Amount of Substance
Amount of substance refers to the quantity of a particular substance, measured in moles. It is a fundamental concept in chemistry and is used to quantify the number of atoms, molecules, or ions in a sample. The amount of substance is crucial for understanding chemical reactions and stoichiometry.
6 Key excerpts on "Amount of Substance"
eBook - ePub- Jeffrey Gaffney, Nancy Marley(Authors)
- 2017(Publication Date)
- Elsevier(Publisher)
...Although the common use of the term “Amount of Substance” used in Engineering may be interpreted as the weight (in grams) or the volume (in cm 3) of a substance, in chemistry the amount of a substance is a measure of the number of fundamental particles, such as atoms, molecules, or ions that are present in a given mass of substance. The SI base unit for the amount of a substance is the mole. The exact definition of a mole is the mass of any substance, which contains the same number of fundamental units as there are atoms in exactly 12.000 g of 12 C. Carbon-12 was chosen to serve as the reference standard of the mole unit for the International System of Units since it was also chosen to serve as the reference standard for atomic mass and the atomic mass unit, as described in Chapter 1. The fundamental units of a substance may be atoms, molecules, ions, or chemical formula units, depending on the type of substance. The number of atoms in 12.000 g of 12 C has been determined to be equal to 6.022 × 10 23. So, one mole of any element always contains 6.022 × 10 23 atoms, one mole of any covalent compound always contains 6.022 × 10 23 molecules, and one mole of any ionic compound always contains 6.022 × 10 23 chemical formula units. The number 6.022 × 10 23 by itself is known as Avogadro's number (N A), after the nineteenth century scientist Amedeo Avogadro. It is actually a conversion factor between the number of moles and the number of fundamental units in a substance. N A = 6.022 × 10 23 mol or 6.022 × 10 23 mol − 1 (1) The importance of the mole concept to chemistry is that it can be extended to the molecular level. If one mole of oxygen reacts with two moles of hydrogen to form two moles of water, O 2 + H 2 → 2H 2 O then one atom of oxygen reacts with two atoms of hydrogen to form one molecule of water. O + 2H → H 2 O The mass of one mole of a substance is called the molar mass of that substance...
eBook - ePubFoundations for Teaching Chemistry
Chemical Knowledge for Teaching
- Keith S. Taber(Author)
- 2019(Publication Date)
- Routledge(Publisher)
...7 The most fundamental chemical concept: Substance As suggested in Chapter 6, a canonical understanding of chemistry depends upon appreciating what chemists mean by something being a substance. The ‘substance’ concept is a prerequisite for understanding other core chemical concepts such as ‘element’ and ‘compound’ (see Chapter 8) and ‘chemical reaction’ (see Chapter 11). The notion of a substance One of the most basic concepts in chemistry is that of substance. Chemistry is fundamentally the science that studies the properties of substances, including (indeed, especially) how they interact. Before we can do chemistry, we need a notion of what we mean by ‘substance’. In everyday use, substance may refer to anything substantial (as opposed to something ephemeral or imaginary): the earth, the table, an apple. So, any ‘stuff’ may be considered to have substance. Matter, materials, and substances In chemistry, however, we distinguish matter (‘stuff’ generally) from substances that are considered to be particular kinds of stuff. Some familiar materials are effectively single substances: diamonds, table salt, baking soda, aluminium foil. But most materials met outside of the chemistry laboratory are not single substances in this way. Air is not a substance, nor is sea water (if tap water in some parts of the world comes pretty close). The soil is certainly not a ‘pure’ substance. Organic materials – hair, bone, wood – are complex materials and not substances. Some metal objects we come across in everyday use are close to being composed of a pure substance, but most are alloys which are mixtures. Very few metals (examples would be gold, silver, sometimes copper) are found native, and the minerals that are the sources of ores are often not single substances either. By contrast, a well-stocked chemical cupboard may contain a wide range of pure substances, and it is these that are the usual focus of laboratory work in school chemistry...
eBook - ePub- Atef Korchef(Author)
- 2022(Publication Date)
- CRC Press(Publisher)
...percent refers to the ratio of the mass of one element to the total mass of a compound. The mass percent of an element, % (element), is determined bythe following equation: % e l e m e n t = n × a t o m i c m a s s o f t h e e l e m e n t m o l e c u l a r m a s s o f t h e c o m p o u n d × 100 where n is the number of atoms of the element in the compound. A balanced chemical equation is an equation that represents the correct amounts of reactants and products in a chemical reaction. The number of atoms of each element is the same on both sides of the equation. To balance achemical equation, start by balancing those elements that appear in only one reactant and one product. Example of a balanced chemical equation: 2 HgO → 2 Hg + 1/2 O 2 Stoichiometry is the study of mass relationships that exist between reactants (substances consumed) and products (substances produced) in a chemical reaction. Use coefficients in the balanced equation to determine the relationships between the number of moles of reactants andproducts. Then, calculate the number of moles and the mass of the desired quantity. A solution consists of a smaller amount of a substance, the solute, dissolved in a larger amount of another substance, the solvent. The concentration of the solution is expressed as the amount of solute dissolved in a given amount of solution. The term most used is Molarity (M), defined as number of moles of solute per liter of solution (M = n/V). A common unit of molarity is M(= mol L −1). The molality is defined as the number of moles of the solute per kilogram of the solvent. The SI unit of molality is mol kg −1. The solubility designates the maximum mass concentration of the solute in the solvent, at a given temperature. The solution thus obtained is saturated...
