Mole Concept Exercise # 4

MOLE CONCEPT Exercise # 4 [Subjective Type Questions] 1. 1.375 g of cupric oxide was reduced by heating in a current of hydrogen and the weight of copper obtained was 1.098 g. In another experiment, 1.179 g of copper was dissolved in nitric acid and the resulting solution was evaporated to dryness. The residue of copper nitrate when strongly heated was converted into 1.4476 g of cupric oxide. Show that the results are in agreement with the law of constant proportion. 2. Elements X and Y from two different compounds. In the first 0.324 g of X is combined with 0.471 g of Y. In second, 0.117 g of X is combined with 0.509 g of Y. Show that these data illustrate the law of multiple proportions. 3. How many g of element are present in 35.125 g atom of Si. (Given at. wt. of Si = 28.) 4. Calculate the no. of molecules in a drop of water weighing 0.07 g. 5. Calculate no. of each atom present in 106.5 g of NaClO3. 6. Find the no. of mole of phosphorus in 92.9 g of phosphorus assuming that molecular formula of phosphorus in P4. Also determine the no. of atoms and molecules of phosphorus in the sample. 7. Calculate the number of moles in 5.75 g of sodium. (Atomic mass of sodium = 23.) 8. How many grams of each of the following elements must be taken to get 1 mol of the element? (a) Sodium (b) Chlorine (c) Copper 3 9. The density of liquid mercury is 13.6 / cm . How many moles of mercury are there in 1 litre of the metal ? (Atomic mass of Hg = 200) 10. 50 g of CaCO3 is allowed to react with 70 g of H3PO4. Calculate : (i) 11. amount of Ca3 (PO4)2 formed (ii) amount of unreacted reagent N2H4, Hydrazine a rocket fuel can be produced according to the following reaction : ClNH2 + 2NH3 N2H4 + NH4Cl When 1000 g ClNH2 is reacted with excess of NH3, 473 g N2H4 is produced. What is the % yield of the reaction. 12. Carbon disulphide 'CS2', can be made from by product SO2. The overall reaction is 5C + 2SO2  CS2 + 4CO How much CS2 can be produced from 450 kg of waste SO2 with excess of coke if the SO2 conversion is 82%. 13. Calculate the percent of BaO in 29.0 g of a mixture of BaO and CaO which just reacts with 100.8 mL of 6.00 M HCl. BaO + 2HCl BaCl2 + H2O CaO + 2HCl CaCl2 + H2O 14. Calculate the amount of 95% pure Na2CO3 required to prepare 5 litre of 0.5 M solution. 15. Calculate the molality of a sulphuric acid solution of specific gravity 1.2 containing 27% H 2SO 4 by weight. 16. A gaseous alkane is exploded with oxygen. The moles of O2 for complete combustion and CO2 formed is in the ratio 7 : 4. Deduce molecular formula of alkane. 17. When 2.86 g of a mixture of 1-butene, C 4 H 8 and butane C 4 H 10 was burned in excess of oxygen, 8.80 g of CO2 and 4.14 g of H2O were obtained. What is percentage by mass of butane in the mixture. 18. If v mL of a gaseous hydrocarbon, after explosion with excess of oxygen, showed a contraction of 2.5 v mL and a further contraction of 2v mL with caustic potash, Find the formula of hydrocarbon. 19. The average mass of one gold atom in a sample of naturally occuring gold is 3.2707 × 10 the molar mass of gold. 20. A plant virus is found to consist of uniform symmetrical particles of 150 Å in diameter and 5000 Å long. The specific 3 volume of the virus is 0.75 cm /g. If the virus is considered to be a single particle, find its molecular weight. 21. Density of a gas relative to air is 1.17. Find the mol. mass of the gas [Mair = 29 g/mol] 22. One type of artificial diamond (commonly called YAG for yttrium aluminium garnet) can be represented by the formula Y3Al5O12. –22 g. Use this to calculate (a) Calculate the weight percentage composition of this compound. (b) What is the weight of yttrium present in a 200 – carat YAG if 1 carat - 200 mg ? (Y = 89, Al = 27) 23. A chemical commonly called "dioxin" has been very much in the news in the past few years. (It is the by product of herbicide manufacture and is thought to be quite toxic.) Its formula is C 12 H 4 Cl 4 O 2 . If you –4 have a sample of dirt (28.3 g) that contains 1.0 × 10 % dioxin, how many moles of dioxin are in the dirt sample? 