Chemical Arithmetics

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Empirical formula is the simplest whole-number ratio of atoms of each element in a compound. It does not show the actual number of atoms but gives the relative proportions. For example, the empirical …

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Molecular formula shows the actual number of atoms of each element in a molecule. It is a whole-number multiple of the empirical formula. For example, benzene has molecular formula C₆H₆ and empirical …

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Molecular formula = n × Empirical formula, where n is a positive integer. For example, acetic acid has molecular formula C₂H₄O₂ and empirical formula CH₂O, so n = 2.

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Ionic compounds exist as crystal lattices made of repeating ions, not discrete molecules. Therefore, they are represented by empirical formulas showing the simplest ion ratio. NaCl means Na⁺ and Cl⁻ i…

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Molar mass of CH₄ = 12 + 4×1 = 16 g/mol Mass of C = 12 g % C = (12 / 16) × 100 = 75% Answer: 75%…

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Molar mass of H₂O = 2×1 + 16 = 18 g/mol Mass of O = 16 g % O = (16 / 18) × 100 = 88.89% Answer: 88.89%…

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Assume 100 g sample: C: 40 g → 40/12 = 3.33 mol H: 6.67 g → 6.67/1 = 6.67 mol O: 53.33 g → 53.33/16 = 3.33 mol Divide by smallest (3.33): C: 1, H: 2, O: 1 Empirical formula: CH₂O…

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Assume 100 g sample: Al: 52.9 g → 52.9/27 = 1.96 mol O: 47.1 g → 47.1/16 = 2.94 mol Divide by smallest (1.96): Al: 1, O: 1.5 → Multiply by 2: Al₂O₃ Empirical formula: Al₂O₃…