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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*.

Avogadro. Amadeo Avogadro.
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.

Avogadro number. (NA, L) Avogadro's number; Avogadro constant.
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

Copyright © 1997-2010 by Fred Senese
Comments & questions to fsenese@frostburg.edu
Last Revised 08/17/15.URL: http://antoine.frostburg.edu/chem/senese/101/moles/glossary.shtml