Redox Reaction and Equivalent Concept Exercise # 4

REDOX REACTION AND EQUIVALENT CONCEPT Exercise # 4 1. [Subjective Type Questions] n+ – 2+ –3 n+ KMnO4 oxidizes X ion to XO3 , itself changing to Mn in acid medium. 2.68 × 10 mole of X requires –3 – 1.61 × 10 mole of MnO4 . What is the value of n? Also calculate the atomic mass of X, if the weight of 1g equivalent of XCln is 56. 2. In a quantitative determination of iron in an ore, an analyst converted 0.40 g, of the ore into its ferrous. This required 40.00 mL of 0.1 N solution of KMnO4 for titration. (i) How many milliequivalents of KMnO4 does 40.00 mL of 0.1 N solution represent? (ii) How many equivalents of iron were present in the sample of the ore taken for analysis? (iii) How many grams of iron were present in the sample? (iv) What is the percentage of iron in the ore? (v) What is the molarity of KMnO4 solution used? (vi) How many moles of KMnO4 were used for titration ? (Fe = 56) 3. The mixture of CuS (molar weight = M1) and Cu2S (molecular weight = M2) oxidised by KMnO4 (molecular weight = M3) 2+ in acidic medium, the product obtained are Cu , SO2. Find the equivalent weight of CuS, Cu2S and KMnO4 respectively. 4. Calculate the oxidation number of underlined elements in the following compounds : (a) K[ Co(C2O4)2.(NH3)2] (b) K4 P2O7 (c) Cr O2Cl2 (d) Na2[ Fe(CN)5NO ] (e) Mn3O4 (f) Ca(ClO2)2 (g) [ Fe(NO)(H2O)5]SO4 (h) ZnO2 + 5. 2– (c) Fe0.93O Write balanced net ionic equation for the following reactions in acidic solution. 2– 3+ (a) S4O6 (aq) +Al (s)  H2S (aq) + Al (aq) 2– 2– 2– 3+ (b) S2O3 (aq) + Cr2O7 (aq)  S4O6 (aq) + Cr (aq) – – – – (c) ClO3 (aq) + As2S3 (s)  Cl (aq) + H2AsO4 (aq) + HSO4 (aq) – – – (d) IO3 (aq) + Re (s)  ReO4 (aq) + I (aq) – – (e) HSO4 (aq) + As4 (s) + Pb3O4 (s)  PbSO4 (s) + H2AsO4 (aq) (f) 6. – HNO2 (aq)  NO3 + NO (g) Write balanced net ionic equations for the following reactions in basic solution : 2– – 2– – (a) C4H4O6 (aq) + ClO3 (aq)  CO3 (aq) + Cl (aq) – (b) Al (s) + BiONO3 (s)  Bi (s) + NH3 (aq) + Al (OH)4 (aq) – (c) H2O2 (aq) + Cl2O7 (aq)  ClO2 (aq) + O2 (g) (d) Tl2O3 (s) + NH2OH (aq)  TlOH (s) + N2 (g) 2+ 2– 2– (e) Cu(NH3)4 (aq) + S2O4 (aq)  SO3 (aq) + Cu (s) + NH3 (aq) (f) – Mn(OH)2 (s) + MnO4 (aq)  MnO2 (s) + – – – – 7. Consider the reaction H + IO 4 + I  I2 + H2O. Find the ratio of coefficients of IO4 , I and I2. 8. A dilute solution of H2SO4 is made by adding 5 mL of 3N H2SO4 to 245 mL of water. Find the normality and molarity of the solution. 9. What volume at NTP of gaseous ammonia will be required to be passed into 30 cc of N – H2SO4 solution to bring down the acid strength of the latter to 0.2 N. 10. 10 g CaCO3 were dissolved in 250 mL of M HCl and the solution was boiled. What volume of 2 M KOH would be required to equivalence point after boiling? Assume no change in volume during boiling. 11. H3PO4 is a tri basic acid and one of its salt is NaH2PO4. What volume of 1 M NaOH solution should be added to 12 g of NaH2PO4 to convert it into Na3PO4? 12. 1.64 g of mixture of CaCO3 and MgCO3 was dissolved in 50 mL of 0.8 M HCl. The excess of acid required 16 mL of 0.25 M NaOH for neutralization. Calculate the percentage of CaCO3 and MgCO3 in the sample. 13. A solution containing 4.2 g of KOH and Ca(OH2) is neutralized by an acid. It consums 0.1 equivalent of acid, calculate the percentage composition of the sample. 14. How many mL of 0.1 N HCl are required to react completely with 1 g mixture of Na2CO3 and NaHCO3 containing equimolar amounts of two? 15. 0.5 g of fuming H2SO4 (oleum) is diluted with water. The solution requires 26.7 mL of 0.4N NaOH for complete neutralization. Find the % of free SO3 in the sample of oleum. 16. 1.5 g of chalk were treated with 10 mL of 4N – HCl. The chalk was dissolved and the solution made to 100 mL, 25 mL of this solution required 18.75 mL of 0.2 N – NaOH solution for complete neutralisation. Calculate the percentage of pure CaCO3 in the sample of chalk? 17. A solution contains Na2CO3 and NaHCO3. 20 mL of this solution required 4 mL of 1N – HCl for titration with Ph indicator. The titration was repeated with the same volume of the solution but with MeOH. 10.5 mL of 1 – N HCl was required this time. Calculate the amount of Na2CO3 & NaHCO3. 