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Ch.3 - Molecules and Compounds
Tro - Chemistry: A Molecular Approach 6th Edition
Tro6th EditionChemistry: A Molecular ApproachISBN: 9780137832217Non è quello che usi tu?Cambia libro di testo
Tutti i libri di testoTro 6th EditionCh.3 - Molecules and CompoundsProblema 133
Capitolo 3, Problema 133

A compound of molar mass 177 g/mol contains only carbon, hydrogen, bromine, and oxygen. Analysis reveals that the compound contains eight times as much carbon as hydrogen by mass. Find the molecular formula.

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Identify the elements present in the compound: carbon (C), hydrogen (H), bromine (Br), and oxygen (O).
Let the mass of hydrogen be x grams. According to the problem, the mass of carbon is 8x grams.
Express the mass of each element in terms of moles: \( \text{moles of C} = \frac{8x}{12.01} \), \( \text{moles of H} = \frac{x}{1.008} \).
Assume the remaining mass is due to bromine and oxygen. Let the mass of bromine be y grams and the mass of oxygen be z grams. The total mass is 177 grams, so \( 8x + x + y + z = 177 \).
Use the molar masses to express the moles of bromine and oxygen: \( \text{moles of Br} = \frac{y}{79.90} \), \( \text{moles of O} = \frac{z}{16.00} \).

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Molar Mass

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 masses of all the atoms in a molecule. Understanding molar mass is crucial for determining the number of moles in a given mass of a compound, which is essential for stoichiometric calculations in chemistry.
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Molar Mass Concept

Mass Ratio

The mass ratio is a comparison of the mass of one element to the mass of another element in a compound. In this question, the mass ratio indicates that the mass of carbon is eight times that of hydrogen. This relationship allows us to set up equations to find the relative amounts of each element in the compound, which is vital for deriving the molecular formula.
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Neutron-Proton Ratio

Empirical and Molecular Formulas

The empirical formula represents the simplest whole-number ratio of the elements in a compound, while the molecular formula shows the actual number of atoms of each element in a molecule. To find the molecular formula, one often starts with the empirical formula and uses the molar mass to determine the actual number of atoms. This distinction is important for accurately describing the composition of the compound in question.
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Empirical vs Molecular Formula
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