24. A chemist wants to prepare diborane by the reaction 6 LiH + 8 BF3  6 Li BF4 + B2H6 If the starts with 2.0 moles each of LiH & BF3. How many moles B2H6 can be prepared. 25. One gram of an alloy of aluminium and magnesium when heated with excess of dil. HCl forms magnesium chloride, aluminium chloride and hydrogen. The evolved hydrogen collected over mercury at 0°C has a volume of 1.2 litres at 0.92 atm pressure. Calculate the composition of the alloy. 26. A 10 g sample of a mixture of calcium chloride and sodium chloride is treated with Na2CO3 to precipitate calcium as calcium carbonate. This CaCO3 is heated to convert all the calcium to CaO and the final mass of CaO is 1.62 g. Calculate % by mass of NaCl in the original mixture. 27. By the reaction of carbon and oxygen, a mixture of CO and CO2 is obtained. What is the composition of the mixture by mass obtained when 20 grams of O2 reacts with 12 grams of carbon ? 28. The action of bacteria on meat and fish produces a poisonous compound called cadaverine. As its name and origin imply, it stinks ! It is 58.77% C, 13.81 % H, and 27.42 % N. Its molar mass is 102 g/mol. Determine the molecular formula of cadaverine. 29. Given the following empirical formulae and molecular weight, compute the true molecular formulae : Empirical formula 30. Molecular weight (a) CH2 84 (b) CH2O 150 (c) HO 34 (d) (e) HgCl HF 472 80 What is the percentage of nitrogen in an organic compound 0.14 g of which gave by Dumas method 82.1 c.c. of nitrogen collected over water at 27°C and at a barometric pressure of 774.5 mm? (aqueous tension of water at 27°C is 14.5 mm) MOLE CONCEPT 31. Calculate the molarity of the following solutions : (a) 4g of caustic soda is dissolved in 200 mL of the solution. (b) 5.3 g of anhydrous sodium carbonate is dissolved in 100 mL of solution. (c) 0.365 g of pure HCl gas is dissolved in 50 mL of solution. 32. A mixture of ethanol and water contains 54 % water by mass. Calculate the mole fraction of alcohol in this solution. 33. 10 mL of a mixture of CO, CH4, and N2 exploded with excess of oxygen gave a contraction of 6.5 mL. There was a further contraction of 7 mL, when the residual gas treated with KOH. What is the composition of the original mixture? 34. When 100 mL of a O2 – O3 mixture was passed through turpentine, there was reduction of volume by 20 mL. If 100 mL of such a mixture is heated, what will be the increase in volume? 35. A crystalline hydrated salt on being rendered anhydrous, loses 45.6% of its weight. The percentage composition of anhydrous salt is : Al = 10.5%, K = 15.1%, S = 24.8% and I = 49.6%. Find the empirical formula of the anhydrous and crystalline salt : 36. How much quantity of zinc will have to be reacted with excess of dilute HCl solution to produce sufficient hydrogen gas for completely reacting with the oxygen obtained by decomposing 5.104 g of potassium chlorate? 37. A 1.85 g sample of mixture of CuCl 2 and CuBr 2 was dissolved in water and mixed thoroughly with 1.8 g portion of AgCl. After reaction, the solid which now contain AgCl and AgBr was filtered, dried and weighed to be 2.052 g. What was the % by weight of CuBr2 in the mixture? 38. 1.0 g of a sample containing NaCl, KCl and some inert impurity is dissolved in excess of water and treated with excess of AgNO3 solution. A 2.0 g precipitate to AgCl separate out. also sample is 23% by mass in sodium. Determine mass percentage of KCl in the sample : 39. A mixture of CuSO4 . 5H2O and MgSO4 . 7H2O was heated until all the water was driven-off. If 5.0 g of mixture gave 3 g of anhydrous salts, what was the percentage by mass of CuSO4 . 