which of the following is a redox reaction :(A) 2 CrO42– + 2H+  Cr2O72– + H2O (B) CuSO4 + 4 NH3  [Cu(NH3)4] SO4 (C) Na2S2O3 + I2  Na2S4O6 + NaI (D) Cr2O72– + 2OH–  2 CrO42– + H2O 4. 50 mL of 0.1 M solution of a salt reacted with 25 mL of 0.1 M solution of sodium sulphite. The half reaction for the oxidation of sulphite ion is :+ – SO32– (aq) + H2O ()  SO 2– 4 (aq) + 2H (aq) + 2e If the oxidation number of metal in the salt was 3, what would be the new oxidation number of metal : (A) zero (B) 1 (C) 2 (D) 4 5. An element A in a compound ABD has oxidation number An–. It is oxidised by Cr2O72– in acid medium. In the experiment 1.68 × 10–3 moles of K2Cr2O7 were used for 3.26 × 10–3 moles of ABD. The new oxidation number of A after oxidation is (A) 3 (B) 3 – n (C) n – 3 (D) +n 6. The incorrect order of decreasing oxidation number of S in compounds is :(A) H2S2O7 > Na2S4O6 > Na2S2O3 > S8 (B) H2SO5 > H2SO3 > SCl2 > H2S (C) SO3 > SO2 > H2S > S8 (D) H2SO4 > SO2 > H2S > H2S2O8 7. In which of the following reaction is there a change in the oxidation number of nitrogen atoms :(A) 2 NO2  N2O4 (B) NH3 + H2O  NH4+ + OH– (C) N2O5 + H2O  2HNO3 (D) none 8. In the reaction xHI + yHNO3 NO + I2 + H2O (A) x = 3, y = 2 (B) x = 2, y = 3 9. (C) x = 6, y = 2 For the redox reaction : MnO4– + C2O42– + H+ Mn2+ + CO2 + H2O the correct stoichiometric coefficients of MnO4–, C2O42– and H+ are respectively (A) 2,5,16 (B) 16,5,2 (C) 5,16,2 (D) x = 6, y = 1 (D) 2,16,5 10. A certain weight of pure CaCO3 is made to react completely with 200 mL of an HCl solution to give 224 mL of CO2 gas at STP. The normality of the HCl is :(A) 0.05 N (B) 0.1 N (C) 1.0 N (D) 0.2 N 11. The volume of 1.5 MH3PO4 solution required to neutralize exactly 90 mL of a 0.5 M Ba (OH)2 solution is :(A) 10 mL (B) 30 mL (C) 20 mL (D) 60 mL 12. Volume V1 mL of 0.1 MK2Cr2O7 is needed for complete oxidation of 0.678 g N2H4 in acidic medium. The volume of 0.3 M KMnO4 needed for same oxidation in acidic medium will be :2 5 (A) V1 (B) V1 (C) 113 V1 (D) can't say 5 2 13. Which of the following relations is incorrect :(A) 3 N Al2 (SO4)3 = 0.5 M Al2 (SO4)3 (C) 1 M H3PO4 = 1/3 N H3PO4 (B) 3 M H2SO4 = 6 N H2 SO4 (D) 1 M Al2 (SO4)3 = 6 N Al2(SO4)3 14. The mass of oxalic acid crystals (H2C2O4. 2H2O) required to prepare 50 mL of a 0.2 N solution is :(A) 4.5 g (B) 6.3 g (C) 0.63 g (D) 0.45 g 15. 125 mL of 63% (w/v) H2C2O4. 2H2O is made to react with 125 mL of a 40% (w/v) NaOH solution. The resulting solution is :(A) neutral (B) acidic (C) strongly acidic (D) alkaline 16. If equal volumes of 0.1 M KMnO4 and 0.1 M K2Cr2O7 solutions are allowed to oxidise Fe2+ to Fe3+ in acidic medium, then Fe2+ oxidised will be :(A) more by KMnO4 (B) more by K2CrO7 (C) equal in both cases (D) can't be determined 17. If 10 g of V2O5 is dissolved in acid and is reduced to V2+ by zinc metal, how many mole I2 could be reduced by the resulting solution if it is further oxidised to VO2+ ions ? [Assume no change in state of Zn2+ ions] (V = 51, O = 16, I = 127) : (A) 0.11 mole of I2 (B) 0.22 mole of I2 (C) 0.055 mole of I2 (D) 0.44 mole of I2 18. Given that 50.0 mL of 0.01 M Na2S2O3 solution and 5 × 10–4 mole of Cl2 