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

La unidad representativa más pequeña de un compuesto es la molécula representada por una fórmula química. Las masas atómicas de todos los átomos en la fórmula química, si se agregan, dan la masa molecular del compuesto, medido en unidad de masa atómica. Por ejemplo, para encontrar la masa molecular de la sacarosa o azúcar de mesa, la masa atómica de cada elemento se multiplica por el número de átomos del elemento correspondiente.La suma total da la masa molecular de la sacarosa. La masa de todas las moléculas presentes en un mol de un compuesto químico se llama masa molar, medida en gramos por mol. La masa molar de un compuesto es numéricamente igual a su masa molecular Por ejemplo, la sacarosa, con una masa molecular de 342, 3 unidades de masa atómica, tendrá una masa molar de 342, 3 gramos por mol.Conocer el número real de moléculas o partículas presentes en una sustancia química es fundamental para comprender su composición, interacciones y combinaciones. Sin embargo, en una muestra dada de un compuesto, contar el número real de moléculas por métodos normales no es práctico. Empleando la relación entre la masa molar, el mol y el número de Avogadro, se pueden calcular las moléculas totales presentes.Según este concepto, la masa molar de un compuesto es equivalente a un mol del compuesto, lo que constituye 6.022 x 10^23 partículas. Por lo tanto, 342, 3 gramos de sacarosa contienen 6, 022 x 10^23 moléculas de sacarosa. Sin embargo, si una muestra de sacarosa pesa 150 gramos, por ejemplo, entonces el número de moléculas se puede determinar mediante un cálculo utilizando un método de multiplicación cruzada.El resultado muestra que 150 gramos de sacarosa constituyen 2, 63 x 10^23 moléculas de sacarosa. El porcentaje de cada elemento en un compuesto se puede expresar usando un valor de porcentaje de masa. Para calcular, la masa del elemento en un mol del compuesto se divide por la masa total de un mol del compuesto y se lo convierte a porcentaje.En la práctica, para calcular el porcentaje en masa de hidrógeno en sacarosa, la masa total de átomos de hidrógeno y la masa total de moléculas de sacarosa se incluyen en la fórmula. El valor calculado muestra que la sacarosa contiene 6, 4 por ciento de hidrógeno en masa.

conceptos de masa fórmula y mol de los compuestos

<h4>Masa Fórmula de los Compuestos Covalentes</h4>
 
 Las fórmulas químicas representan la composición elemental de las sustancias. En el caso de los compuestos covalentes, la fórmula representa el número y tipo de átomos que componen una sola molécula de la sustancia; por lo tanto, la masa fórmula puede denominarse correctamente como masa molecular. La fórmula molecular del cloroformo (CHCl3), un compuesto covalente, indica que una sola molécula contiene un átomo de carbono, un átomo de hidrógeno y tres átomos de cloro. La masa molecular promedio de una molécula de cloroformo es igual a la suma de las masas atómicas promedio de estos átomos:
 
 <img alt="Eq1" src="https://www.jovecore.com/CDNSource/lessons/1017/1017_Equations-01.png" style="height: 40px;" />
 
 <h4>Masa Fórmula de los Compuestos Iónicos</h4>
 
 Los compuestos iónicos se componen de cationes y aniones discretos que se combinan en proporciones para producir materia a granel eléctricamente neutra. La masa fórmula para un compuesto iónico se calcula de la misma manera que la masa fórmula para compuestos covalentes: Sumando las masas atómicas medias de todos los átomos de la fórmula del compuesto. Sin embargo, la fórmula de un compuesto iónico no representa la composición de una molécula discreta, por lo que no puede denominarse correctamente ‘masa molecular’.
 
