![]() ![]() Unauthorized duplication or posting on other web sites is expressly prohibited. This page is copyright 2000-2023 by ILPI. ![]() See also: Chemical formula, IUPAC, mass units, molarity.Īdditional definitions from Google and OneLook.Įntry last updated: Tuesday, January 3, 2023. Science geeks get a kick out calling October 23rd (10/23) "mole day" visit the National Mole Day Foundation, Inc.WolframAlpha is a computational search engine that can return all kinds of chemical data, including mole calculations for various materials.The Mole Concept at General Chemistry Online reviews how the mole is used in fundamental chemistry.What Is a Mole? at DigitalFire Corporation.The Concept of Mole and the Avogadro Constant at Chemistry LibreTexts.Formula Mass And The Mole Concept at the open-source textbook, Chemistry, courtesy of Rice University's OpenStax.Laboratory operations are a breeze with Ohaus analytical balances from Safety Emporium. Physical property information such as molecular and formula weights is not required on Safety Data Sheets (and is not always applicable), but if this information is on there it will be found in Section 9 (physical and chemical properties) of the SDS. The formula and molecular weights are also included on Safety Data Sheets in case one needs to calculate a molarity, for example. Moles are used to calculate molarity, a unit of concentration most often used for liquid solutions. Likewise, one mole of water (FW = 18 amu) has a molar mass of 18 grams. In the example we've been using, this tells us that because the FW of benzene is 78 amu, then one mole of benzene must weigh 78 grams. Molar masses (in grams) are therefore numerically equal to formula weights (in amu). The molar mass is the mass in grams of 1 mole of the substance.The abbreviation commonly used for molecular weight is MW. Therefore, as the chemical and molecular formulas of benzene are both C 6H 6, the molecular weight of benzene is also 78 amu. When the chemical formula equals the molecular formula (see same link), then the formula weight is also called the molecular weight.Formula weight is commonly abbreviated FW. Therefore, the formula weight of benzene (C 6H 6) is equal to the mass of six carbon atoms (6 * 12 amu = 72 amu) plus the mass of six hydrogen atoms (6 * 1 amu = 6 amu) = 78 amu. The formula weight of a substance is the sum of the atomic weights of each atom in the chemical formula.You can look these values up in any chemistry textbook or on the web at WebElements. Therefore, the atomic weight of a 12C atom is 12 amu. Just as Avogadro's number is very large, an amu is very small. The IUPAC definition of atomic mass unit (amu) sets the mass of one 12C atom equal to 12 amu.How were we able to tell you that? Using these terms and definitions: So while a mole of 12C (carbon) atoms will weigh 12 grams, a mole of 197Au (gold) atoms will weigh 197 grams and a mole of sodium chloride (NaCl, table salt) will weigh 58.45 grams. So a mole of water (H 2O) has 6.022 x 10 23 water molecules, a mole of carbon atoms has 6.022 x 10 23 carbon atoms and a mole of automobiles (rather unlikely) would have 6.022 x 10 23 automobiles.Ĭlearly, if the objects we are talking about have different masses (weight), then a mole of one substance will also have a different mass than the other. The uncertainty is rounded up to one (two) significant digit(s), and the formula or molar mass is rounded to the same absolute accuracy as the rounded uncertainty.Get your hazardous waste labels from Safety Emporium.Ī mole of anything has Avogadro's number of objects in it. The third rule is to use all digits in the recommended atomic weights and to calculate the absolute maximum uncertainty of the result from the recommended uncertainties of the atomic weights. The second rule is to use all digits in the recommended atomic weights and to estimate the accuracy of the result from the number of decimal places or significant digits in these. This rule is appropriate for beginners but has some disadvantages. The first rule is to use four digits in atomic weights and consider the calculated formula or molar mass as given with four significant digits. Elementary propagation of error theory is applied and the accuracy of recommended atomic weights as well as the accuracy of elementary laboratory work is considered. This article addresses the question often asked by students, “How many digits should I use when calculating the formula or molar mass of a substance?†Three rules of increasing complexity are proposed and discussed. ![]()
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