react according to equation, Cl2 (g) + S2O32– SO42– + Cl– + S Answer the following : The balanced molecular equation is : (A) Cl2 + H2O + Na2S2O3  Na2SO4 + S + 2HCl (B) Cl2 + Na2S2O3  2NaCl + Na2SO4 2– 2– – (C) Cl2 + S2O3  SO4 + S + Cl (D) none of these (i) (ii) How many moles of S2O32– are in the above sample :(A) 0.00050 (B) 0.0025 (C) 0.01 (D) 0.02 (iii) How many equivalents of oxidising agents are in this sample for the above reaction :(A) 0.001 (B) 0.080 (C) 0.020 (D) 0.010 (iv) What is the molarity of Na2SO4 in this solution :(A) 0.080 M (B) 0.040 M 19. (C) 0.020 M (D) 0.010 M One gram of Na3AsO4 is boiled with excess of solid Kl in presence of strong HCl. The iodine evolved is absorbed in Kl solution and titrated against 0.2 N hyposolution. Assuming the reaction to be AsO43– + 2H+ + 2I–  AsO33– + H2O + I2, calculate the volume of thiosulphate hypo consumed. [Atomic weight of As = 75] (A) 48.1 mL (B) 38.4 mL (C) 24.7 mL (D) 30.3 mL REDOX REACTION AND EQUIVALENT CONCEPT 20. Which of the following samples of reducing agents is/are chemically equivalent to 25 mL of 0.2 N KMnO4 to be reduced to Mn2+ and water :(A) 50 mL of 0.2 M FeSO4 to be oxidized to Fe3+ (B) 50 mL of 0.1 M H3AsO3 to be oxidized to H3AsO4 (C) 50 mL of 0.1 M H2O2 to be oxidized to H+ and O2 (D) 25 mL of 0.1 M SnCl2 to be oxidized to Sn4+ 21. Find the volume of strength of H2O2 solution prepared by mixing of 250 mL of 3N H2O2 & 750 mL of 1N H2O2 solution (A) 1.5 V (B) 8.4 V (C) 5.6 V (D) 11.2 V 22. 0.3 g of an oxalate salt was dissolved in 100 mL solution. The solution required 90 mL of N/20 KMnO 4 for complete oxidation. The % of oxalate ion in salt is :(A) 33% (B) 66% (C) 70% (D) 40% 23. A 0.518 g sample of limestone is dissolved in HCl and then the calcium is precipitated as CaC2O4. After filtering and washing the precipitate, it requires 40.0 mL of 0.250 N KMnO4 solution acidified with H2SO4 to titrate it as. The percentage of CaO in the sample is :MnO4– + H+ + C2O42–  Mn2+ + CO2 + 2H2O (A) 54.0 % (B) 27.1 % (C) 42 % (D) 84 % 24. In the reaction CrO5 + H2SO4  Cr2(SO4)3 + H2O + O2 one mole of CrO5 will liberate how many moles of O2 :(A) 5/2 (B) 5/4 (C) 9/2 (D) 7/2 25. 25 mL of 0.50 M H2O2 solution is added to 50 mL of 0.20 M KMnO4 in acid solution. Which of the following statement are true :(A) 0.010 mole of oxygen is liberated (B) 0.005 mole of KMnO4 are left (C) 0.030 g atom of oxygen gas is evolved (D) 0.0025 mole H2O2 does not react with KMnO4 26. Hydrogen peroxide in aqueous solution decomposes on warming to give oxygen according to the equation 2H2O2 (aq) 2H2O () + O2 (g) Under conditions where 1 mole of gas occupies 24 dm3. 100 cm3 of XM solution of H2O2 produces 3 dm3 of O2. Thus X is :(A) 2.5 (B) 1 (C) 0.5 (D) 0.25 27. Bottle (A) contain 320 mL of H2O2 solution & labeled with 10 V H2O2 & Bottle (B) contain 80 mL H2O2 having normality 5N. If bottle (A) & bottle (B) mixed & solution filled in bottle (C). Select the correct lable for bottle (C) in term of volume strength & in term of g / litre. :(A) 13.6 "V" & 41.285 g/L (B) 11.2 "V" & 0.68 g/L (C) 5.6 "V" & 0.68 g/L (D) 5.6 "V" & 41.285 g/L 28. Temporary hardness is due to