Name: matter: elements, compounds, and mixtures
Uploaded: 2020-09-03T13:38:25.000Z
Duration: 3 min 35 s
Channel: JoVE

K12 Standards

north-carolina-k-12-science-standard-course-of-study

North Carolina K-12 Science Standard Course of Study

9-12

Chemistry

Energy

PS.Chm.7.1

Classifying Matter by Composition

La materia è composta da atomi, le più piccole unità di base, e molecole, che si formano combinando insieme due o più atomi. In base alla sua composizione, la materia può essere classificata in due gruppi:sostanze pure e miscele. Per definizione, una materia si definisce pura se è composta da un solo elemento, con una composizione totalmente uniforme.

Per esempio, prendiamo l'idrogeno. L'idrogeno è costituito soltanto da atomi di idrogeno. Allo stesso modo, l'acqua è composta soltanto da molecole d'acqua.

Queste composizioni non variano da campione a campione. Le sostanze pure possono essere classificate in due tipi:elementi e composti, a seconda che possano venire scomposte o meno. Gli elementi sono sostanze pure che non possono essere scomposte in sostanze più semplici usando mezzi chimici.

Per esempio, l'idrogeno è un elemento. I composti, al contrario, sono sostanze che possono essere separate nei loro costituenti tramite metodi chimici. Per esempio l'acqua, anch'essa é una sostanza pura, ma può essere scomposta chimicamente in due sostanze più semplici, idrogeno e ossigeno, il che significa che si tratta di un composto.

Sulla Terra, i composti sono più comuni degli elementi puri, perché la maggior parte degli elementi si combini facilmente con altri elementi. Per esempio, il gesso usato per scrivere sulla lavagna è fatto di calcio, carbonio e ossigeno;lo zucchero è composto da carbonio, idrogeno e ossigeno. A differenza delle sostanze pure, le miscele sono costituite da uno o più componenti.

La loro proporzione può anche variare da campione a campione. Per esempio, la limonata è una miscela di tre componenti:succo di limone, zucchero e acqua, e le loro proporzioni possono essere variate per rendere la bevanda più o meno dolce. Le miscele stesse possono essere classificate in due tipi:omogenee ed eterogenee, a seconda di quanto uniformemente le sostanze si mescolino al loro interno.

Una miscela omogenea mostra una composizione uniforme, e appare visivamente la medesima ovunque. Viene spesso definita come una soluzione. Per esempio, un cucchiaio di sale disciolto in acqua dà una miscela omogenea, poiché ogni goccia di quella miscela ha la stessa composizione.

Allo stesso modo, anche la limonata è una miscela omogenea. In una miscela eterogenea, i componenti non sono distribuiti uniformemente, e quindi la composizione varia da punto a punto. Per esempio la sabbia mescolata alla limatura di ferro:in questo caso, parti diverse di questa miscela avranno probabilmente quantità diverse di limatura di ferro e sabbia.

In ogni modo, qualsiasi miscela, omogenea o eterogenea, può essere separata nei suoi componenti puri attraverso metodi fisici, senza modificare le identità dei componenti. Per esempio, il sale può essere recuperato da una soluzione acquosa riscaldando la miscela fino alla sua secchezza. Allo stesso modo, la limatura di ferro può essere separata dalla sabbia utilizzando un magnete.

classificazione della materia attraverso la composizione

Materia: sostanze pure e miscele

Secondo la sua composizione, la materia può essere classificata in due grandi categorie: sostanze pure e miscele.

Una sostanza pura è una forma di materia che ha una composizione costante con proprietà uniformi. Ad esempio, qualsiasi campione di saccarosio ha la stessa composizione e le stesse proprietà fisiche, come punto di fusione, colore e dolcezza, indipendentemente dalla fonte da cui è isolato.

Una miscela 蠣è composto da due o più tipi di materia che possono essere presenti in quantità variabili e possono essere separati da cambiamenti fisici, come l'evaporazione. I componenti di una miscela mantengono le loro identità distinte.

Sostanze pure: elementi e composti

Le sostanze pure possono essere divise in due classi: elementi e composti. Le sostanze pure che non possono essere scomposte in sostanze più semplici mediante trasformazioni chimiche sono chiamate elementi. Ferro, argento, oro, alluminio, zolfo, ossigeno e rame sono elementi.

Le sostanze pure che possono essere scomposte mediante cambiamenti chimici sono chiamate composti. Questa decomposizione può produrre elementi, altri composti o entrambi. L'ossido di mercurio (II), un solido cristallino arancione, può essere scomposto dal calore negli elementi mercurio e ossigeno. Quando riscaldato in assenza di aria, il composto saccarosio viene scomposto nell'elemento carbonio e nel composto acqua. Il cloruro d'argento (I) è un solido bianco che può essere scomposto nei suoi elementi, argento e cloro, mediante l’assorbimento della luce.

Le proprietà degli elementi combinati sono diverse da quelle nello stato libero o non combinato. Ad esempio, lo zucchero bianco cristallino (saccarosio) è un composto risultante dalla combinazione chimica dell'elemento carbonio, che è un solido nero in una delle sue forme non combinate, e dei due elementi idrogeno e ossigeno, che sono gas incolori quando non combinati. Il sodio libero, un elemento solido metallico morbido e lucido, e il cloro libero, un elemento gassoso giallo-verde, si combinano per formare il cloruro di sodio (sale da cucina), un composto solido bianco cristallino.

