Mole Concept Exercise # 5

Exercise # 5 1. Part # I [Previous Year Questions] 6.02 × 1020 molecules of urea are present in 100 ml of its solution. The concentration of urea solution is (1) 0.001 M (2) 0.01 M (3) 0.02 M (4) 0.1 M 2. If we consider that 1/6, in place of 1/12, mass of carbon atom is taken to be the relative atomic mass unit, the mass of one mole of a substance will (1) decrease twice (2) increase two fold (3) remain unchanged (4) be a function of the molecular mass of the substance 3. The oxidation state of Cr in [Cr(NH3)4Cl2]+ is : (1) + 3 (2) + 2 (3) + 1 (4) 0 4. The oxidation state of chromium in the final product formed by the reaction between KI and acidified potassium dichromate solution is : (1) + 4 (2) + 6 (3) + 2 (4) + 3 5. Two solution of a substance (non electrolyte) are mixed in the following manner. 480 ml of 1.5M first solution + 250 ml of 1.2M second solution. What is the molarity of the final mixture ? (1) 2.70M (2) 1.344M (3) 1.50M (4) 1.20M 6. Which of the following chemical reactions depicts the oxidizing behaviour of H2SO4? (1) 2HI + H2SO4  I2 + SO2 + 2H2O (2) Ca(OH)2 + H2SO4 CaSO4 + 2H2O (3) NaCl + H2SO4 NaHSO4 + HCl (4) 2PCl5 + H2SO4 2POCl3 + 2HCl + SO2Cl2 How many moles of magnesium phosphate, Mg3(PO4)2 will contain 0.25 mole of oxygen atoms ? (1) 0.02 (2) 3.125 × 10–2 (3) 1.25 × 10–2 (4) 2.5 × 10–2 7. 8. Density of a 2.05M solution of acetic acid in water is 1.02 g/ml. The molality of the solution is : (1) 1.14 mol kg–1 (2) 3.28 mol kg–1 (3) 2.28 mol kg–1 (4) 0.44 mol kg–1 9. In the reaction 2AI(s) + 6HCl(aq)  2Al3+(aq) + 6Cl–(aq) + 3H2 (g) (1) 6L HCl(aq) is consumed for every 3L H2 produced. (2) 33.6 L H2(g) is produced regardless temperature and pressure for every moles that reacts. (3) 67.2 L H2(g) at STP is produced for every mole of Al that reacts . (4) 11.2 L H2(g) at STP is produced for every mole of HCl(aq) consumed. 10. The density (in g mL–1) of a 3.60 M sulphuric acid solution that is 29% (H2SO4 molar mass = 98 g mol–1) by mass will be : (1) 1.22 (2) 1.45 (3) 1.64 (4) 1.88 11. A 5.2 molal aqueous solution of methyl alcohol, CH3OH, is supplied. What is the mole fraction of methyl alcohol in the solution? (1) 0.100 12. (2) 0.190 (3) 0.086 (4) 0.050 The molality of a urea solution in which 0.0100 g of urea, [(NH2)2CO] is added to 0.3000 dm3 of water at STP is: (1) 5.55 × 10–4 (2) 33.3 m (3) 3.33 × 10–2 m (4) 0.555 m MOLE CONCEPT 13. The density of a solution prepared by dissolving 120 g of urea (mol. mass = 60 u) in 1000 g of water is 1.15 g/mL. The molarity of this solution is : (1) 0.50 M (2) 1.78 M (3) 1.02 M (4) 2.05 M 14. For the estimation of nitrogen, 1.4 g of organic compound was digested by Kjeldahl method and the evolved M M sulphuric acid. The unreacted acid required 20 ml of sodium hydrox10 10 ide for complete neutralization. The percentage of nitrogen in the compound is : (1) 3% (2) 5% (3) 6% (4) 10% ammonia was absorbed in 60 mL of 15. The moleclar formula of a commercial resin used for exchanging ions in water softening is C8H7SO3Na (Mol. wt. 206). What would be the maximum uptake of Ca2+ ions by the resin when expressed in mole per gram resin ? (1) 2 309 (2) 1 412 (3) 1 103 (4) 1 206 16. In Carius method of estimation of halogens, 250 mg of an organic compound gave 141 mg of AgBr. The percentage of bromine in the compound is : (at. mass Ag = 108, Br = 80) (1) 48 (2) 60 (3) 24 (4) 36 17. 