HCO3– of Mg2+ and Ca2+. It is removed by addition of CaO. Ca(HCO3)2 + CaO  2CaCO3 + H2O Mass of CaO required to precipitate 2 g CaCO3 is :(A) 2.00 (B) 0.56 g (C) 0.28 g (D) 1.12 g 29. An ore of iron, Wustite has the formula F0.93O1.00. The mole fraction of total iron present in the form of Fe(II) is :(A) 0.82 (B) 0.85 (C) 0.15 (D) 0.37 30. HNO3 oxidises NH4+ ions to nitrogen and itself gets reduced to NO2. The moles of HNO3 required by 1 mol of (NH4)2SO4 is :(A) 4 (B) 5 (C) 6 (D) 2 31. 25 mL of a 0.1 M solution of a stable cation of transition metal Z reacts exactly with 25 ml of 0.04 mL acidified KMnO4 solution. Which of the following is most likely to represent the change in oxidation state of Z correctly :(A) Z+  Z2+ (B) Z2+  Z3+ (C) Z3+  Z4+ (D) Z2+  Z4+ 32. 1 mol of iron (Fe) reacts completely with 0.65 mol O2 to give a mixture of only FeO and Fe2O3. Mole ratio of ferrous oxide to ferric oxide is :(A) 3 : 2 (B) 4 : 3 (C) 20 : 13 (D) none of these 33. The molar ratio of Fe++ to Fe+++ in a mixture of FeSO4 and Fe2(SO4)3 having equal number of sulphate ion in both ferrous and ferric sulphate is :(A) 1 : 2 (B) 3 : 2 (C) 2 : 3 (D) can't be determined 34. If a piece of iron gains 10% of its weight due to partial rusting into Fe2O3. The percentage of total iron that has rusted is :(A) 23 (B) 13 (C) 23.3 (D) 25.67 35. How many litres of Cl2 at S.T.P. will be liberated by oxidation of NaCl with 10 g KMnO4 :(A) 3.54 litres (B) 7.08 litres (C) 1.77 litres (D) none of these 36. During the disproportionation of iodine to iodide and iodate ions, the ratio of iodate and iodide ions formed in alkaline medium is :(A) 1 : 5 (B) 5 : 1 (C) 3 : 1 (D) 1 : 3 37. 28 NO3– + 3As2S3 + 4H2O  6AsO43– + 28 NO + 9SO42– + H+ What will be the equivalent mass of As2S3 in above reaction M.wt. M.wt. M.wt. (A) (B) (C) 2 4 24 38. (D) M.wt. 28 CN– is oxidised by NO3– in presence of acid : a CN– + b NO3– + c H+  (a + b) NO + a CO2 + What are the values of a, b, c in that order : (A) 3,7,7 (B) 3,10,7 (C) 3,10,10 c HO 2 2 (D) 3,7,10 39. Which of the following solutions will exactly oxidize 25 mL of an acid solution of 0.1 M Fe (II) oxalate :(A) 25 mL of 0.1 M KMnO4 (B) 25 mL of 0.2 M KMnO4 (C) 25 mL of 0.6 M KMnO4 (D) 15 mL of 0.1 M KMnO4 40. 4.9 gm of K2Cr2O7 is taken to prepare 0.1 L of the solution. 10 mL of this solution is further taken to oxidise Sn2+ ion into Sn4+ ion Sn4+ so produced is used in 2nd reaction to prepare Fe3+ ion then the millimoles of Fe3+ ion formed will be (assume all other components are in sufficient amount) [Molar mass of K2Cr2O7 = 294 g]. (A) 5 (B) 20 (C) 10 (D) none of these 41. When ZnS is boiled with strong nitric acid, the products are zinc nitrate, sulphuric acid and nitrogen dioxide. What are the changes in the oxidation numbers of Zn, S and N. (A) +2, +4, –1 (B) +2, +6, –2 (C) 0, +4, –2 (D) 0, +8, –1 42. When arsenic sulphide is boiled with NaOH, sodium arsenite and sodium thioarsenite are formed y x As2S3 + y NaOH  Na3AsO3 + x Na3AsS3 + H O. What are the values of x and y ? 