Miscele: omogenee ed eterogenee

Una miscela omogeneo, chiamato anche soluzione, presenta una composizione uniforme e appare visivamente la stessa ovunque. Un esempio di soluzione è una bevanda sportiva, composta da acqua, zucchero, coloranti, aromi ed elettroliti mescolati insieme in modo uniforme. Ogni goccia di una bevanda sportiva ha lo stesso sapore perché contiene la stessa quantità di acqua, zucchero e altri componenti. Tieni presente che la composizione di una bevanda sportiva può variare: potrebbe essere preparata con più o meno zucchero, aromi o altri componenti ed essere comunque una bevanda sportiva. Altri esempi di miscele omogenei includono aria, sciroppo d'acero, benzina e una soluzione di sale in acqua.

Una miscela la cui composizione varia da punto a punto è detta miscela eterogenea. Il condimento italiano è un esempio di miscela eterogenea. La sua composizione può variare perché può essere preparata con quantità variabili di olio, aceto ed erbe aromatiche. Non è lo stesso da un punto all'altro in tutta la miscela: una goccia può essere principalmente aceto, mentre un'altra goccia può essere principalmente olio o erbe perché l'olio e l'aceto si separano e le erbe si depositano. Altri esempi di miscele eterogenee sono i biscotti con gocce di cioccolato (possiamo vedere i pezzetti separati di cioccolato, frutta secca e impasto) e il granito (possiamo vedere quarzo, mica, feldspato e altro).

Qualsiasi miscela, omogenea o eterogenea, può essere separata in componenti puri con mezzi fisici senza modificare l'dentità dei componenti. Sebbene esistano poco più di 100 elementi, decine di milioni di composti chimici risultano da diverse combinazioni di questi elementi. Ogni composto ha una composizione specifica e possiede proprietà chimiche e fisiche definite che lo distinguono da tutti gli altri composti. Naturalmente, ci sono innumerevoli modi di combinare elementi e composti per formare miscele diverse.

Questo testo è adattato da <a href="https://openstax.org/books/chemistry-2e/pages/1-2-phases-and-classification-of-matter">Openstax, Chemistry 2e, Section 1.2: Phases and Classification of Matter.</a>

Classificazione della materia attraverso la composizione

Materia: Sostanze pure e miscele
In base alla sua composizione, la materia può essere classificata in due grandi categorie: sostanze pure e ...

Education

Didattica

JoVE Core

Chimica

Introduction: Matter and Measurement

Introduzione: Materia e Misurazione

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

matter: elements, compounds, and mixtures

Matter can be grouped by composition into pure substances and mixtures. A pure substance has a constant composition throughout and uniform properties. For example, any sample of sucrose has the same composition and the same physical properties, such as melting point, color, and sweetness, no matter where it is isolated from.

A mixture contains two or more kinds of matter in varying amounts. Its parts can be separated by physical changes, such as evaporation. The components keep their own identities, so the mixture is not a new substance in the same way a compound is.

Pure substances are divided into elements and compounds. Elements cannot be broken down into simpler substances by chemical changes. Iron, silver, gold, aluminum, sulfur, oxygen, and copper are examples of elements.

Compounds are pure substances that can be broken down by chemical changes. This breakdown may produce elements, other compounds, or both. Mercury(II) oxide can be heated to form mercury and oxygen, sucrose can break down into carbon and water when heated without air, and silver(I) chloride can be broken down by light into silver and chlorine.

The properties of combined elements are different from the properties of the elements in their free state. White crystalline sugar comes from carbon, hydrogen, and oxygen, but those elements look very different when uncombined. Free sodium is a soft, shiny metal, and free chlorine is a yellow-green gas, yet together they form sodium chloride, a white crystalline solid.

Mixtures can be homogeneous or heterogeneous. A homogeneous mixture, also called a solution, has a uniform composition and looks the same throughout. Sports drink is one example. It contains water, sugar, coloring, flavoring, and electrolytes mixed evenly, so each drop tastes the same. Its exact composition can still vary and remain a sports drink. Air, maple syrup, gasoline, and salt water are other homogeneous mixtures.

A heterogeneous mixture has a composition that varies from point to point. Italian dressing is one example, since the amounts of oil, vinegar, and herbs can differ and the parts may separate or settle. Chocolate chip cookies and granite are also heterogeneous mixtures because their different parts can be seen.

Any mixture, whether homogeneous or heterogeneous, can be separated into pure components by physical means without changing what the components are. There are just over 100 elements, but they combine in many ways to form tens of millions of compounds. Each compound has a specific composition and its own chemical and physical properties. Elements, compounds, and mixtures can combine in countless ways to make matter.

Matter: Elements, Compounds, and Mixtures

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Study Of Matter

Classification of matter

Physical Geology

Minerals

Crystallinity (crystal structure)

Virginia  Standards of Learning

HIgh School

CH.7

CH.7.a

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ES.4

ES.4.a

PS.3

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Arizona Science Standards

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Earth and Space Science

HS.E1

HS.E1U1.12

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HS-ESS1-2

Texas Essential Knowledge and Skills

CHEM.2

CHEM.2.A

Alabama Course of Study Science

Matter and Its Interactions

9-12.PS.3.5

9-12.PS.3.5.a

Next Generation Science Standards

HS-PS1-5

HS-PS1-4

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IPC.7

IPC.7.C

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Matter: Elements, Compounds, and Mixtures

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