5H2O in the original mixture : 40. A compound containing Ca, C, N and S was subjected to quantitative analysis and formula mass determination. A 0.25 g of this compound was mixed with Na 2 CO 3 to convert all Ca into 0.16 g CaCO 3 . A 0.115 g sample of compound was carried through a series of reactions until all its S was changed into SO 42 and precipitated as 0.344 g of BaSO4 . A 0.712 g sample was processed to liberate all of its N as NH3 and 0.155 g NH3 was obtained. The formula mass was found to be 156. Determine the empirical and molecular formula of the compound 41. A 0.2 g sample, which is mixture of NaCl, NaBr and NaI was dissolved in water and excess of AgNO3 was added. The precipitate containing AgCl, AgBr and AgI was filtered, dried and weighed to be 0.412 g. The solid was placed in water and treated with excess of NaBr, which converted all AgCl into AgBr. The precipitate was then weighed to be 0.4881 g. It was then placed into water and treated with excess of NaI, which converted all AgBr into AgI. The precipitate was then weighed to be 0.5868 g. What was the percentage of NaCl, NaBr and NaI in the original mixture : 42. 2.5 g of a sample containing Na2CO3 ; NaHCO3 and some non-volatile impurity on gentle heating loses 12% of its weight. Residue is dissolved in 100 mL water and its 10 mL portion required 15 mL 0.1 M aqueous solution of BaCl2 for complete precipitation of carbonates. Determine mass percentage of Na2CO3 in the original sample ? 43. Based on the following information, determine value x and y : AgNO 3 (CH 3 )x AlCly  xCH 4 (g)  yCl  Al3    AgCl(s) 0 .64 3 g 0 .22 2 g 0 .996 g 44. A 5.0 g sample of felspar containing Na2O, K2O and some inert impurity is dissolved in dilute HCl solution and NaCl and KCl formed are separated by fractional crystallization. During crystallization some less soluble impurities also comes out. Mass of NaCl, KCl and impurity accompanying these salts was found to be 6.47 g. Solid crystal was then re-dissolved and required 300 mL of 0.3 M AgNO3 for complete precipitation of chlorides. The precipitate this, obtained was found to contain 4.23 % insoluble impurity. Determine mass percentage of Na2O and K2O in the original sample : 45. Pb(NO3)2 and KI reacts in aqueous solution to form an yellow precipitate of PbI2. In one series of experiments, the masses of two reactants varied, but the total mass of the two was held constant at 5.0 g. What maximum mass of PbI2 can be produced in the above experiment : 46. Uranium is isolated from its ore by dissolving it as UO2 (NO3)2 and separating it as solid UO2(C2O4). xH2O. A 1.0 g sample of ore on treatment with nitric acid yielded 1.48 g UO2 (NO3)2 which on further treatment with 0.4 g Na2C2O4 yielded 1.23 g UO2 (C2O4).xH2O. Determine weight percentage of uranium in the original sample and x : 47. A mother cell disintegrate into sixty identical cells and each daughter cell further disintegrate into 24 smaller cells. The smallest cells are uniform cylindrical in shape with diameter of 120 Å and each cell is 6000 Å long. Determine molar mass of the mother cell if density of the smallest cell is 1.12 g/cm3 : 48. A sample is a mixture of Mohr's salts and (NH4)2SO4. A 0.5 g sample on treatment with excess of BaCl2 solution gave 0.75 g BaSO4. Determine percentage composition of the salt mixture . What weight of Fe2O3 would be obtained if 0.2 g of the sample were ignited in air ? 49. A chloride mixture is prepared by grinding together pure BaCl2.2H2O, KCl and NaCl. What is the smallest and largest volume of 0.15 M AgNO3 solution that may be used for complete precipitation of chloride from a 0.3 g sample of the mixture which may contain any one or all of the constituents ? 50. One mole of a mixture of N2, NO2 and N2O4 has a mean molar mass of 55.4. On heating to a temperature at which N2O4 may be dissociated : N2O4 2NO2, the mean molar mass tends to the lower value of 39.6. What is the mole ratio of N2 : NO2 : N2O4 in the original mixture? 