# 3: Composition of Substances and Solutions


Quantitative aspects of the composition of substances and mixtures are the subject of this chapter.

• 3.1: Formula Mass and the Mole Concept
The formula mass of a substance is the sum of the average atomic masses of each atom represented in the chemical formula and is expressed in atomic mass units. The formula mass of a covalent compound is also called the molecular mass. A convenient amount unit for expressing very large numbers of atoms or molecules is the mole. Experimental measurements have determined the number of entities composing 1 mole of substance to be $$6.02214076 \times 10^{23}$$, a quantity called Avogadro’s number.
• 3.2: Conversions Between Grams, Mol, and Atoms (Video)
This video shows the relation ship between grams, mols, and number of atoms of a given sample of an element. Molar mass and Avogadro’s Number are used to convert between these factors.
• 3.3: Determining Empirical and Molecular Formulas
The chemical identity of a substance is defined by the types and relative numbers of atoms composing its fundamental entities (molecules in the case of covalent compounds, ions in the case of ionic compounds). A compound’s percent composition provides the mass percentage of each element in the compound, and it is often experimentally determined and used to derive the compound’s empirical formula.
• 3.4: Determining Empirical and Molecular Formulas from Percent Composition (Video)
The empirical formula of a compound can be obtained from the percent compositions of its elements.  This video discusses the steps required to find an empirical formula from percent compositions.  Also, the molecular formula of a compound can be determined if the molecular weight is given.
• 3.5: Molarity
Solutions are homogeneous mixtures. Many solutions contain one component, called the solvent, in which other components, called solutes, are dissolved. An aqueous solution is one for which the solvent is water. The concentration of a solution is a measure of the relative amount of solute in a given amount of solution. Concentrations may be measured using various units, with one very useful unit being molarity, defined as the number of moles of solute per liter of solution.
• 3.6: Calculations Involving Molarity (Video)
Video shows how to calculate the molarity of a solution.
• 3.7: Calculations Involving Dilution (Video)
Video shows how to calculate the concentration of a diluted solution.
• 3.E: Composition of Substances and Solutions- Homework
These are homework exercises to accompany the Textmap created for "Chemistry" by OpenStax.

## Contributors and Attributions

3: Composition of Substances and Solutions is shared under a CC BY license and was authored, remixed, and/or curated by OpenStax.