Redox Reaction and Equivalent Concept Exercise # 2

Exercise # 2 1. Part # I [Multiple Correct Choice Type Questions] In the titration of K2Cr2O7 and ferrous sulphate , following data is obtained : V1 mL of K2Cr2O7 solution of molarity M1 requires V2 mL of FeSO4 solution of molarity M2. Which of the following relations is/are true for the above titration : (A) 6 M1V1 = M2V2 2. (B) M1V1 = 6 M2V2 (C) N1V1 = N2V2 (D) M1V1 = M2V2 Choose the correct statement(s) : (A) 1 mole of MnO4– ion can oxidise 5 moles of Fe2+ ion in acidic medium. (B) 1 mole of Cr2 O72– ion can oxidise 6 moles of Fe2+ ion in acidic medium. (C) 1 mole of Cu2S can be oxidised by 1.6 moles of MnO4– ion in acidic medium. (D) 1 mole of Cu2S can be oxidised by 1.33 moles of Cr2O72– ion in acidic medium. 3. Which of the following samples of reducing agents is /are chemically equivalent to 25 mL of 0.2 N KMnO 4 to be reduced to Mn2+ and water : (A) 25 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) 25 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+ 4. 0.1 M solution of KI reacts with excess of H2SO4 and KO3 solutions, according to equation 5– + O3– + 6H+  32 + 3H2O ; which of the following statements is/are correct : (A) 200 mL of the K solution react with 0.004 mole KIO3. (B) 100 mL of the K solution reacts with 0.006 mole of H2SO4. (C) 0.5 litre of the K solution produced 0.005 mole of I2.  Molecular Weight  (D) Equivalent weight of KO3 is equal to  . 5   5. 6. Consider the redox reaction 2S2O32– + 2  S4O62– + 2 – : (A) S2O32– gets reduced to S4O62– (B) S2O32– gets oxidised to S4O62– (C) 2 gets reduced to – (D) 2 gets oxidised to – There are two sample of HCl having molarity 1N and 0.25 N. Find volume of these sample taken in order to prepare 0.75 N HCl solution. (Assume no water is used) : (A) 20 mL, 10 mL 7. (B) 100 mL, 50 mL (C) 40 mL, 20 mL (D) 50 mL, 25 mL To a 25 ml H2O2 solution excess acidified solution of KI was added. The iodine liberated 20 ml of 0.3 N sodium thiosulphate solution. Use these data to choose the correct statements from the following : (A) The weight of H2O2 present in 25 ml solution is 0.102 g (B) The molarity of H2O2 solution is 0.12 M (C) The weight of H2O2 present in 1 L of the solution is 0.816 g (D) The volume strength of H2O2 is 1.344 L REDOX REACTION AND EQUIVALENT CONCEPT 8. A + B  A3B2 (unbalanced) A3B2 + C  A3B2C2 (unbalanced) Above two reactions are carried out by taking 3 moles each of A and B and one mole of C. Then which option is/are correct ? 9. 10. (A) 1 mole of A3B2C2 is formed (B) 1 2 mole of A3B2C2 is formed (C) 1/2 mole of A3B2 is formed (D) 1/2 mole of A3B2 is left finally Consider the redox reaction 2S2O32– + 2  S4O62– + 2 – : (A) S2O32– gets reduced to S4O62– (B) S2O32– gets oxidised to S4O62– (C) 2 gets reduced to – (D) 2 gets oxidised to – If 100 ml of 1M H2SO4 solution is mixed with 100 ml of 9.8%(w/w) H2SO4 solution (d = 1 g/ml) then : (A) concentration of solution remains same (B) volume of solution become 200 ml (C) mass of H2SO4 in the solution is 98 gm (D) mass of H2SO4 in the solution is 19.6 gm 11. Equal volume of 0.1M NaCl and 0.1M FeCl2 are mixed with no change in volume due to mixing. Which of the following will be true for the final solution. (No precipitation occurs). Assume complete dissociation of salts and neglect any hydrolysis. (A) [Na+] = 0.05 M 12. (B) [Fe2+] = 0.05M (C) [Cl] = 0.3M (D) [Cl] = 0.15M Silver metal in ore is dissolved by potassium cyanide solution in the presence of air by the reaction 4 Ag + 8 KCN + O2 + 2H2O  4 K[Ag (CN)2] + 4 KOH (A) The amount of KCN required to dissolve 100 g of pure Ag is 120 g. (B) The amount of oxygen used in this process is 0.742 g (for 100 gm pure Ag) (C) The amount of oxygen used in this process is 7.40 g (for 100 gm pure Ag) (D) The volume of oxygen used at STP is 5.20 litres. 13. If 27 g of Carbon is mixed with 88 g of Oxygen and is allowed to burn to produce CO2 , then : (A) Oxygen is the limiting reagent. (B) Volume of CO2 gas produced at NTP is 50.4 L. (C) C and O combine in mass ratio 3 : 8. (D) Volume of unreacted O2 at STP is 11.2 L. 14. Equal masses of SO2 and O2 are placed in a flask at STP choose the correct statement. (A) The number of molecules of O2 are more than SO2 (B) Volume occupied at STP is more for O2 than SO2 (C) The ratio of number of atoms of SO2 and O2 is 3 : 4. (D) Moles of SO2 is greater than the moles of O2 . 15. For the reaction 2P + Q  R, 12 mol of P and 8 mol of Q are taken then (A) 3 mol of R is produced (B) 6 mol of R is produced (C) 25% of Q is left behind (D) 25% of Q has reacted . The molality of a sulphuric acid solution is 0.2. Calculate the total weight of the solution having 1000 gm of solvent. (A) 1000 g 17. 