b) Given the mass spectrum of benzene, identify the molecular weight and give the molecular formula.

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Understand that a mass spectrum provides information about the mass-to-charge ratio (m/z) of ions. For benzene, the most significant peak corresponds to the molecular ion peak, which indicates the molecular weight.

Identify the molecular ion peak in the mass spectrum. This peak represents the intact molecule of benzene and is typically the highest m/z value among the significant peaks.

Recognize that the molecular weight of benzene corresponds to the m/z value of the molecular ion peak.

Recall the molecular formula of benzene, which is C₆H₆. This formula is derived from the known structure of benzene, a six-carbon ring with alternating double bonds.

Confirm that the molecular weight obtained from the mass spectrum matches the calculated molecular weight of benzene using its molecular formula, C₆H₆.

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Key Concepts

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

Mass Spectrum

A mass spectrum is a graphical representation of the mass-to-charge ratio of ions. It provides information about the molecular weight of compounds by displaying peaks corresponding to different ions, with the highest peak typically representing the molecular ion. Analyzing the spectrum allows chemists to determine the molecular weight and identify the molecular formula of the substance.

Molecular Weight

Molecular weight, or molar mass, is the mass of one mole of a substance, expressed in grams per mole (g/mol). It is calculated by summing the atomic weights of all atoms in a molecule. For benzene (C6H6), the molecular weight can be determined by adding the atomic weights of six carbon atoms and six hydrogen atoms, which is essential for identifying the compound in the mass spectrum.

Molecular Formula

The molecular formula of a compound indicates the number and type of atoms present in a molecule. For benzene, the molecular formula is C6H6, which signifies that each molecule contains six carbon atoms and six hydrogen atoms. Understanding the molecular formula is crucial for interpreting the mass spectrum and confirming the identity of the compound.

Related Practice

Textbook Question

(a) Combustion analysis of 150.0 mg of 1,2,3,benzenetriol, a compound composed of carbon, hydrogen, and oxy-gen, gives 64.3 mg of H2O and 314.2 mg of CO2. What is the empirical formula of 1,2,3,benzenetriol?

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Textbook Question

(a) Combustion analysis of 50.0 mg of benzene, a commonly used solvent composed of carbon and hydrogen, gives 34.6 mg of H₂O and 169.2 mg of CO₂. What is the empirical formula of benzene?

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Textbook Question

Assume that gasoline has the formula C8H18 and has a density of 0.703 g/mL. How many pounds of CO2 are produced from the complete combustion of 1.00 gal of gasoline?

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Textbook Question

Compound X contains only carbon, hydrogen, nitrogen, and chlorine. When 1.00 g of X is dissolved in water and allowed to react with excess silver nitrate, AgNO3, all the chlorine in X reacts and 1.95 g of solid AgCl is formed. When 1.00 g of X undergoes complete combustion, 0.900 g of CO2 and 0.735 g of H2O are formed. What is the empirical formula of X?