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Home Glossary

# Glossary: The mole concept

Glossary
aliquot.
A sample of precisely determined amount taken from a material.

alkalinity.
A measure of a material's ability to neutralize acids. Alkalinities are usually determined using titration.

Italian chemist and physicist Amadeo Avogadro (1776-1856) proposed a correct molecular explanation for Gay-Lussac's law of combining volumes. His work provided a simple way to determine atomic weights and molecular weights of gases.

The number of particles in one mole, equal to 6.02214199 × 1023 mol-1 (± 0.00000047 mol-1) [1998 CODATA values]

empirical formula. simplest formula. Compare with molecular formula.
Empirical formulas show which elements are present in a compound, with their mole ratios indicated as subscripts. For example, the empirical formula of glucose is CH2O, which means that for every mole of carbon in the compound, there are 2 moles of hydrogen and one mole of oxygen.

experimental yield. actual yield. Compare with theoretical yield and percent yield.
The measured amount of product produced in a chemical reaction.

formula weight. formula mass. Compare with molecular weight and empirical formula.
The formula weight is the sum of the atomic weights of the atoms in an empirical formula. Formula weights are usually written in atomic mass units (u).

formula unit. Compare with empirical formula.
One formula weight of a compound.

limiting reactant. limiting reagent.
The reactant that limits the amount of product produced in a chemical reaction. For example, mixing one mole of H2(g) with one mole of O2 produces one mole of steam (H2O(g)), with half a mole of O2(g) remaining. The hydrogen gas limits the amount of steam produced in this case.

mass percentage. ((w/w)%)
Mass percentages express the concentration of a component in a mixture or an element in a compound. For example, household bleach is 5.25% NaOCl by mass, meaning that every 100 g of bleach contains 5.25 g of NaOCl. Mass percentage can be calculated as 100% times the mass of a component divided by the mass of the mixture containing the component.

molar.
1. Of or pertaining to moles. 2. An synonym for molarity; for example, a "six molar solution of hydrochloric acid" contains 6 moles of HCl per liter of solution.

molarity. (M) molar concentration.
Concentration of a solution measured as the number of moles of solute per liter of solution. For example, a 6 M HCl solution contains 6 moles of HCl per liter of solution.

mole. (mol)
SI unit for amount of substance, defined as the number of atoms in exactly 12 g of carbon-12. One mole of a molecular compound contains Avogadro's number molecules and has a mass equal to the substance's molecular weight, in grams.

molecular formula. formula; chemical formula. Compare with empirical formula.
A notation that indicates the type and number of atoms in a molecule. The molecular formula of glucose is C6H12O6, which indicates that a molecule of glucose contains 6 atoms of carbon, 12 atoms of hydrogen, and 6 atoms of oxygen.

molecular weight. molecular mass. Compare with formula weight and molecular formula.
The average mass of a molecule, calculated by summing the atomic weights of atoms in the molecular formula. Note that the words mass and weight are often used interchangeably in chemistry.

mole. (mol)
The mole is the SI unit for amount of substance. 1 mole of particles is equal to the number of atoms in exactly 12 g of carbon-12. 1 mole of molecules has a mass equal to the molecular weight in grams.

percent yield. percentage yield. Compare with theoretical yield and actual yield.
Percent yield equals experimental yield divided by theoretical yield times 100%.

theoretical yield. maximum yield; stoichiometric yield. Compare with actual yield and percent yield.
The amount of product obtained when all of the limiting reagent reacts.

volume percentage. ((v/v)%)
Volume percentages express the concentration of a component in a mixture or an element in a compound. For example, 95% ethanol by volume contains 95 mL of ethanol in 100 mL of solution (NOT in 100 mL of water!)

yield. experimental yield; actual yield. Compare with theoretical yield and percent yield.
The amount of product actually obtained in a chemical reaction.

General Chemistry Online! The mole concept