3 g of activated charcoal was added to 50 mL of acetic acid solution (0.06N) in a flask. After an hour it was filtered and the strength of the filtrate was found to be 0.042N. The amount of acetic acid adsorbed (per gram of charcoal) is : (1) 42 mg (2) 54 mg (3) 18 mg (4) 36 mg At 300 K and 1 atm, 15 mL of a gaseous hydrocarbon requires 375 mL air containing 20% O2 by volume for complete combustion. After combustion the gases occupy 300 mL. Assuming that the water formed is in liquid form and the volumes were measured at the same temperature and pressure, the formula of the hydrocarbon is: (1) C3H8 (2) C4H8 (3) C4H10 (4) C3H6 The most abundant elements by mass in the body of a healthy human adult are : Oxygen (61.4%), Carbon (22.9%), Hydrogen (10.0%), and Nitrogen (2.6%). The weight which a 75 kg person would gain if all 1H atoms are replaced by 2 H atoms is : 18. 19. (1) 15 kg 20. (4) 10 kg (2) 84.3 (3) 118.6 (4) 11.86 The ratio of mass percent of C and H of an organic compound (CXHYOZ) is 6 : 1. If one moleucle of the above compound (CXHYOZ) contains half as much oxygen as required to burn one molecule of compound CXHY completely to CO2 and H2O. The empirical formula of compound CXHYOZ is : (1) C2H4O Part # II 1. (3) 7.5 kg 1 gram of a carbonate (M2CO3) on treatment with excess HCl produces 0.01186 mole of CO2. The molar mass of M2CO3 in g mol–1 is. (1) 1186 21. (2) 37.5 kg (2) C3H4O2 (3) C2H4O3 (4) C3H6O3 [Previous Year Questions] Amongst the following, the pair having both the metals in their highest oxidation state is : (A) [Fe(CN)6]3– and [Co(CN)6]3– (B) CrO2Cl2 and MnO4– (C) TiO2 and MnO2 (D) [MnCl4]2– and [NiF6]2– 2. (i) Paragraph for Question Nos. (i) to (iii) Chemical reactions involve interaction of atoms and molecules. A large number of atoms/molecules (approximately 6.023 × 1023) are present in a few grams of any chemical compound varying with their atomic/molecular masses. To handle such large numbers conveniently, the mole concept was introduced. This concept has implications in diverse areas such as analytical chemistry, biochemistry, electrochemistry and radiochemistry. The following example illustrates a typical case, involving chemical / electrochemical reaction, which requires a clear understanding of the mole concept. A 4.0 molar aqueous solution of NaCl is prepared and 500 mL of this solution is electrolysed. This leads to the evolution of chlorine gas at one of the electrodes (atomic mass : Na = 23, Hg = 200 ; 1 Faraday = 96500 coulombs). [At the anode : 2Cl–  Cl2 + 2e – At the cathode : Na+ + e–  Na Na + Hg  NaHg (sodium amalgam)] (These reactions were not present in IIT-JEE paper) The total number of moles of chlorine gas evolved is : (A) 0.5 (B) 1.0 (C) 2.0 (D) 3.0 (ii) If the cathode is a Hg electrode, the maximum weight (g) of amalgam formed from this solution is : (A) 200 (B) 225 (C) 400 (D) 446 (iii) The total charge (coulombs) required for complete electrolysis is : (A) 24125 (B) 48250 (C) 96500 (D) 193000 Given that the abundances of isotopes 54Fe, 56Fe and 57Fe are 5%, 90% and 5%, respectively, the atomic mass of Fe is : (A) 55.85 (B) 55.95 (C) 55.75 (D) 56.05 3. 