Posts Tagged ‘Mole’
The chemical counting unit or chemists’ unit, Mole, is that amount of a substance which contains as many entities (atoms, molecules, ions or other species) as there are atoms in exactly 0.12 Kg (or 12 g) of the carbon -12 isotope. The word ‘mole’ was introduced around 1896 by Wilhelm Ostwald who derived the term from Latin word moles meaning a ‘heap or pile’ considering a substance as a heap of atoms or molecules. The unit ‘Mole’ was accepted in 1967 in order to provide a simple way of reporting a large number such as those of atoms, molecules and subatomic particles. The mole of a substance always contains the same number of entities irrespective of the identity and kind of the substance.
This no is so important that it has been given a separate name and symbol viz. Avogadro constant or Avogadro number, denoted by NA in honor of the nineteenth century Italian scientist, Amedeo Avogadro. Though this quantity is known to seven significant figures, in most calculations the value, 6.022137×1023 entities/mol for NA is generally used. Whereas a mol is a convenient unit for expressing the amount of species like atoms, molecules, ions etc., it is not a useful unit for larger species as it contains a huge number of species. The relationship between number of species and their masses has proved to be very useful and meaningful for chemists. Moreover being a S. I. Unit it can be used with a prefix also. For example, 1 m mol., 1? mol and 1n mol are equal to 10-3 mol, 10-6 mol, and 10-9 mol. respectively. The number of species may be converted into mol and vice-versa by using Avogadro number. While 1 mol of different substances will contain the same number of particular species, it will have different masses for different substances.
Mole Day was created as a way to foster interest of students in chemistry. Many schools throughout the world celebrate Mole Day with various activities related to chemistry and/or moles. The relationship between Mole and Avogadro Number was first discovered by Amedeo Avogadro but he received credit for this work after his death. In the early 1980’s an article appeared in ‘The Science Teacher’ about a high school chemistry teacher and her rational for the idea of celebrating the day. With this small article, the seed was planted for establishing a national organization. On May 15, 1991, the National Mole Day Foundation (NMDF) was born. News releases were sent to the regional and national news media, especially the chemical science news media, announcing the formation of the Foundation. The purpose of the National Mole Day Foundation was and continues to be to get all persons, especially students, enthused about chemistry. As interest in the NMDF has now grown, the organization of the Foundation has developed. The NMDF is completely self-supporting through membership fees and the sale of t-shirts and other merchandise. One big reason the Foundation is able to generate so much interest is that each year a different national theme is chosen. To go along with that special theme each year, two caricature/icon mascots are developed. Starting in 1993, a professionally recorded theme song has accompanied the fall newsletter mailing.
1993 was also the first in another way as well. At the ChemEd ‘93 conference at Butler University, the newly established “National Mole of the Year” Award was first presented. This award has continued with presentations at ChemEd ‘95 at Old Domini-++on University and ChemEd ‘97 at the University of Minnesota. It is really the “Mole-of-the-Every-Other Year” because the award is presented at the ChemEd Conferences which are only held in odd numbered years. In summary, the NMDF was created with the intention to get everyone, especially kids, enthused about chemistry. Since the National Mole Day Foundation was created in May of 1991 by Maurice Oehler, now a retired high school chemistry teacher from Prairie du Chien, WI, the membership has soared.
Lorenzo Romano Amedeo Carlo Avogadro, known as Amedeo Avogadro, was born in 1776. Possibly of aristocratic descent, he was a lawyer until he decided to devote himself to one of his other interests. In his late twenties he was appointed to the first chair in mathematical physics in Italy, at L’ Universita` di Torino. Avogadro was the first to publish the idea that elements could exist as molecules. He died in 1856 but his contribution to science was not recognized until 1860, when Stanislao Cannizzaro, a co-national who for many years had been teaching a course of lectures on why Avogadro had been wrongfully ignored, was persuaded to propound his views at a conference in Karlsruhe, Germany. The basis for the number named after Avogadro is the number of atoms of 12Carbon in 12 grams of 12Carbon.
Aamadeo Avogadro was actually a physics professor but he experimented in both physics and chemistry using mathematics to base most of his findings. Avogadro is well known for his hypothesis known as Avogadro’s Law. His law simply states that at a fixed temperature and pressure, equal volumes of gases contain the same number of molecules. Avogadro received no recognition for his hypothesis or his constant during his lifetime because he was not considered as a brilliant experimenter but rather, a careless one. He also did not back up his hypothesis with an impressive display of experimental results. He also did not have an impressive reputation for accurate experimental work. Another reason why his hypothesis was not recognized was the fact that his work was published in obscure journals. Moreover he remained isolated from the mainstream of chemistry done in his time. Two years after his death, a colleague, Stanislao Cannizzaro (1826-1910) showed how the use of Avogadro’s number could solve many of the problems in chemistry. This time Avogadro’s paper was looked at more carefully over a wider and more distinguished group of scientists, thus his work was finally recognized. Avogadro’s work helped other scientists to solve more problems and develop more theories. The number 6.02214199 x 1023 is called Avogadro’s number NA, in honor of Aamadeo Avogadro, who was the first person to argue in favor of the existence of atoms.
In fact Avogadro has based his work on the findings of Joseph Gay-Lussac in 1809. Gay-Lussac had discovered that all the gases when subjected to an equal rise in temperature expand by the same amount. Avogadro therefore derived his hypothesis. He also made it clear that the gas particles need not be individual atoms but had made a distinction between the atoms of a substance and its molecules. Avogadro began his career in 1796 by obtaining a doctorate in law and practicing as a lawyer for three years after. In 1800, he began to take private lessons in mathematics and physics and decided to make the natural sciences his profession. He was appointed as a demonstrator at the Academy of Turin in 1806 and the Professor of Natural Philosophy at the College of Vercelli in 1809, and in 1820, he was appointed the professor of mathematical physics.
Avogadro proposed his hypothesis in 1811. At that time there was no data at all on the number of particles in a mole, or an agreement on any atomic weights or the standard. The first measurements which could give an approximate value for Avogadro’s number were observations of Brownian motion by Robert Brown in 1827. Cannizzaro (1860) used the Avogadro’s hypothesis to develop a defensible set of atomic weights based on 1/16 of the atomic weight of oxygen. This was the basis for progressively more accurate estimates for Avogadro’s number over the next 100 years. Reasonable values were available in the late 1800’s from sedimentation equilibria of colloidal particles. Millikan’s oil drop experiment in the early 1900’s gave improved accuracy and was cited in most chemistry text books. Text books in 1958 gave Avogadro’s number as 6.02 times 10 to the 23rd. The current value is 6.022137 times 10 to the 23rd. It is difficult to imagine such a large number as Avogadro’s number. Some idea of its magnitude is given by the following calculation. Let us suppose that a large place with an area of 262,000 square miles, were covered with a layer of fine sand 50 feet thick, each grain of sand being 1/100 of an inch in diameter. There would then be Avogadro’s number of sand particles in this immense sand pile. Avogadro’s number is commonly used to compute the results of chemical reactions. It allows chemists to determine the exact amounts of substances produced in a given reaction. This is called stoichiometry. This large number is approximately equal to the number of protons in a gram of pure protons. It is customary to introduce the term ‘gram molecule’ into explanations of the importance of this number.