Name: mole, mass, and avogadro’s number
Uploaded: 2020-09-03T13:38:25.000Z
Duration: 1 min 54 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.2.1

Molar Mass

La tabla periódica ofrece la masa atómica promedio de cada átomo. No obstante, las muestras macroscópicas contienen un número demasiado grande de átomos. Por lo tanto, es fundamental utilizar una unidad de conteo denominada número de Avogadro.El valor del número de Avogadro, que se representa con el símbolo NA, por lo general, es de 6, 022 X 10^23. Su valor es igual al número de átomos en 12 gramos exactos del isótopo puro de carbono-12. El término mole, abreviado mol"se usa para describir el número de Avogadro, así como el término tradicional docena"se usa para describir una cantidad de 12 objetos.Sin embargo, una docena de objetos distintos puede tener un peso diferente a pesar de poseer el mismo número de objetos. De forma similar, los moles de distintos elementos tienen masas diferentes, pero siempre contienen el mismo número de átomos. A la masa en gramos de 1 mol de un elemento se le conoce como masa molar y se expresa en gramos por mol.Su valor numérico coincide con el de la masa atómica del elemento. Por tanto, la definición del mol nos permite contar partículas pesándolas. La masa molar y el número de Avogadro se pueden usar como factores de conversión.Esto se puede usar para calcular el número de átomos en una barra de 5 gramos de oro. La masa molar promedio del oro es 196, 96 gramos por mol. Entonces, para convertir la masa a moles, se divide la masa de la barra entre la masa molar promedio.Luego, se multiplica el número de moles por el número de Avogadro para obtener el número total de átomos en la muestra. Entonces, esta barra de oro contiene 1529 X 10^22 átomos.

masa molar

La identidad de una sustancia se define no sólo por los tipos de átomos o iones que contiene, sino por la cantidad de cada tipo de átomo o ión. Por ejemplo, el agua, H2O, y el peróxido de hidrógeno, H2O2, se parecen en que sus respectivas moléculas están compuestas de átomos de hidrógeno y oxígeno. Sin embargo, debido a que una molécula de peróxido de hidrógeno contiene dos átomos de oxígeno, a diferencia de la molécula de agua, que sólo tiene uno, las dos sustancias presentan propiedades muy diferentes.
 
 Los átomos y las moléculas son extremadamente pequeños. Por lo tanto, para medir sus cantidades macroscópicas, se necesita una unidad científica estándar. El mol es una unidad de cantidad similar a las unidades familiares como par, docena, bruto, etc. Proporciona una medida específica del número de átomos o moléculas en una muestra de materia. La connotación latina para la palabra “mol” es “gran masa” o “a granel”, que es consistente con su uso como nombre para esta unidad. El mol proporciona un enlace entre una propiedad macroscópica fácilmente medida, masa a granel, y una propiedad fundamental extremadamente importante, número de átomos, moléculas, etc.
 
 Un mol de una sustancia es la cantidad en la que hay 6,02214076 × 1023 entidades discretas (átomos o moléculas). Este gran número, convenientemente redondeado a 6,022 ×  1023, es una constante fundamental conocida como el número de Avogadro (NA) o la constante de Avogadro en honor del científico italiano Amedeo Avogadro. Esta constante se reporta correctamente con una unidad explícita de “por mol”.
 
 Consistente con su definición como unidad de cantidad, 1 mol de cualquier elemento contiene el mismo número de átomos que 1 mol de cualquier otro elemento. Sin embargo, las masas de 1 mol de diferentes elementos son diferentes, ya que las masas de los átomos individuales son drásticamente diferentes. La masa molar de un elemento (o compuesto) es la masa en gramos de 1 mol de esa sustancia, una propiedad expresada en unidades de gramos por mol (g/mol).
 
 La masa molar de cualquier sustancia es numéricamente equivalente a su peso o fórmula atómica en uma. Según la definición de uma, un solo átomo de carbono pesa 12 uma (su masa atómica es de 12 uma). Un mol de carbono pesa 12 g (12 g C = 1 mol de átomos de C = 6,022 × 1023 átomos de C), y la masa molar de carbono es 12 g/mol. Esta relación se mantiene para todos los elementos ya que sus masas atómicas se miden en relación con la de la sustancia de referencia uma, el carbono-12. Al extender este principio, la masa molar de un compuesto en gramos es numéricamente equivalente a su masa de fórmula en uma. Por ejemplo, el helio tiene una masa atómica de 4,002 uma y una masa molar de 4,002 g/mol.
 
