Name: chemical formula mass and percent composition
Uploaded: 2020-09-03T13:38:26.000Z
Duration: 2 min 56 s
Channel: JoVE

K12 Standards

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NC K-12 Science Standard Course of Study

9-12

Chemistry

Matter and its Interactions

PS.Chm.3.3

formula-mass-and-mole-concepts-of-compounds

Formula Mass and Mole Concepts of Compounds

Die kleinste repräsentative Einheit einer Verbindung ist das Molekül die durch eine chemische Formel dargestellt wird. Die Atommassen aller Atome in der chemischen Formel ergeben, wenn sie addiert werden, die Molekülmasse der Verbindung, gemessen in Atommasseneinheit. Um zum Beispiel die Molekülmasse von Saccharose oder Tafelzucker zu ermitteln, wird die Atommasse jedes Elements mit der Anzahl der Atome des entsprechenden Elements multipliziert.Die Gesamtsumme ergibt die Molekularmasse von Saccharose. Die Masse aller Moleküle die in einem Mol einer chemischen Verbindung vorhanden sind, wird als Molmasse bezeichnet, gemessen in Gramm pro Mol. Die Molmasse einer Verbindung ist numerisch gleich ihrer Molekülmasse Zum Beispiel hat Saccharose mit einer Molekularmasse von 342, 3 Atommasseneinheiten eine Molmasse von 342, 3 Gramm pro Mol.Die Kenntnis der tatsächlichen Anzahl der in einer chemischen Substanz vorhandenen Moleküle oder Teilchen ist grundlegend für das Verständnis ihrer Zusammensetzung, Wechselwirkungen und Kombinationen. In einer bestimmten Probe einer Verbindung ist das Zählen der tatsächlichen Anzahl von Molekülen mit herkömmlichen Mitteln jedoch unpraktisch. Anhand der Beziehung zwischen Molmasse, Mol und Avogadro-Zahl kann die Gesamtzahl der vorhandenen Moleküle berechnet werden.Dem Konzept zufolge ist die Molmasse einer Verbindung äquivalent zu einem Mol der Verbindung, die aus 6.022 x 10^23 Teilchen besteht. Daher enthalten 342, 3 Gramm Saccharose 6, 022 x 10^23 Saccharosemoleküle. Wenn eine Saccharoseprobe jedoch beispielsweise 150 Gramm wiegt, kann die Anzahl der Moleküle durch Berechnung mit Kreuzmultiplikation bestimmt werden.Das Ergebnis zeigt, dass 150 Gramm Saccharose 2, 63 x 10^23 Saccharosemoleküle ausmachen. Der prozentuale Anteil jedes Elements in einer Verbindung kann durch einen Massenprozentwert ausgedrückt werden. Zur Berechnung wird die Masse des Elements in einem Mol der Verbindung durch die Gesamtmasse von einem Mol der Verbindung geteilt und in einen Prozentsatz umgerechnet.In der Praxis wird zur Berechnung des prozentualen Massenanteils von Wasserstoff in Saccharose die Gesamtmasse der Wasserstoffatome und die Gesamtmasse der Saccharosemoleküle in die Formel einbezogen. Der berechnete Wert zeigt, dass Saccharose 6, 4 Massenprozent Wasserstoff enthält.

