Moles, formulas and concentrations. Master the words chemists use to count atoms they can never see.
These terms were extracted from Chemistry by OpenStax, eCampusOntario (© 2016 Rice University; adapted by BCcampus) which is licensed under a Creative Commons Attribution 4.0 International License.
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experimentally determined value of the number of entities comprising 1 mole of substance, equal to 6.022 × 10²³ mol⁻¹
The relationships between formula mass, the mole, and Avogadro’s number can be applied to compute various quantities that describe the composition of substances and compounds.
sum of the average masses for all atoms represented in a chemical formula; for covalent compounds, this is also the molecular mass
These ideas can be extended to calculate the formula mass of a substance by summing the average atomic masses of all the atoms represented in the substance’s formula.
mass in grams of 1 mole of a substance
The molar mass of an element (or compound) is the mass in grams of 1 mole of that substance, a property expressed in units of grams per mole (g/mol) (see Figure 4).
amount of substance containing the same number of atoms, molecules, ions, or other entities as the number of atoms in exactly 12 grams of ¹²C
This experimental approach required the introduction of a new unit for amount of substances, the mole, which remains indispensable in modern chemical science.
sum of average atomic masses for all atoms represented in an empirical formula
Molecular formulas are derived by comparing the compound’s molecular or molar mass to its empirical formula mass.
percentage by mass of the various elements in a compound
The results of these measurements permit the calculation of the compound’s percent composition, defined as the percentage by mass of each element in the compound.
solution for which water is the solvent
A solution in which water is the solvent is called an aqueous solution.
qualitative term for a solution containing solute at a relatively high concentration
Solute concentrations are often described with qualitative terms such as dilute (of relatively low concentration) and concentrated (of relatively high concentration).
quantitative measure of the relative amounts of solute and solvent present in a solution
The relative amount of a given solution component is known as its concentration.
qualitative term for a solution containing solute at a relatively low concentration
Solute concentrations are often described with qualitative terms such as dilute (of relatively low concentration) and concentrated (of relatively high concentration).
process of adding solvent to a solution in order to lower the concentration of solutes
Dilution is the process whereby the concentration of a solution is lessened by the addition of solvent.
describes the process by which solute components are dispersed in a solvent
This component is called the solvent and may be viewed as the medium in which the other components are dispersed, or dissolved.
unit of concentration, defined as the number of moles of solute dissolved in 1 liter of solution
Molarity (M) is a useful concentration unit for many applications in chemistry.
solution component present in a concentration less than that of the solvent
A solute is a component of a solution that is typically present at a much lower concentration than the solvent.
solution component present in a concentration that is higher relative to other components
This component is called the solvent and may be viewed as the medium in which the other components are dispersed, or dissolved.