eBook - ePub- Kevin R. Reel(Author)
- 2013(Publication Date)
- Research & Education Association(Publisher)
...This value can be used to determine the number of particles in a mole of atoms or molecules. Example: How many atoms are in 0.2 moles of atoms? Solution: MASS • Atomic and molecular weights can be used to convert moles to grams, and vice versa. Example: What is the mass of 4.20 moles of carbon atoms? Solution: GASES • While stoichiometry problems can result in answers in moles, the ideal gas law can be used to convert that number of moles to some unknown variable in the ideal gas law equation. • At STP (standard temperature and pressure), 1.0 mole of gas occupies 22.4 liters. This can be used as a conversion factor in solving stoichiometric equations. Example: What is the volume of 8.26 moles of gas at STP? Solution: SOLUTIONS • Stoichiometric problems that involve solutions usually require a molar solution conversion at some point to get the answer, where Example: How many moles of glucose exist in 1.4 liters of a 0.20-molar solution of glucose? Solution: STOICHIOMETRY PROBLEMS • Stoichiometry problems refer to a type of question in which the student is given an amount of reactant or product in a chemical reaction, and then asked to find the corresponding amount of reactant or product. • Stoichiometry problems can all be solved using the following steps: 1. Balance the reaction. 2. Write down the units of the answer next to an equals sign “=”. 3. On the other side of an equals sign, write down the number and units of the given information. 4. Use a ratio to convert the given information into moles. 5. For the next ratio, use the balanced reaction to relate the number of moles of the given substance to the number of moles of the substance in the answer. 6. Convert the number of moles of the substance in the answer to the actual units of the answer...
eBook - ePubUnderstanding Bioanalytical Chemistry
Principles and Applications
- Victor A. Gault, Neville H. McClenaghan(Authors)
- 2013(Publication Date)
- Wiley(Publisher)
...They decided to use Avogadro’s number. What is a mole? A mole is a term that represents a number; just like the word ‘dozen’ represents ‘12’, the word ‘mole’ represents 6.02 × 10 23 (or 602 216 900 000 000 000 000 000). The term mole, while initially confusing, is extremely useful. To give an example: if we were to count the number of water molecules in a single drop it would be around 10 trillion (10 000 000 000 000), so rightly or wrongly chemists argue that it is easier to quantify such numbers in moles and thus cut down on the number of zeros! Why 6.02 × 10 23 ? This number is ‘Avogadro’s number’, named after the Italian physics professor who proposed that equal volumes of different gases at the same temperature contain the same number of molecules. In its simplest form, 1 mol of any substance contains 6.02 × 10 23 atoms or molecules of that substance, and as this relationship was first put forward by Avogadro they named this number after him. Concept of the mole A defined mass of an element (its atomic weight) contains an exact number of atoms, that is, Avogadro’s number. Therefore, for any given molecule, one mole of the substance has a mass (in grams) equal (numerically) to the atomic mass of the molecule. One mole is the number of atoms in exactly 12 thousandths of a kilogram (i.e...
eBook - ePub- Dov M. Gabbay, Paul Thagard, John Woods, Dov M. Gabbay, Paul Thagard, John Woods(Authors)
- 2011(Publication Date)
- North Holland(Publisher)
...Substances The Ontology of Chemistry Jaap van Brakel 1. Terminological Preliminaries This article aims to offer a preliminary introduction to the “rough ground” of the ontology of chemistry. Although chemistry has often been described as the study of the transformation of substances, there is no generally agreed upon definition of (chemical) substance. 1 In this article we will address the variety and classification of a great variety of stuff. No sharp line will be drawn between the physical, chemical, and material sciences. The issue of the nature of the relations between different “levels” (molar, molecular, quantum mechanical, etc.) is not addressed here (see the article on ‘Reduction, Physicalism, and Supervenience’ in Part 5 of this Volume). In this article all such ‘levels’ are assumed to be equally real. 1 The German normalisation institute DIN has declared substance (Stoff) “nicht normfähig” (not capable of being defined). Materials such as paper, gold, steel, glass, or helium are the product of producing and processing practices (making gold, dye-stuffs, superconductors, glassy metals, buckminsterfullerene, etc.). Such processing practices include operations that separate and mix materials as well as operations that aim at chemical transformation. Chemical operations are typically followed by physical and/or mechanical “unit operations” to purify and concentrate (separate, isolate) the product (so called down-stream processing). 2 2 Separation methods form a neglected core of chemistry. The Dutch word for chemistry is “scheikunde” (German: Scheidekunst), literally meaning “knowledge and art of separation,” a method “utterly different from other modes of analysis known in the empirical sciences” [ Klein, 2008,38]...