18. A solution contains a mix of Na2CO3 and NaOH. Using Ph as indicator 25 mL of mixture required 19.5 mL of 0.995 N HCl for the end point. With MeOH, 25 mL of the solution required 25 mL of the same HCl for the end point. Calculate g/L of each substance in the mixture. 19. 4+ 2+ 4+ It required 40.05 mL of 1 M Ce to titrate 20 mL of 1 M Sn to Sn . What is the oxidation state of the cerium in the product. 20. 2+ A volume of 12.53 mL of 0.05093 M SeO2 reacted with exactly 25.52 mL of 0.1 M CrSO4. In the reaction, Cr was 3+ oxidized to Cr . To what oxidation state was selenium converted by the reaction. 21. Pottasium acid oxalate K2C2O4.3H2C2O4.4H2O can be oxidized by MnO4 in acid medium. Calculate the volume of 0.1 M KMnO4 reacting in acid solution with one gram of the acid oxalate. 22. N HCl. 17.5 mL of HCl was 10 required for end point. After this MeOH was added and 2.5 mL of same HCl was again required for next end point. 200 mL of a solution of mixture of NaOH and Na2CO3 was first titrated with Ph and Find out amounts of NaOH and Na2CO3 in the mix. REDOX REACTION AND EQUIVALENT CONCEPT 23. A solution contains Na2CO3 and NaHCO3. 10 mL of this requires 2 mL of 0.1 M H2SO4 for neutralisation using Ph indicator. MeOH is then added when a further 2.5 mL of 0.2 M H2SO4 was needed. Calculate strength of Na2CO3 and NaHCO3. 24. A sample containing Na2CO3 & NaOH is dissolved in 100 mL solution. 10 mL of this solution requires 25 mL of 0.1 N HCl when Ph is used as indicator. If MeOH is used as indicator 10 mL of same solution requires 30 mL of same HCl. Calculate % of Na2CO3 and NaOH in the sample. 25. 3 A 1.0 g sample of H2O2 solution containing x% H2O2 by mass requires x cm of a KMnO4 solution for complete oxidation under acidic conditions. Calculate the normality of KMnO4 solution. 26. Metallic tin in the presence of HCl is oxidized by K2Cr2O7 to stannic chloride, SnCl4. What volume of decinormal dichromate solution would be reduce by 1 g of tin. 27. 5 g sample of brass was dissolved in one litre dil. H2SO4. 20 mL of this solution were mixed with KI, liberating + I2 and Cu and the I2 required 20 mL of 0.0327 N hypo solution for complete titration. Calculate the percentage of Cu in the alloy. 28. One g of impure sodium carbonate is dissolved in water and the solution is made up to 250 mL. To 50 mL of this made up solution, 50 mL of 0.1 N – HCl is added and the mix after shaking well required 10 mL of 0.16 N – NaOH solution for complete titration. Calculate the % purity of the sample. 29. What amount of substance containing 60% NaCl, 37% KCl should be weighed out for analysis so that after the + action of 25 mL of 0.1 N AgNO3 solution, excess of Ag is back titrates with 5 mL of NH4SCN solution. Given that 1 mL of NH4SCN = 1.1. mL of AgNO3. 30. A bottle labelled with "12 V H2O2" contain 700 mL solution. If a student mix 300 mL water in it what is the g/litre strength & normality and volume strength of final solution. 31. 0.84 g iron ore containing x percent of iron was taken in a solution containing all the iron in ferrous condition. The solution required x mL of a dichromatic solution for oxidizing the iron content to ferric state. Calculate the strength of dichromatic solution. 32. The neutralization of a solution of 1.2 g of a substance containing a mixture of H2C2O4.2H2O, KHC2O4.H2O and different impurities of a neutral salt consumed 18.9 mL of 0.5 N NaOH solution. On titration with KMnO4 solution, 0.4 g, of the same substance needed 21.55 mL of 0.25 N KMnO4. Calculate the % composition of the substance. 33. 50 g of a sample of Ca(OH)2 is dissolved in 50 mL of 0.5 N HCl solution. The excess of HCl was titrated with 0.3 N – NaOH. The volume of NaOH used was 20cc. Calculate % purity of Ca(OH) 2. 34. 50 mL of an aqueous solution of H2O2 were treated with an excess of KI solution and dilute H2SO4, the liberated iodine required 20 mL of 0.1 N Na2S2O3 solution for complete interaction. Calculate the concentration of H2O2 in g/. 35. 100 kg hard water contains 5 g MgSO4. Find hardness. 36. One litre hard water contains 1 mg CaCl2 and 1 mg MgSO4. Find hardness. 37. Calculate the amount of lime Ca(OH)2 required to remove the hardness in 60 litre of pond water containing 1.62 mg of calcium bicarbonate per 100 mL of water. 38. 