formelmasse- und mole-konzepte von verbindungen

<h4>Formelmasse kovalenter Verbindungen</h4> Chemische Formeln stellen die elementare Zusammensetzung von Stoffen dar. Bei kovalenten Verbindungen stellt die Formel die Anzahl und Art der Atome dar, aus denen ein einzelnes Molekül der Substanz besteht; Daher kann die Formelmasse korrekterweise als Molekülmasse bezeichnet werden. Die Summenformel von Chloroform (CHCl3), einer kovalenten Verbindung, gibt an, dass ein einzelnes Molekül ein Kohlenstoffatom, ein Wasserstoffatom und drei Chloratome enthält. Die durchschnittliche Molekülmasse eines Chloroformmoleküls ist gleich der Summe der durchschnittlichen Atommassen dieser Atome: <img alt="Eq1" src="https://www.jove.com/files/core/CDNSource/lessons/1017/1017_Equations-01.png" style="height: 40px;"> <h4>Formelmasse ionischer Verbindungen</h4> Ionische Verbindungen bestehen aus diskreten Kationen und Anionen, die in Verhältnissen kombiniert werden, um elektrisch neutrale Massenmaterie zu ergeben. Die Formelmasse für eine ionische Verbindung wird auf die gleiche Weise berechnet wie die Formelmasse für kovalente Verbindungen: durch Summieren der durchschnittlichen Atommassen aller Atome in der Formel der Verbindung. Die Formel für eine ionische Verbindung stellt jedoch nicht die Zusammensetzung eines einzelnen Moleküls dar, sodass sie möglicherweise nicht korrekt als „Molekularmasse“ bezeichnet wird. Beispielsweise ist gewöhnliches Speisesalz oder Natriumchlorid (NaCl) eine ionische Verbindung, die aus Natriumkationen (Na+) und Chloridanionen (Cl−) besteht, die im Verhältnis 1:1 kombiniert sind. Die Formelmasse für diese Verbindung wird durch Addition der durchschnittlichen Atommassen ihrer Bestandteile berechnet: <img alt="Eq2" src="https://www.jove.com/files/core/CDNSource/lessons/1017/1017_Equations-02.png" style="height: 40px;"> Bei der Berechnung der Formelmasse einer ionischen Verbindung wurden die durchschnittlichen Massen der neutralen Natrium- und Chloratome und nicht die Massen der Natriumkationen und Chloridanionen verwendet. Obwohl ein Natriumkation eine etwas geringere Masse als ein Natriumatom hat (da ihm ein Elektron fehlt), wird dieser Unterschied durch die Tatsache ausgeglichen, dass ein Chloridanion etwas massereicher ist als ein Chloratom (aufgrund des zusätzlichen Elektrons). Darüber hinaus ist die Masse eines Elektrons im Vergleich zur Masse eines typischen Atoms vernachlässigbar klein. <h4>Zusammensetzung in Massenprozent</h4> Die elementare Zusammensetzung einer Verbindung definiert ihre chemische Identität, und chemische Formeln sind die prägnanteste Möglichkeit, diese elementare Zusammensetzung darzustellen. Der Massenprozentsatz jedes Elements in der Verbindung wird als Massenprozent dieses bestimmten Elements bezeichnet. Die prozentuale Zusammensetzung kann berechnet werden, indem die Masse jedes Elements durch die Gesamtmasse der Verbindung dividiert und dann in einen Prozentsatz umgewandelt wird. Die prozentuale Zusammensetzung ist nützlich, um die relative Häufigkeit eines bestimmten Elements in verschiedenen Verbindungen bekannter Formeln zu bewerten. Solange die Molekül- oder Summenformel der betreffenden Verbindung bekannt ist, kann die prozentuale Zusammensetzung aus den Atom- oder Molmassen der Elemente der Verbindung abgeleitet werden. Beispielsweise enthält ein Molekül Salpetersäure (HNO3) ein Stickstoffatom mit einem Gewicht von 14,01 amu, ein Wasserstoffatom mit einem Gewicht von 1,008 amu und drei Sauerstoffatome mit einem Gewicht von (3 × 16,00 amu) = 48,00 amu. Die Formelmasse von Salpetersäure lautet daher (14,01 amu + 1,008 amu + 48,00 amu) = 63,02 amu, und ihre prozentuale Zusammensetzung ist: <img alt="Eq3" src="https://www.jove.com/files/core/CDNSource/lessons/1017/1017_Equations-03.png" style="height: 40px;"> <img alt="Eq4" src="https://www.jove.com/files/core/CDNSource/lessons/1017/1017_Equations-04.png" style="height: 40px;"> <img alt="Eq5" src="https://www.jove.com/files/core/CDNSource/lessons/1017/1017_Equations-05.png" style="height: 40px;"> Dieser Text wurde angepasst von <a href="https://openstax.org/books/chemistry-2e/pages/3-1-formula-mass-and-the-mole-concept">Openstax, Chemistry 2e, Section 3.1: Formula Mass and the Mole Concept</a> und <a href="https://openstax.org/books/chemistry-2e/pages/3-2-determining-empirical-and-molecular-formulas">Openstax, Chemistry 2e, Section 3.2: Determining Empirical and Molecular Formulas.</a>

