NCERT Class XI Chemistry Some Basic Concepts of Chemistry Solutions
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Question : 34
Total: 36
A welding fuel gas contains carbon and hydrogen only. Burning a small sample of it in oxygen gives 3.38 g carbon dioxide, 0.690 g of water and no other products. A volume of 10.0 L (measured at STP) of this welding gas is found to weigh 11.6 g. Calculate (i) empirical formula, (ii) molar mass of the gas, and (iii) molecular formula.
Solution:
Number of moles of C O 2
No. of moles of C = 0.0768 mole
No. of moles ofH 2 O
No. of moles of H = 2 × 0.0383 = 0.0766 mole
(i) The ratio of moles of C to H is 0.0768 : 0.0766 or 1 : 1
Therefore, empirical formula = CH
(ii) 10.0 L of fuel gas at STP weighs
Molar mass of gas = 25.98 ≈ 26g m o l – 1
(iii) n =
Molecular formula = (Empirical formula)n =( C H ) 2 C 2 H 2
No. of moles of C = 0.0768 mole
No. of moles of
No. of moles of H = 2 × 0.0383 = 0.0766 mole
(i) The ratio of moles of C to H is 0.0768 : 0.0766 or 1 : 1
Therefore, empirical formula = CH
(ii) 10.0 L of fuel gas at STP weighs
Molar mass of gas = 25.98 ≈ 26
(iii) n =
Molecular formula = (Empirical formula)n =
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