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NCERT Class XI Chemistry Some Basic Concepts of Chemistry Solutions

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Question : 8 of 36
Marks: +1, -0
Determine the molecular formula of an oxide of iron in which the mass per cent of iron and oxygen are 69.9 and 30.1 respectively.
Solution:  
For empirical formula, Refer Ans. 3
Molecular mass of Fe2O3\mathrm{Fe_2O_3} = 2 × 56 + 3 × 16 = 112 + 48 = 160
Molecular formula = n (Empirical formula)
∴ n = Molecular massEmperical formula mass\frac{\text{Molecular mass}}{\text{Emperical formula mass}} = 160160\frac{160}{160} ⇒ n = 1
∴ Molecular formula = (Fe2O3)(\mathrm{Fe_2O_3}) × 1 = Fe2O3\mathrm{Fe_2O_3}
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