4. A student performs a titration with different burettes and finds titre values of 25.2 mL, 25.25 mL, and 25.0 mL. The number of significant figures in the average titre value is : 5. Among the following, the number of elements showing only one non-zero oxidation state is : O, Cl, F, N, P, Sn, Tl, Na, Ti Reaction of Br2 with Na2CO3 in aqueous solution gives sodium bromide and sodium bromate with evolution of CO2 gas. The number of sodium bromide molecules involved in the balanced chemical equation is 6. 7. Dissolving 120 g of urea (mol. wt. 60) in 1000 g of water gave a solution of density 1.15 g/mL. The molarity of the solution is : (A) 1.78 M (B) 2.00 M (C) 2.05 M (D) 2.22 M 8. 29.2% (w/w) HCl stock solution has a density of 1.25 g mL–1. The molecular weight of HCl is 36.5 g mol–1. The volume (mL) of stock solution required to prepare a 200 mL solution of 0.4 M HCl is : An ideal gas in a thermally insulated vessel at intermal pressure = P 1, volume = V1 and absolute temperature = T1 expands irreversibly against zero external pressure, as shown in the diagram. The final internal pressure, volume and absolute temperature of the gas are P2, V2 and T2, respectively. For this expansion, 9. Pext = 0 Pext = 0 (Irreversible) P2,V2,T2 P1, V1, T1 (Thermal insulation) (A) q = 0 (B) T2 = T1 (C) P2V2 = P1V1 (D) P2 V2  P1V1 MOLE CONCEPT 10. If the value of Avogadro number is 6.023 × 1023 mol–1 and the value of Boltzmann constant is 1.380 × 10–23 J k–1. then the number of significant digits in the calculated value of the universal gas constant is 11. A compound H2X with molar weight of 80 g is dissolved in a solvent having density of 0.4 ml–1. Assuming no change in volume upon dissolution, the molality of a 3.2 molar solution is 12. The mole fraction of a solute in a solution is 0.1. At 298K, molarity of this solutions is the same as its molarity. Density of this solutions at 298 K is 2.0 g cm–3. The ratio of the molecular weights of the solute and solvent,  MWsolute    , is  MWsolvent  13. The ammonia prepared by treating ammonium sulphate with calcium hydroxide is completely used by NiCl2.6H2O to form a stable coordination compound. Assume that both the reactions are 100% complete. If 1584 g of ammonium sulphate and 952 g of NiCl2.6H2O are used in the preparation, the combined weight (in grams) of gypsum and the nickel-ammonia coordination compound thus produced is___. (Atomic weights in g mol-1 : H = 1, N = 14, O = 16, S = 32, Cl = 35.5, Ca = 40, Ni = 59) 14. Galena (an ore) is partially oxidized by passing air through it at high temperature. After some time, the passage of air is stopped, but the heating is continued in a closed furnace such that the contents undergo self-reduction. The weight (in kg) of Pb produced per kg of O2 consumed is ______. (Atomic weights in g mol–1 : O = 16, S = 32, pb = 207 15. To measure the quantity of MnCl2 dissolved in an aqueous solution, it was completely converted to KMnO4 using the reaction. MnCl2 + K2S2O8 + H2O  KMnO4 + H2SO4 + HCl (equation not balanced). Few drops of concentrated HCl were added to this solution and gently warmed. Further, oxalic acid (225 mg) was added in portions till the colour of the permanganate ion disappeared. The quantity of MnCl2 (in mg) present in the initial solution is ______. (Atomic weights in g mol–1 : Mn : 55, Cl = 35.5) EXERCISE - 5 : PART # I 1. 2 14. 4 2. 3 15. 2 3. 1 16. 3 4. 4 17. 3 5. 2 6. 1 18. (Bonus) 7. 2 19. 3 8. 3 20. 2 9. 4 10. 1 11. 3 12. 1 13. 4 5 C 21. 3 PART # II 1. B 2. (i) B (ii) D 8. 8 mL. 9. A, B, C 10. 4 (iii) D 11. 8 3. 12. 9 B 13. 2992 4. 3 5. 2 6. 14. 6.47 kg 15. 126 mg 7.