10 g sample of bleaching powder was dissolved into water to make the solution one litre. To this solution 35 mL of 1.0 M Mohr salt solution was added containing enough H2SO4. After the reaction was complete, the excess Mohr salt required 30 mL of 0.1 M KMnO 4 for oxidation. Find out the % of available Cl 2 approximately is (mol wt. 71). 39. –2 Calculate the amount (in milligrams) of SeO3 in solution on the basis of following data 20 mL of M/60 solution –2 of KBrO3 was added to a definite volume of SeO3 solution. The bromine evolved was removed by boiling and excess of KBrO3 was back titrated with 5 mL of M/25 solution of NaAsO2. The reactions are given below. (Atomic mass of K = 39, Br = 80, As = 75, Na = 23, O = 16, Se = 79) –2 – + –2 (a) SeO3 + BrO3 + H SeO4 + Br2 + H2O – – – –3 (b) BrO3 + AsO2 + H2O Br + AsO4 + H + 40. Calculate the hardness of water sample which contains 0.001 mol MgSO4 per litre of water. 41. A solution of a 0.4 g sample of H2O2 reacted with 0.632 g of KMnO4 in the presence of sulphuric acid. Calculate the percentage purity of the sample of H2O2. 42. 5 litre of a solution of H2O2 with x N strength is diluted to 5.5 litre. This 5.5 litre H2O2 solution gives 28 litre O2 at NTP. Find the value of x. 43. A 1.0 g sample of Fe2O3 solid of 55.2% purity is dissolved in acid and reduced by heating the solution with zinc dust. The resultant solution is cooled and made upto 100.0 mL. An aliquot of 25.0 mL of this solution requires 17.0 mL of 0.0167 M solution of an oxidant for titration. Calculate the number of moles of electrons taken up by the oxidant in the reaction of the above titration. 44. 25 mL of a solution containing HCl was treated with excess of M/5 KIO3 and KI solution of unknown concentration where I2 liberated is titrated against a standard solution of 0.021 M Na2S2O3 solution whose 24 mL were used up. Find the strength of HCl and volume of KIO3 solution consumed : 45. 0.6213 g of sample contains an unknown amount of As2O3. The sample was treated with HCl resulting information of AsCl3 (g) which was distilled into a beaker of water. The hydrolysis reaction is as follows : AsCl3 + 2H2O  HAsO2 + 3H+ + 3Cl– The amount of HAsO2 was determined by titration with 0.04134 M I2, requiring 23.04 mL to reach the equivalence point. The redox products in the titration were H3AsO4 and I–. Find the amount of KMnO4 needed to oxidize As in As2O3 to its maximum possible oxidation state in acidic medium. 46. A sample of steel weighing 0.6 g and containing S as an impurity was burnt in a stream of O2, when S was converted to its oxide SO 2 .SO 2 was then oxidized to SO 4– – by using H 2 O 2 solution containing 30 mL of 0.04 M NaOH. 22.48 mL of 0.024 M HCl was required to neutralize the base remaining after oxidation. Calculate the % of S in the sample : 47. 1.2475 g of crystalline copper sulphate was dissolved in water and excess of KI was added. The liberated iodine consumed 50 mL N/10 Na2S2O3 solution to reach the end point of the titration. Calculate the number of water molecules of hydration in crystalline copper sulphate salt. 48. A 1g sample of K2Cr2O7 containing some inert material was entirely reduced with conc. HCl. The chlorine liberated was passed through hot solution of NaOH at 800C, and it completely diproportionates to form ClO3 and Cl. This NaClO3 was isolated and its reduction with KI (aq) liberated iodine, giving Cl.The iodine thus liberated required 100 mL of decinormal hypo solution for complete titration. What is the percentage purity of the dichromate sample? REDOX REACTION AND EQUIVALENT CONCEPT 49. 2.5g of mixture of crystalline oxalic acid (H2C2O4. 2H2O) and sodium oxalate (Na2C2O4) was dissolved in 100 mL of water. 50 mL of this solution was titrated against N/10 NaOH solution when 119.05 mL of the base was found necessary to reach the end point with phenolphthalein as the indicator. 1g of the mixture was dissolved in water and the solution titrated against N/10 KMnO4 in the presence of dil. H2SO4. What is the volume of KMnO4 needed for getting the end point with 0.5g of the mixture? 50. In the presence of fluoride ion, Mn2+ can be titrated with MnO4–, both reactants being converted to a complex of Mn(III). A 0.545 g sample containing Mn3O4 was dissolved and all manganese was converted to Mn2+. Titration in the presence of fluoride ion consumed 31.1 mL of KMnO4 that was 0.177 N against oxalate. (a) write a balanced chemical equation for the reaction, assuming that the complex is MnF4–. (b) what was the % of Mn3O4 in the sample ? 