2 2 (A) 1, 6 (B) 2, 8 (C) 2, 6 (D) 1, 4 43. An element forms two different sulphates in which its weight % is 28 and 37. What is the ratio of oxidation numbers of the element in these sulphates ? (A) 1 : 2 (B) 1 : 3 (C) 2 : 1 (D) 3 : 2 44. The following equations are balanced atomwise and chargewise. (i) Cr2O72– + 8H+ + 3H2O2  2Cr3+ + 7H2O + 3O2 (ii) Cr2O72– + 8H+ + 5H2O2  2Cr3+ + 9H2O + 4O2 (iii) Cr2O72– + 8H+ + 7H2O2  2Cr3+ + 11H2O + 5O2 The precise equation/equations representing the oxidation of H2O2 is /are : (A) (i) only (B) (ii) only (C) (iii) only (D) all the three REDOX REACTION AND EQUIVALENT CONCEPT 45. 35 mL sample of hydrogen peroxide gives of 500 mL of O2 at 27°C and 1 atm pressure. Volume strength of H2O2 sample will be :(A) 10 volume (B) 13 volumes (C) 11 volume (D) 12 volume 46. 20 mL of 0.1 M solution of compound Na2CO3.NaHCO3.2H2O is titrated against 0.05 M HCl, x mL of HCl is used when phenolphthalein is used as an indicator and y mL of HCl is used when methyl orange is the indicator in two separate titrations. Hence (y – x) is :(A) 40 mL (B) 80 mL (C) 120 mL (D) none of these 47. A mixture of H2SO4 and H2C2O4 (oxalic acid) and some inert impurity weighing 3.185 g was dissolved in water and the solution made up to 1 litre, 10 mL of this solution required 3 mL of 0.1 N NaOH for complete neutralization. In another experiment 100 mL of the same solution in hot condition required 4 mL of 0.02M KMnO4 solution for complete reaction. The wt. % of H2SO4 in the mixture was :(A) 40 48. (B) 50 (C) 60 (D) 80 0.80 g of sample of impure potassium dichromate was dissolved in water and made upto 500 mL solution. 25 mL of this solution treated with excess of KI in acidic medium and I2 liberated required 24 mL of a sodium thiosulphate solution. 30 mL of this sodium thiosulphate solution required 15 mL of N/20 solution of pure potassium dichromate. What was the percentage of K2Cr2O7 in given sample? (A) 73.5 % 49. (B) 75.3 % (C) 36.75 % (D) none of these 0.10 g of a sample containing CuCO3 and some inert impurity was dissolved in dilute sulphuric acid and volume made up to 50 mL. This solution was added into 50 mL of 0.04 M KI solution where copper precipitates as CuI and I – is oxidized into I3– . A 10 mL portion of this solution is taken for analysis, filtered and made up free I 3– and then treated with excess of acidic permanganate solution. Liberated iodine required 20 mL of 2.5 mM sodium thiosulphate solution to reach the end point. Determine weight percentage of CuCO3 in the original sample. (A) 7.41 50. (B) 74.1 (C) 61.75 (D) none of these A 150 mL of solution of I2 is divided into two unequal parts. I part reacts with hypo solution in acidic medium. 15 mL of 0.4 M hypo was consumed. II part was added with 100 mL of 0.3 M NaOH solution. Residual base required 10 mL of 0.3 M H2SO4 solution for complete neutralization. What was the initial concentration of I 2 ? (A) 0.08 M (B) 0.1 M (C) 0.2 M (D) none of these EXERCISE - 1 1. D 2. A 3. C 4. C 5. B 6. D 7. D 8. (iii) A C 9. A (iv) D 10. B 11. C 12. A 13. C 19. A 20. D 21. B 22. B 14. C 15. A 16. B 17. A 18. (i) A (ii) A 23. A 24. D 25. B 26. A 27. A 28. B 29. B 30. C 31. D 32. B 33. B 34. C 35. A 36. A 37. D 38. D 39. D 40. C 41. D 42. A 43. D 44. A 45. B 46. B 47. A 48. A 49. B 50. B