 Por ejemplo, la sal común de mesa o el cloruro de sodio (NaCl) es un compuesto iónico formado por cationes de sodio (Na+) y aniones de cloruro (Cl−) combinados en una relación de 1:1. La masa fórmula para este compuesto se calcula agregando las masas atómicas medias de sus elementos constituyentes:
 
 <img alt="Eq2" src="https://www.jovecore.com/CDNSource/lessons/1017/1017_Equations-02.png" style="height: 40px;" />
 
 Al calcular la masa fórmula de un compuesto iónico, se utilizaron las masas medias de átomos de sodio y cloro neutros, en lugar de las masas de cationes de sodio y aniones de cloruro. Aunque un catión de sodio tiene una masa ligeramente más pequeña que un átomo de sodio (ya que le falta un electrón), esta diferencia será compensada por el hecho de que un anión de cloruro es ligeramente más grande que un átomo de cloro (debido al electrón extra). Además, la masa de un electrón es insignificante con respecto a la masa de un átomo típico.
 
 <h4>Composición Porcentual de la Masa</h4>
 
 La composición elemental de un compuesto define su identidad química y las fórmulas químicas son la manera más concisa de representar esta composición elemental. El porcentaje de masa de cada elemento del compuesto se denomina porcentaje de masa de ese elemento en particular. La composición porcentual se puede calcular dividiendo la masa de cada elemento entre la masa total del compuesto y, a continuación, convirtiéndola en un porcentaje.
 
 La composición porcentual es útil para evaluar la abundancia relativa de un elemento dado en diferentes compuestos de fórmulas conocidas. Mientras se conozca la fórmula molecular o empírica del compuesto en cuestión, la composición porcentual puede derivarse de las masas atómicas o molares de los elementos del compuesto. 
 
 Por ejemplo, una molécula de ácido nítrico (HNO3) contiene un átomo de nitrógeno que pesa 14,01 uma, un átomo de hidrógeno que pesa 1,008 uma y tres átomos de oxígeno que pesan (3 × 16,00 uma) = 48,00 uma. La masa fórmula del ácido nítrico es por lo tanto (14,01 uma + 1,008 uma + 48,00 uma) = 63,02 uma, y su composición porcentual es:
 
 <img alt="Eq3" src="https://www.jovecore.com/CDNSource/lessons/1017/1017_Equations-03.png" style="height: 40px;" />
 
 <img alt="Eq4" src="https://www.jovecore.com/CDNSource/lessons/1017/1017_Equations-04.png" style="height: 40px;" />
 
 <img alt="Eq5" src="https://www.jovecore.com/CDNSource/lessons/1017/1017_Equations-05.png" style="height: 40px;" />
 
 Este texto ha sido adaptado de <a href="https://openstax.org/books/chemistry-2e/pages/3-1-formula-mass-and-the-mole-concept">Openstax, Química 2e, Sección 3.1: Masa Fórmula y el Concepto Mol</a> y <a href="https://openstax.org/books/chemistry-2e/pages/3-2-determining-empirical-and-molecular-formulas">Openstax, Química 2e, Sección 3.2: Determinación de fórmulas empíricas y moleculares.</a>

Conceptos de Masa Fórmula y Mol de los Compuestos

Masa de la fórmula de compuestos covalentes

Las fórmulas químicas representan la composición elemental de las sustancias. En el caso de los compuestos covalentes, la fórmula representa el ...

Education

Educación

JoVE Core

Química

Molecules, Compounds, and Chemical Equations

Moléculas, compuestos y ecuaciones químicas

molecules-compounds-and-chemical-equations

KEY TERMS AND CONCEPTS

TÉRMINOS Y CONCEPTOS CLAVE

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...

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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...

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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 Química da vida a los conceptos de química general mediante lecciones de vídeo basadas en animaciones, concisas y fáciles de entender. Además, en los vídeos de científicos en acción, se muestran experimentos de investigación clásicos y originales realizados en laboratorios de todo el mundo.

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

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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

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Georgia Standards of Excellence

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The Mole Concept and Avogadro’s Number

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Chemical Formula Mass and Percent Composition

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