18. (B) 1098.6 g (C) 980.4 g (D) 1019.6g If H2SO4 is formed from it’s elements by taking 6.023 × 1023 atom of ‘O’ 5.6 litre of H2 gas at STP and 8 gm S then (A) 0.125 moles of H2SO4 are formed (B) 0.25 moles of H2SO4 are formed (C) no moles of ‘S’ are left (D) 1/4 mole of O2 is left A 5L vessel contains 2.8 g of N2 . When heated to 1800 K , 30% molecules are dissociated into atoms. (A) Total no. of moles in the container will be 0.13 (B) Total no. of molecules in the container will be close to 0.421 × 10 23. (C) Total no. of moles in the container will be 0.098. (D) All of these are correct. 19. The density of air is 0.001293 g/cm3 at STP. Identify which of the following statement is correct (A) Vapour density is 14.48 (B) Molecular weight is 28.96 (C) Vapour density is 0.001293 g/cm3 (D) Vapour density and molecular weight cannot be determined. 20. Which of the following has same mass (A) 1.0 mole of O2 (B) 3.01 × 1023 molecules of SO2 (C) 0.5 moles of CO2 (D) 1 g atom of sulphur Part # II [Assertion & Reason Type Questions] These questions contains, Statement I (assertion) and Statement II (reason). (A) Statement-I is true, Statement-II is true ; Statement-II is correct explanation for Statement-I. (B) Statement-I is true, Statement-II is true ; Statement-II is NOT a correct explanation for statement-I (C) Statement-I is true, Statement-II is false (D) Statement-I is false, Statement-II is true 1. Statement-I : Oxidation involves loss of electrons and reduction involves gain of electrons. Statement-II : The overall reaction in which oxidation and reduction occur simultaneously is called redox reaction. 2. Statement-I : The oxidation state of superoxide ion in KO2, CsO2 and RbO2 is –1/2. Statement-II : Since the oxidation state of an alkali metal in any compound is always +1, the oxidation state of oxygen is –1/2 in the O2– ion. 3. Statement-I : Among Br–, O22–, H– and NO3–, the ions that could not act as oxidising agents are Br– and H–. Statement-II : Br  and H– could not be reduced. 4. Statement-I : H2SO4 cannot act as reducing agent. Statement-II : Sulphur cannot increase its oxidation number beyond +6. REDOX REACTION AND EQUIVALENT CONCEPT 5. Statement-I : In the redox reaction 8 H+ (aq) + 4 NO3– + 6 Cl– + Sn (s) SnCl62– + 4 NO2 + 4 H2O the reducing agent is Sn (s), Statement-II : In balancing half reaction, S2O32– S(s), the number of electrons added on the left is 4. 6. Statement-1 : The molality and molarity of very dilute aqueous solutions differ very little. Statement-2 : The density of water is about 1.0 g cm–3 at room temperature. 7. Statement-1 : For calculating the molality or the mole fraction of solute, if the molarity is known, it is necessary to know the density of the solution. Statement-2 : Molality, molarity and the mole fraction of solute can be calculated from the weight percentage and the density of the solution 8. Statement-1 : Laboratory reagents are usually made up to a specific molarity rather than a given molality. Statement-2: The volume of a liquid is more easily measured than its mass. 9. Statement-1 : Molality and mole fraction concentration units do not change with temperature. Statement-2 : These units are not defined in terms of any volume. 10. Statement-1 : A one molal solution prepared at 20°C will retain the same molality at 100°C, provided there is no loss of solute or solvent on heating. Statement-2 : Molality is independent of temperature. Statement-1 : In the reaction, MnO4– + 5Fe2+ + 8H+  Mn2+ + 5Fe3+ + 4H2O, MnO4– acts as 11. oxidising agent. Statement-2 : : In the above reaction, n-factor for MnO4 is 5. 12. Statement-1 : If 200 mL of 0.1N NaOH is added to 200 mL of 0.1N H2SO4 solution, then the resulting solution is acidic. Statement-2 : If milliequivalents of acid is greater than milliequivalents of base, then upon mixing the solution is acidic. 13. Statement-1 : Equivalent weight of FeC2O4 in the reaction, FeC2O4 + Oxidising agent  Fe3+ + CO2 is M/3, where M is molar mass of FeC2O4. Statement-2 : In the above reaction, total two moles of electrons are given up by 1 mole of FeC2O4 to the oxidising agent. EXERCISE - 2 : PART # I 1. A, C 2. A, B, C, D 3. A, C, D 4. 7. A, B, D 8. B, D 9. B, C 10. A, B, D 11. A, B, D 12. A, C, D 16. D 17. C 18. A, B 13. B, C, D 14. A, B, C 19. A, B 20. A, B, D 15. B, C A, B, D 5. B, C 6. A, B, C, D PART # II 1 B 2 A 3 A 4 A 5 B 6 A 7 B 8 A 9 A 10 A 11 B 12 D 13 C