51. A mixture of two gases, H2S and SO2 is passed through three beakers successively. The first beaker contains Pb2+ ions, which absorbs S2– forming PbS. The second beaker contains 25 mL of 0.0396 N I2 to oxidize SO2 to SO42–. The third contains 10 mL of 0.0345 N thiosulphate solution to retain any I2 carried over from the second absorber. A 25 L gas sample was passed through the apparatus followed by an additional amount of N 2 to sweep last traces of SO2 from first and second absorber. The solution from the first absorber was made acidic and treated with 20 mL of 0.0066 M K2Cr2O7 which converted S2– to SO2. The excess dichromate was reacted with solid KI and the liberated iodine required 7.45 mL of 0.0345 N Na2S2O3 solution. The solutions in the second and third absorbers were combined and the resultant iodine was titrated with 2.44 mL of the same thiosulphate solution. Calculate the concentrations of SO2 and H2S in mg/L of the sample : 52. 1 g of a moist sample of a mixture of KClO 3 and KCl was dissolved in water and made upto 250 mL. 25 mL of this solution was treated with SO2 to reduced chlorate into chloride and the excess SO2 was boiled off. When the total chloride was precipitated, 0.1435 g of AgCl was obtained. In another experiment 25 mL of the original solution was treated with 30 mL of 0.2 N solution of FeSO4 and unreacted FeSO4 required 37.5 mL of 0.08 N solution of an oxidizing agent for complete oxidation. Calculate the molar ratio of chlorate and chloride in the given mixture. Fe2+ reacts with ClO3– according to equation : ClO3– + 6Fe2+ + 6H+  Cl– + 6Fe3+ + 3H2O Also calculate the mass percent of moisture present in the moist sample. 53. A 1 g sample containing NaOH as the only basic substance and some inert impurity was left exposed to atmosphere for a very long time so that part of NaOH got converted into Na2CO3 by absorbing CO2 from atmosphere. The resulting sample was dissolved in water and volume made upto 100 mL. A 20 mL portion of this solution required 16 mL 0.25 M HCl solution to reach the equivalence point when methyl orange was used as indicator. In a separate analysis, 20 mL portion of the same solution was taken along with phenolphthalein indicator and mixed with 50 mL of 0.1 M HCl solution. An additional 9.00 mL 0.1 M Ba(OH)2 solution was required to just restore the pink colour of solution. Determine mass percentage of NaOH in the original sample and mass percentage of Na 2CO3 in the sample after exposure to atmosphere. 54. A steel sample is to be analysed for Cr and Mn simultaneously. By suitable treatment the Cr is oxidized to Cr 2O72– and the Mn to MnO4–. A 10.00 g sample of steel is used to produce 250.0 mL of a solution containing Cr2O72– and MnO4–. A 10.00 mL portion of this solution is added to a BaCl2 solution and by proper adjustment of the acidity, the chromium is completely precipitated as BaCrO4 ; 0.0549 g is obtained. A second 10.00 mL portion of this solution requires exactly 15.95 mL of 0.0750 M standard Fe2+ solution for its titration (in acid solution). Calculate the % of Mn and % of Cr in the steel sample. 55. 1.16 g CH3(CH2)nCOOH was burnt in excess air and the resultant gases (CO2 and H2O) were passed through excess NaOH solution. The resulting solution was divided in two equal parts. One part required 50 mL of 1 N HCl for neutralization using phenolphthalein as indicator. Another part required 80 mL of 1 N HCl for neutralization using methyl orange as indicator. Find the value of n and the amount of excess NaOH solution taken initially. 56. A 1.5 g sample containing oxalic acid and some inert impurity was dissolved in enough water and volume made up to 250 mL. A 20 mL portion of this solution was then mixed with 30 mL of an alkali solution. The resulting solution was then treated with stoichiometric amount of CaCl2 just needed for precipitation of oxalate as CaC2O4. Solution was filtered off and filtrate was finally titrated against 0.1 M HCl solution. 8.0 mL of acid was required to reach the equivalence point. At last, the above neutral solution was treated with excess of AgNO3 solution and AgCl obtained was washed, dried and weighed to be 0.4305 g. Determine mass percentage of oxalic acid in the original sample :