Q. No. 8: Percentage Composition of NaNO₃:
Percentage composition is the mass of each element divided by the total mass of compound. Hence, for this we will need the atomic mass of each element. So,
Sodium = Na = 22.99 g/mol
Nitrogen = N = 14.01 g/mol
Oxygen = O = 16.0 g/mol
Secondly, we will calculate the molar mass of NaNO₃ as,
Molar Mass = (22.99 × 1) + (14.01 × 1) + (16.0 × 3)
Molar Mass = 22.99 + 14.01 + 48
Molar Mass = 85 g/mol
After that we will find the %age of each element as,
%Na = 22.99 / 85 × 100
%Na = 27.04 %
%N = 14.01 / 85 × 100
%N = 16.48 %
%O = 48 / 85 × 100
%O = 56.47 %
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Q. No. 9: Percentage Composition of Ag₂SO₄:
Again the same steps will be followed. The atomic mass of each element is,
Silver = Ag = 107.87 g/mol
Sulfur = S = 32.06 g/mol
Oxygen = O = 16.0 g/mol
Now calculate the molar mass of Ag₂SO₄ as,
Molar Mass = (107.87 × 2) + (32.06 × 1) + (16.0 × 4)
Molar Mass = 215.74 + 32.06 + 64
Molar Mass = 311.8 g/mol
After that we will find the %age of each element as,
%Ag = 215.74 / 311.8 × 100
%Ag = 69.19 %
%S = 32.06 / 311.8 × 100
%S = 10.28 %
%O = 64 / 311.8 × 100
%O = 20.52 %
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Q. No. 10: Mass Percent of water in CuSO₄.5H₂O:
The atomic mass of each element is,
Copper = Cu = 63.55 g/mol
Sulfur = S = 32.06 g/mol
Oxygen = O = 16.0 g/mol
Hydrogen = H = 1.01 g/mol
Now calculate the molar mass of CuSO₄.5H₂O as,
Molar Mass = (63.55 × 1) + (32.06 × 1) + (16.0 × 9) + (1.01 × 10)
Molar Mass = 63.55 + 32.06 + 144 + 10.1
Molar Mass = 249.71 g/mol
The coefficient in CuSO₄.5H₂O specifies that there are 5 moles of water molecules in given hydrate of Copper sulfate, therefore, the mass of 5 moles of water will be,
Mass = Moles × M.Mass
Mass = 5 mol × 18.02 g/mol
Mass = 90.1 g/mol
Hence,
%age of H₂O in CuSO₄.5H₂O is,
%age of H₂O = Mass of H₂O / Mass of CuSO₄.5H₂O × 100
%age of H₂O = 90.1 / 249.71 × 100
%age of H₂O = 36.08 %
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Q. No. 11: Mass of Chlorine in 80.3 g of ZnCl₂:
The atomic mass of each element is,
Zinc = Zn = 65.38 g/mol
Chlorine = Cl = 35.45 g/mol
Now calculate the molar mass of ZnCl₂ as,
Molar Mass = (65.38 × 1) + (35.45 × 2)
Molar Mass = 65.38 + 70.90
Molar Mass = 136.28 g/mol
According to statement,
136.28 g ZnCl₂ contains = 70.9 g Chlorine
So,
80.3 g of ZnCl₂ will contain = X g of Chlorine
Solving for X,
X = 80.3 g × 70.9 g / 136.28 g
X = 41.77 g of Chlorine