51. 10 mL of gaseous organic compound contain C, H and O only was mixed with 100 mL of O2 and exploded under identical conditions and then cooled. The volume left after cooling was 90 mL. On treatment with KOH a contraction of 20 mL was observed, if vapour density of compound is 23 derive molecular formula of the compound. 52. Fluorocarbon polymers can be made by fluorinating polyethylene according to the reaction (CH 2)n + 4nCoF3  (CF2)n + 2nHF + 4nCoF2, where n is a large integer. The CoF3 can be regenerated by the reaction 2 CoF2 + F2  2CoF3. If the HF formed in the first reaction cannot be reused, how many kg of fluorine are consumed per kg of fluorocarbon produced, (CF2)n? If HF can be recovered and electrolyzed to hydrogen and flurine, and if this fluorine is used for regenerating CoF3, what is the net consumption of fluorine per kg of fluorocarbon? 53. A2 + 2B2  A2B4 3 A + 2B2  A3B4 2 2 Two substance A2 & B2 react in the above manner when A2 is limited it gives A2B4 in excess gives A3B4. A2B4 can be converted to A3B4 when reacted with A2. Using this information calculate the composition of the final mixture when the mentioned amount of A & B are taken :c (a) 4 moles A2 & 4 moles B2 1 moles A2 & 2 moles B2 2 (c) 1.25 moles A2 & 2 moles B2 (b) MOLE CONCEPT 54. In a water treatment plant, Cl2 used for the treatment of water is produced from the following reaction 2KMnO4 + 16HCl  2KCl + 2MnCl2 + 8H2O + 5Cl 2. If during each feed 1 L KMnO4 having 79% (w/v) KMnO4 & 9 L HCl with d = 1.825 g/mL & 10% (w/w) HCl are entered & if that percent yield is 80% then calculate : (a) amount of Cl2 produced. (b) amount of water that can be treated by Cl2 if 1 litre consumes 28.4 g of Cl2 for treatment. (c) calculate efficiency  of the process if  = vol.of water treated vol.of totalfeed 3 55. A sea water sample has a density of 1.03 g/cm and 2.8% NaCl by mass. A saturated solution of NaCl in water is 5.45 M NaCl. How much water would have to be evaporated from 1.00 × 106 L of the sea water before NaCl would precipitate ? 56. A sample of oleum is such that ratio of "free SO3" by "combined SO3" is equal to unity. Calculate its labelling in terms of percentage oleum. 57. 3 One litre of milk weighs 1.035 kg. The butter fat is 4% (v/v) of milk has density of 875 kg/m . Find the density of fat free skimed milk. 58. A sample of fuming sulphuric acid containing H2SO4, SO3 and SO2 weighing 1.00 g is found to require 23.47 mL of 1.00 M alkali (NaOH) for neutralisation. A separate sample shows the presence of 1.50% SO 2. Find the percentage of "free" SO3, H2SO4 and "combined" SO3 in the sample. 59. In one process for waterproofing, a fabric is exposed to (CH3)2SiCl2 vapour. The vapour reacts with hydroxyl groups on the surface of the fabric or with traces of water to form the waterproofing film [(CH3)2SiO]n, by the reaction – n(CH3)2SiCl2 + 2nOH 2nCl + nH2O + [(CH3)2SiO]n where n stands for a large integer. The waterproofing film is deposited on the fabric layer upon layer. Each layer is 6.0 Å thick [the thickness of the (CH3)2SiO group]. How much (CH3)2SiCl2 in needed to waterproof one side of a piece of fabric, 1.00 m by 3.00 m, with a film 300 layers thick ? The density of the film is 1.0 g/cm3. 60. 20 mL of a mixture of methane and a gaseous compound of Acetylene series were mixed with 100 mL of oxygen and exploded. The volume of the products after cooling to original room temperature and pressure, was 80 mL and on treatment with potash solution a further contracting of 40 mL was observed. Calculate (a) the molecular formula of the hydrocarbon, (b) the percentage composition of the mixture. 61. In a solution the concentration of CaCl2 is 5 M & that of MgCl2 is 5 m. The specific gravity of solution is 1.05, – calculate the concentration of Cl in the solution in terms of Molarity.