Download MUNISH KAKAR`s INSTITUTE OF CHEMISTRY

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  104 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