Formelmasse- und Mole-Konzepte von Verbindungen

Formelmasse kovalenter Verbindungen

Chemische Formeln stellen die elementare Zusammensetzung von Substanzen dar. Für kovalente Verbindungen stellt die Formel die ...

Education

Lehre

JoVE Core

Chemie

Eins

Molecules, Compounds, and Chemical Equations

Moleküle, Verbindungen und chemische Gleichungen

molecules-compounds-and-chemical-equations

KEY TERMS AND CONCEPTS

KERNBEGRIFFE UND KONZEPTE

chemical formula mass and percent composition

Chemical formula mass and percent composition help describe the makeup of compounds. A chemical formula shows which atoms are present and how many of each atom appear in a substance.

For covalent compounds, the formula shows the atoms in one molecule. That is why formula mass can also be called molecular mass. Chloroform, CHCl3, is one example. Its formula shows one carbon atom, one hydrogen atom, and three chlorine atoms. The molecular mass is the sum of their average atomic masses.

Ionic compounds are different because they contain cations and anions that combine in ratios that make the bulk material electrically neutral. Their formula mass is found the same way, by adding the average atomic masses of the atoms in the formula. Sodium chloride, or table salt, is one example. Its formula, NaCl, shows sodium and chloride in a 1:1 ratio. For ionic compounds, the term molecular mass is not the best choice because the formula does not describe a single molecule.

When calculating formula mass for an ionic compound, neutral atom masses are used instead of ion masses. A sodium cation has slightly less mass than a sodium atom because it has lost an electron. A chloride anion has slightly more mass than a chlorine atom because it has gained an electron. The difference is small, and the mass of an electron is negligibly small compared with the mass of a typical atom.

Percent composition tells how much of a compound’s mass comes from each element. It is found by dividing the mass of each element by the total mass of the compound and converting the result to a percentage. This is useful for comparing the relative amount of an element in compounds with known formulas.

Nitric acid, HNO3, shows how the calculation works. One molecule contains one nitrogen atom with a mass of 14.01 amu, one hydrogen atom with a mass of 1.008 amu, and three oxygen atoms with a total mass of 48.00 amu. Its formula mass is 63.02 amu. From that total, the percent composition of each element can be determined.

Chemical Formula Mass and Percent Composition

chemical-formula-mass-and-percent-composition

molecules and compounds

Atomic Elements, Molecules, and Bonds

Matter is made of elements, and elements are built from atoms. An atom is the smallest unit of an element that still keeps that element’s properties. A silver coin, for example, is made of silver atoms. Each atom keeps the unique properties of silver. Elements are pure substances made of identical atoms. They cannot be broken down into simpler substances by chemical changes. Most elements are atomic elements, which use single atoms as their basic unit. Carbon and sodium are examples of atomic...

molecular models

Molecular Model Types in Chemistry

Molecular models help chemists and students visualize the structures and shapes of atoms and molecules. They represent the molecular architecture of chemical compounds in a way that is easier to study than formulas alone. Skeletal models are simple two-dimensional drawings of compounds. They show the molecular framework, or the bonds, without drawing every atom. In this model, many carbon and hydrogen atoms are not shown directly. Their positions are implied by the ends and junctions of the...

