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Empirical or molecular formula from percentage composition

This type of question, asked 6 times: 28 Jun 2022, 25 Jan 2023, 5 Apr 2024, 24 Jan 2025, 28 Jan 2025, 6 Apr 2026 S1. All 7 questions below, oldest first.

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  1. Question 1

    28 Jun 2022

    121
    Compound A contains 8.7%8.7\% Hydrogen, 74%74\% Carbon and 17.3%17.3\% Nitrogen. The molecular formula of the compound is, Given: Atomic masses of C, HH and NN are 12, 1 and 14 amu respectively. The molar mass of the compound A is 162 g mol−1162\text{ }g{\text{ }mol}^{- 1}.

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  2. Question 2

    25 Jan 2023

    143
    Number of hydrogen atoms per molecule of a hydrocarbon A having 85.8%85.8\% carbon is (Given: Molar mass of A=84 g mol−1A = 84\text{ }g{\text{ }mol}^{- 1} )

  3. Question 3

    5 Apr 2024

    47
    An organic compound has 42.1%42.1\% carbon, 6.4%6.4\% hydrogen and remainder is oxygen. If its molecular weight is 342 , then its molecular formula is :

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  4. Question 4

    24 Jan 2025

    124
    The hydrocarbon (X) with molar mass 80 g mol−180\text{ }g{\text{ }mol}^{- 1} and 90%90\% carbon has ______\_\_\_\_\_\_ degree of unsaturation.

  5. Question 5

    24 Jan 2025

    111
    The elemental composition of a compound is 54.2%54.2\% C, 9.2%9.2\% H and 36.6%O36.6\% O. If the molar mass of the compound is 132 g mol−1132\text{ }g{\text{ }mol}^{- 1}, the molecular formula of the compound is : [Given : The relative atomic mass of C:H:O=C:H:O = 12:1:16]12:1:16\rbrack

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  6. Question 6

    28 Jan 2025

    47
    Quantitative analysis of an organic compound (X) shows following % composition. C : 14.5% Cl : 64.46% H: 1.8%, the rest being oxygen. The empirical formula mass of the compound (X) is _____\_\_\_\_\_ ×10−1\times10^{- 1} (Given molar mass in gmol−1gmol^{- 1} of C:12,H:1C:12,H:1, O:16,Cl:35.5)O:16,Cl:35.5)

  7. Question 7

    6 Apr 2026 S1

    26
    An oxide of iron contains 69.9%69.9\% iron, its empirical formula, is : (Given : Molar mass of Fe and O are 56 and 16 g mol−116\text{ }g{\text{ }mol}^{- 1} respectively.)

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