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MUNISH KAKAR’s INSTITUTE OF CHEMISTRY CHAPTER - BASIC CALCULATIONS IN CHEMISTRY Mole is a chemical unit to measure the quantity of a substance. It is defined as a number which is equal to the number of atoms present in 12gram of C 12 . Mathematically; 1 mole 6.023 10 23 Relationship between Mole and Number of Particles 1 mole of a substance is that quantity of a substance which contains 6.023 x 10 23 (Avogadro number, NA) particles, that is, 1 mole of a substance = NA particles (atoms, molecules, ions). Relationship between Mole and Weight of a Substance 1 mole of a substance is equal to gram atomic weight or gram molecular weight of the substance. For example, 1 mole of oxygen (O) = 16 gm of oxygen, 1 mole of urea (NH2CONH2) = 60 gm of urea and so on. Number of moles of a substance = Weight of a substance GMW/GAW Relation between Mole and Volume of a gas at S.T.P. (T=273 K, P=1.0 atm) Number of moles of a gas = Volume of gas in litre at S.T.P. 22.4 That is, 1 mole of a gas always occupies 22.4 litre at S.T.P. 1 gram atom of an element is equal to its gram atomic weight and 1 gram molecular of a compound is equal to its molecular weight. PROBLEMS Q1. Calculate the number of mole corresponding to; (a) 21.2 g of Na2CO3 ( molecular mass = 106 ) [0.2] (b) 5.4g of Al ( A = 27 ) (c) 4.48 L of H2 [0.2] (e) 6.023 1024 molecules of SO2 [10] (d) 8.96 L of CH4 [0.4] (f) 6.023 1.66 104 g of proton ( mass of 1 proton = 1.66 10 24 g ) Q2. [1 × 10-3] Calculate number of (a) molecules [20] Q3. [0.2] (b) atoms [60] (c) protons in 880 amu of CO2 [440] Calculate number of (a) molecules [0.1 × Nav] (b) atoms [0.3 × Nav] (c) protons in 4.4g of CO2 [2.2 × Nav] Q4. Calculate number of (a) molecules [Same as Q 2] (b) atoms (c) protons in 880 amu of CO2 S.C.O. No. 203, SECOND FLOOR, SECTOR 14, PANCHKULA. Phone : 9417655033, 9888019721 MUNISH KAKAR’s INSTITUTE OF CHEMISTRY Q5. Calculate the mass of Fe (A =56 ) in grams which contains same number of sulphur atoms present in 0.5 mole of Na2S2O3 [56 g] Q6. Calculate the number of atoms of oxygen present in 88 g of CO2. Q7. Methane and SO2 are present in a mixture in the ratio 4:1 by mass. Calculate the ratio of number of molecules of methane and SO2. Q8. [16 : 1] Calculate the number of atoms of helium in each of the following (a) 52 moles of He [52 × Nav] (b) 52 amu of He [13 atoms] Q9. [4 × Nav] (c) 52 g of He [13 × Nav] Calculate how many methane molecules and how many hydrogen and carbon atoms are there in 128 amu of methane. [8 molecules of CH4, 32 atoms of H & 8 atoms of C] Q10. Calculate how many methane molecules and how many hydrogen and carbon atoms are there in 1.6g of methane. [0.1 × Nav CH4 molecules, 0.4 × Nav H atoms, 0.1 × Nav C atoms] Q11. Calculate the total mass of Sodium present in 1.615g mixture of NaCl and NaBr, the mixture is known to contain 36.22% NaCl and rest NaBr. [0.46 g] OBJECTIVE SECTION ( BASIC CALCULATIONS ) Q12. The percentage of Calcium present in CaCO3 (a) 46 (b) 40 (c) 20 (d) 23 Q13. How many molecules are present in one gram of hydrogen ? (a) 6.02 1023 (b) 3.01 1023 (c) 2.5 1023 (d) 1.5 1023 Q14. Which of the following has the least mass? (a) 2 mole of N ( A =14 ) (b) 3 1023 atoms of C (c) 1 mole of S ( A =32 ) (d) 7.0 g of Ag Q15. What is the total number of electrons in 1.0 g of CH4? (a) 0.1 10-23 (b) 4 1023 (c) 0.5 1011 (d) none of these Q16. Number of mole of SO2Cl2 in 13.5 g of SO2Cl2 will be equal to ; (a) 3.2 g of O2 (b) 2.2 g of CO2 (c) 14g of N2 (d) 1.6 g of He ( A =4 ) Q17. The volume occupied by 4.4 g of CO2 at S.T.P. is: (a) 22.4 L (b) 2.24 L (c) 0.224 L (d) 0.1 L Q18. The number of moles of oxygen in 1L of air containing 21% oxygen by volume, in standard conditions is: (a) 0.186 mol (b) 0.21 mol (c) 2.10 mol (d) 0.0093 mol Q19. The number of electrons in 22.4 L of hydrogen gas measured under STP condition are : (a) 6.023 1023 (b) 12.046 1023 (c) 3.0115 