organic compounds

Organic Molecules in Everyday Chemistry

Organic molecules are carbon-based compounds found in living things and in many everyday products. Most organic compounds have carbon as the main element, bonded to hydrogen and other carbon atoms. Some carbon-containing substances, such as carbonates, cyanides, and simple oxides like CO and CO2, are not classified as organic. Carbon can form up to four strong bonds, which helps explain why organic compounds can make chains and rings of many sizes and shapes. These molecules appear in...

formula mass and mole concepts of compounds

Chemical formula mass and percent composition help describe the makeup of compounds. A chemical formula shows which atoms are present and how many of each atom appear in a substance. For covalent compounds, the formula shows the atoms in one molecule. That is why formula mass can also be called molecular mass. Chloroform, CHCl3, is one example. Its formula shows one carbon atom, one hydrogen atom, and three chlorine atoms. The molecular mass is the sum of their average atomic masses. Ionic...

experimental determination of chemical formula

experimental-determination-of-chemical-formula

Finding Empirical and Molecular Formulas

Chemical formulas show the elemental makeup of a compound. When a formula is unknown, scientists often start by measuring the masses of the elements in the sample. Those mass data are then used to find the simplest whole-number ratio of atoms, which gives the empirical formula. To get from mass to atom ratio, the masses of the elements are first converted to moles using molar masses. Chemical formulas describe numbers of atoms, not masses, so this step is necessary. In one example, 1.71 grams...

chemical equations

Reading Chemical Equations and Balancing Them

Chemical equations show the identities and relative amounts of substances in a chemical reaction. The substances that react are called reactants, and their formulas are written on the left side of the equation. The substances formed are called products, and their formulas are written on the right side. A plus sign (+) separates formulas on the same side, and an arrow (→) shows the change from reactants to products. The numbers in a chemical equation are shown with coefficients. A coefficient...

key terms and concepts

Learn how to calculate formula mass for covalent and ionic compounds, then use it to find percent composition with examples like chloroform, salt, and nitric acid.

Chemical Formula Mass and Percent Composition | JoVE K12

chemistry

JoVE Core Chemie erweckt allgemeine Konzepte der Chemie durch kompakte und leicht verständliche animierte Videolektionen zum Leben. Außerdem zeigen wir in den Videos Wissenschaftler in Aktion bei klassischen und neuartigen Forschungsexperimenten, wie sie heutzutage in Laboren weltweit durchgeführt wurden.

PS.Chm.4.3

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Ohio’s Learning Standards and Model Curriculum

Structure And Properties Of Matter

Quantifying matter

Interactions Of Matter

Stoichiometry

Tennessee Academic Standards

High School

Matter and Its Interactions

CHEM1.PS1.1

CHEM1.PS1.3

Virginia  Standards of Learning

HIgh School

CH.3

CH.3.a

CH.4

CH.4.a

Arizona Science Standards

Physical Science

HS+C.P1

HS+C.P1U1.7

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New Jersey Student Learning Standards for Science

HS-PS1-7

Texas Essential Knowledge and Skills

CHEM.7

CHEM.7.B

CHEM.8

CHEM.8.A

CHEM.8.B

CHEM.9

CHEM.9.A

Alabama Course of Study Science

9-12.C.1.4.a

Florida Department of Education

SC.912.P.8

SC.912.P.8.7

SC.912.P.8.9

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New York State Science Learning Standards

HS. Chemical Reactions

HS-PS1-7.

Georgia Standards of Excellence

SC3.

The Mole Concept and Avogadro’s Number

Scientific Laws and Theories

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PS.Chm.1.3

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PS.Chm.2.1

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PS.Chm.2.2

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PS.Chm.3.1

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PS.Chm.3.2

Analyze the structure of atoms and isotopes.

Chemical Formula Mass and Percent Composition

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