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When studying chemistry, one often needs to convert the mass of a substance to the number of moles, as this links the amount of substance to its molecular or atomic scale. The conversion from grams to moles is straightforward but critical in stoichiometry.

To make this conversion, you must know the molar mass of the substance, which is the mass in grams of one mole of that substance. The molar mass serves as a conversion factor between grams and moles. Here's the general formula you can use:

\[ \text{Number of moles} = \frac{\text{given mass in grams}}{\text{molar mass in g/mol}} \]

Taking our ethane example from the exercise, the calculation shows that 0.334 grams of ethane is equivalent to 0.0111 moles. Always ensure the units are correct to avoid any mistakes in the conversion.

Avogadro's number is a fundamental concept in chemistry, representing the quantity of particles (whether atoms, molecules, ions, or others) in one mole of a substance. The value of Avogadro's number is fixed at \(6.022 \times 10^{23}\). This number is incredibly large because atoms and molecules are extremely small.

Utilizing Avogadro's number allows us to count the particles in a given amount of moles. To convert moles to number of particles, we multiply the number of moles by Avogadro's number:
\[ \text{Number of particles} = \text{Number of moles} \times \text{Avogadro's number} \]

Returning to our example, from the 0.0111 moles of ethane calculated earlier, we can determine there are approximately \(6.68 \times 10^{22}\) molecules of ethane in the 0.334 grams sample.

Understanding the molecular composition of a compound involves knowing which atoms are present and in what quantities. You need to be familiar with the element symbols, such as C for carbon and H for hydrogen, as well as the molecular formula that indicates the ratio of atoms in a molecule.

In our exercise, ethane has the molecular formula \(\text{C}_{2}\text{H}_{6}\), which means each molecule consists of two carbon atoms and six hydrogen atoms. The molecular composition helps to establish the molar mass of the compound by adding up the molar masses of all the individual atoms calculated by multiplying the quantity of each atom with its atomic molar mass.

Knowing the molecular composition not only aids in the calculation of molar mass but is also essential in understanding the chemical properties and reactions of the molecule.