The mole represents the chemical amount of a substance. Regardless of the nature of the substance a mole contains Avagadro's number of atoms, molecules or formula units. Thus the mole allows us to count entities by weighing them.
You will learn to convert mass and number to moles and vice versa. You will also learn to calculate the mass % of an element in a compound, as well as the mass in of an element in a given amount of a compound.
The percent composition of a compound is defined. It is easy to calculate if we know the chemical formula of the compound. However, the reverse problem is ambiguous, and we can only the obtain the empirical formula.
To prepare for this lecture, please read sections 3.1 through 3.5 of Zumdahl
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