Ethane and acetylene are two gaseous hydrocarbons. Chemical...

Ethane and acetylene are two gaseous hydrocarbons. Chemical analyses show that in one sample of ethane, $2.65 \mathrm{~g}$ of carbon are combined with $0.665 \mathrm{~g}$of hydrogen, and in one sample of acetylene, $4.56 \mathrm{~g}$ of carbon are combined with $0.383 \mathrm{~g}$ of hydrogen. (a) Are these results consistent with the law of multiple proportions? (b) Write reasonable molecular formulas for these compounds.

Ethane and acetylene are two gaseous hydrocarbons. Chemical analyses show that in one sample of ethane, $2.65 \mathrm{~g}$ of carbon are combined with $0.665 \mathrm{~g}$of hydrogen, and in one sample of acetylene, $4.56 \mathrm{~g}$ of carbon are combined with $0.383 \mathrm{~g}$ of hydrogen.
(a) Are these results consistent with the law of multiple proportions?
(b) Write reasonable molecular formulas for these compounds.

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Key Concepts

Law of Multiple Proportions

This law states that when two elements combine to form more than one compound, the masses of one element that combine with a fixed mass of the other element are in ratios of small whole numbers. It is a fundamental principle in chemistry that supports the idea that compounds form in discrete, consistent proportions, thereby underlining the atomic theory.

Empirical Formula Determination

Determining an empirical formula involves converting the mass of each element present in a compound to moles, and then finding the simplest whole-number ratio of these moles. This process reveals the basic building block of the compound's composition regardless of the actual number of atoms in the molecular unit.

Molecular Formula Determination

Once the empirical formula is known, the molecular formula can be found by comparing the empirical formula mass with the actual molar mass of the compound. The molecular formula is a multiple of the empirical formula and indicates the actual number of atoms of each element in a molecule of the compound.

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