 Si bien la masa atómica y la masa molar son numéricamente equivalentes, tenga en cuenta que son muy diferentes en términos de escala. Para apreciar la enormidad del mol, considere una pequeña gota de agua que pesa aproximadamente 0,03 g. Aunque esto representa sólo una pequeña fracción de 1 mol de agua (~18 g), contiene más moléculas de agua de lo que se puede imaginar. Si las moléculas se distribuyeran equitativamente entre los aproximadamente siete mil millones de personas en la tierra, cada persona recibiría más de 100 mil millones de moléculas de agua.
 
 El mol define la relación entre la masa y el número de átomos. Esto permite calcular el número de átomos utilizando formas adecuadas del factor de conversión: 1 mol de átomos = 6,022 × 1023 átomos. Para convertir entre la masa de un elemento (en gramos) y el número de moles, se utiliza como factor de conversión la masa molar del elemento (g/mol).
 
 Texto 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 de fórmula y el concepto de mol.</a>

Masa Molar

La identidad de una sustancia se define no solo por los tipos de átomos o iones que contiene, sino por la cantidad de cada tipo de átomo o ion. Por ejemplo...

Education

Educación

JoVE Core

Química

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KEY TERMS AND CONCEPTS

TÉRMINOS Y CONCEPTOS CLAVE

mole, mass, and avogadro’s number

The mole links mass and the number of particles in a substance. It gives chemists a standard way to count atoms and molecules in samples that are far too small to see. It also helps show why substances with the same kinds of atoms can still have very different properties, like water, H2O, and hydrogen peroxide, H2O2.

The mole is an amount unit, like a pair or a dozen. One mole contains 6.02214076 × 10^23 discrete entities, such as atoms or molecules. This number is usually rounded to 6.022 × 10^23 and is called Avogadro’s number, or the Avogadro constant, named for Amedeo Avogadro. The constant is written with the unit per mole.

One mole of any element contains the same number of atoms as one mole of any other element. The masses are different, though, because atoms have different individual masses. That is why one mole of one element does not weigh the same as one mole of another element.

Molar mass is the mass in grams of one mole of a substance. It is reported in grams per mole, or g/mol. The molar mass of an element or compound is numerically equal to its atomic mass or formula mass in amu. For example, carbon has an atomic mass of 12 amu, so 1 mole of carbon has a mass of 12 g and a molar mass of 12 g/mol.

This same relationship works for other elements and for compounds. Helium, for example, has an atomic mass of 4.002 amu and a molar mass of 4.002 g/mol. Although the numbers match, atomic mass and molar mass are very different in scale.

A tiny drop of water can still contain an enormous number of molecules. A drop that weighs about 0.03 g is only a small part of 1 mole of water, which is about 18 g. Even so, it holds more water molecules than can easily be imagined. If those molecules were shared equally among the roughly seven billion people on Earth, each person would still get more than 100 billion molecules of water.

The mole also lets scientists convert between mass and amount. Using the relationship 1 mole of atoms = 6.022 × 10^23 atoms, the number of atoms can be calculated from a sample. The molar mass of an element is also used as a conversion factor to move between grams and moles.

Mole, Mass, and Avogadro’s Number

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molar mass

The mole links mass and the number of particles in a substance. It gives chemists a standard way to count atoms and molecules in samples that are far too small to see. It also helps show why substances with the same kinds of atoms can still have very different properties, like water, H2O, and hydrogen peroxide, H2O2. The mole is an amount unit, like a pair or a dozen. One mole contains 6.02214076 × 10^23 discrete entities, such as atoms or molecules. This number is usually rounded to 6.022 ×...

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Learn how the mole connects mass, atoms, and molecules through Avogadro’s number and molar mass, with clear examples for high school chemistry.

Mole, Mass, and Avogadro’s Number | JoVE K12

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Stoichiometry

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CH.2

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CH.4

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Florida Department of Education

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Mole, Mass, and Avogadro’s Number

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