The stimulant amphetamine contains only carbon, hydrogen,...

The stimulant amphetamine contains only carbon, hydrogen, and nitrogen. Combustion analysis of a 42.92 $\mathrm{mg}$ sample of amphetamine gives 37.187 $\mathrm{mg}$ of $\mathrm{H}_{2} \mathrm{O}$ and 125.75 $\mathrm{mg}$ of $\mathrm{CO}_{2}$ . If the molar mass of amphetamine is less than 160 $\mathrm{g} / \mathrm{mol}$ , what is its molecular formula?

Key Concepts

Combustion Analysis

Combustion analysis is a laboratory method used to determine the elemental composition of a compound by burning a sample and measuring the masses of the products such as CO? and H?O. This technique allows for the quantification of elements like carbon and hydrogen since the amounts of CO? and H?O produced can be directly related to the carbon and hydrogen content in the original compound.

Mole Calculations

Mole calculations involve converting measured masses of combustion products into moles using their molar masses. This step is critical in translating the experimental data from combustion analysis into the number of moles of the constituent elements, which forms the basis for determining the compound’s composition.

Empirical Formula Determination

Empirical formula determination is the process of finding the simplest whole-number ratio of atoms of each element in a compound. This is accomplished by comparing the moles of each element derived from the combustion analysis data, thus providing a basic formula that represents the relative proportions of the atoms present.

Molecular Formula Determination

Molecular formula determination uses the empirical formula along with additional molecular mass information to ascertain the actual number of atoms present in a molecule. Once the empirical formula is known, the molecular formula is determined by identifying how many times the empirical formula unit fits into the overall molar mass of the compound.

Mass Balance for Non-Combusted Elements

In combustion analysis involving compounds that contain elements other than carbon and hydrogen, such as nitrogen, the mass balance strategy is used. Since nitrogen does not form a measurable combustion product like CO? or H?O, its amount is determined by subtracting the mass contributions of carbon and hydrogen (derived from CO? and H?O data) from the total mass of the sample.

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