1023 (d) zero Q20. The number of water molecules in 1 litre of water is:( where NA represents avogadro's no.) (a) 18 (b) 10 1000 (c) NA (d) 55.55 NA S.C.O. No. 203, SECOND FLOOR, SECTOR 14, PANCHKULA. Phone : 9417655033, 9888019721 MUNISH KAKAR’s INSTITUTE OF CHEMISTRY Q21. The mass of 112 cm3 of CH4 gas at S.T.P. is: (a) 0.16 g (b) 0.8 g (c) 0.08 g (d) 1.6 g Q22. What volume of hydrogen gas, at 273 K and 1 atm pressure will be consumed in obtaining 21.6 g of elemental boron (atomic mass = 10.8 amu) from the reduction of boric oxide (B2O3 ) according to the reaction ; B2O3 H 2 B H 2O ? (a) 32.4 L (b) 18.6 L (c) 67.2 L (d) 32.7 L Q23. 1.5 mol of O2 combine with Mg to form oxide MgO. The mass of Mg (at mass = 24 amu) that has combined is: (a) 72 g (b) 36 g (c) 48 g (d) 24 g Q24. The mass of H2S gas required for 79.5g of CuO is ; (a) 63.5g (b) 17g (c)34g (d) none of these Q25. What volume of oxygen gas under STP will be required for complete combustion 5.2 g of acetylene gas ( C2H2 ) ? a) 3.36 L C2 H 2 ( g ) O2 ( g ) CO2 ( g ) H 2O (l ) b) 112 10 cm 3 3 c) 1.12 dm3 d) none of these Q26. During combustion of unknown gaseous alkane, the volume of CO2 obtained and volume of reacted O2 bears ratio 3 : 5 . The unknown alkane is ; a) C2H6 b) C3H8 c) C5H12 d) C4H10 Q27. The reaction between Aluminium and dilute hydrochloric acid produced H 2 (g) and Al3+ ions. The molar ratio of Aluminium used to hydrogen produced is : (a) 1 : 2 (b) 1 : 3 (c) 2 : 1 (d) 2 : 3 Q28. 2.76 g of silver carbonate (molecular mass 276 amu) is heated strongly, the mass of silver metal obtained is ; ( Ag2CO3 Ag CO2 O2 ) (a) 2.16 (b) 0.216 (c) 216 (d) 21.6 Q29. Assuming fully decomposed, the volume of CO2 released at S.T.P. on heating 9.85 g of BaCO3 (Atomic mass, Ba = 137) will be: ( BaCO3 BaO CO2 ) (a) 0.84 L (b) 2.24 L (c) 4.06 L (d) 1.12 L Q30. Hard water contains 12.00 mg of Mg2+, mole of Na2CO3 required to remove its hardness is: ( Mg 2 Na2CO3 MgCO3 2Na ) (a) 1 4 (b) 5 10 (c) 1 10-3 (d) 12 10-3 Q31. In given question, column - I contains amount of chemical species while column - II contains their respective data. Match contents of Column - I and Column - II appropriately Column-I Column-II S.C.O. No. 203, SECOND FLOOR, SECTOR 14, PANCHKULA. Phone : 9417655033, 9888019721 MUNISH KAKAR’s INSTITUTE OF CHEMISTRY 1 1.6 g of methane A 6.023 1023 molecules B,C,D 2 3.2g of dioxygen D B 6.023 1023 protons. 3 22.4 L NH3 C 6.023 1023 electrons 4 1 mole of molecule D 6.02 10 22 molecules A A STOICHOMETRIC CALCULATIONS Q32. How many mole of HCl will react with 0.8 mole of CaCO3 ? [1.6 mole] CaCO3 2 HCl CaCl2 H 2O CO2 Q33. Calculate mole of oxygen gas which will be used for complete combustion of 2.5 mole of methane. [5 mole] Q34. How mole of hydrogen gas will be liberated when 10.8g of Al is reacted with NaOH ? 2 Al 2 NaOH 2H 2O 2 NaAlO2 3H 2 [0.6 mole] Q35. What mass of Zinc ( A = 65 )on reacting with H2SO4 will liberate 4.48 L of H2 gas under STP condition ? Zn H 2 SO4 ZnSO4 H 2 [13 g] Q36. Calculate the volume of hydrogen gas liberated under STP conditions, when ; (a) 4.8 gram of Mg ( A=24 )is reacted with dilute HCl ( aq.) [4.48 L] (b) 13g of Zn ( A = 65 ) is reacted with NaOH (aq.) [4.48 L] (c) 7.8 g of K (A = 39 ) is reacted with dil. H2SO4 (aq.) [2.24 L] Q37. In commercial manufacture of HNO3, how many number of moles of NO2 produce 7.33 mol HNO3 in the reaction ? 3NO2(g) + H2O(l) 2HNO3(aq) + NO(g) [11.82 mole] Q38. Chlorine is prepared in the laboratory by treating (MnO 2) with aqueous hydrochloric acid according to the reaction : 4HCl(aq) + MnO2(s) 2H2O(l) + MnCl2(aq) + Cl2(g) How many gram of HCl react with 5.0 g of MnO 2? (Atomic mass of Mn=55, O=16, H=1, Cl=35.5 ) [8.614 g] Q39. Calculate the volume of O2 at STP liberated by heating 12.25 g of KClO3. (At. wt. of K=39, 2 KCl (s) 3 O2 ] Cl=35.5, O=16 u). [ 2 KClO3 (s) [3.36 L] S.C.O. No. 203, SECOND FLOOR, SECTOR 14, PANCHKULA. Phone : 9417655033, 9888019721