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Ch.3 - Mass Relationships in Chemical Reactions
Chapter 3, Problem 93

An unknown liquid is composed of 34.31% C, 5.28% H, and 60.41% I. The molecular weight found by mass spectrometry is 210.06. What is the molecular formula of the compound?

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Empirical Formula

The empirical formula represents the simplest whole-number ratio of the elements in a compound. To determine it, the percentage composition of each element is converted to moles, and then the ratios are simplified. This formula provides a foundational understanding of the compound's composition before deriving the molecular formula.
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Empirical vs Molecular Formula

Molecular Weight

Molecular weight, or molar mass, is the mass of one mole of a substance, typically expressed in grams per mole (g/mol). It is calculated by summing the atomic weights of all atoms in the molecular formula. In this question, the molecular weight obtained from mass spectrometry (210.06 g/mol) is crucial for determining the molecular formula from the empirical formula.
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Weight Conversion Example

Molecular Formula

The molecular formula indicates the actual number of atoms of each element in a molecule of a compound. It can be derived from the empirical formula by multiplying the subscripts by a whole number, which is determined by dividing the molecular weight by the empirical formula weight. This formula provides a complete picture of the compound's composition.
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Determining Molecular Formulas