Name: suspensions, sedimentation, and colloids
Uploaded: 2023-06-23T15:38:43.000Z
Duration: 1 min 17 s
Channel: JoVE

Colóides e suspensões são misturas heterogêneas de dois ou mais componentes fisicamente misturados.
Em um colóide, o tamanho das partículas de soluto varia de 1 a 1000 nanômetros, pequeno o suficiente para serem invisíveis individualmente. No entanto, essas partículas de soluto podem espalhar a luz, fazendo com que os colóides pareçam translúcidos ou opacos. Eles permanecem na solução indefinidamente e não se acomodam.
O citosol, o material semifluido dentro das células vivas, é um colóide por causa das inúmeras proteínas e metabólitos dispersos nele.
Em contraste, as suspensões contêm partículas grandes, geralmente com mais de 10000 nanômetros, muitas vezes visíveis a olho nu.
Quando não perturbadas, essas partículas se depositam como sedimentos.
O sangue é um exemplo de suspensão. Quando o sangue recém-coletado não é perturbado por algum tempo, os glóbulos vermelhos se depositam no fundo do recipiente. A porção líquida superior, chamada plasma sanguíneo, é uma solução de pequenos solutos, bem como um colóide contendo proteínas plasmáticas maiores.

coloides e suspensões

As crianças brincando frequentemente acabam criando suspensões, como misturas de lama e água, farinha e água, ou uma suspensão de pigmentos sólidos em água conhecida como tinta têmpera. Essas suspensões são misturas heterogêneas compostas por partículas relativamente grandes, visíveis a olho nu ou que podem ser vistas com uma lupa. Elas são turvas, e as partículas suspensas se depositam depois da mistura ficar parada. As partículas suspensas em uma suspensão se depositam após algum tempo de mistura. A separação das partículas de uma suspensão é chamada sedimentação. Um exame de sangue para determinar a taxa de sedimentação mede quão rapidamente as células vermelhas do sangue em um tubo de ensaio se separam da porção aquosa do sangue (conhecida como plasma) ao longo de um período de tempo determinado. A sedimentação rápida das células sanguíneas normalmente não ocorre em um corpo saudável. Por outro lado, as características de certas doenças podem fazer com que as células sanguíneas se agrupem, e esses agrupamentos pesados de células sanguíneas se depositam no fundo do tubo de ensaio mais rapidamente do que as células sanguíneas normais.

Outra classe de misturas conhecidas como coloides (ou dispersões coloidais) apresentam propriedades intermediárias entre as de suspensões e soluções. As partículas em um coloide são maiores do que a maioria das moléculas simples; no entanto, as partículas coloidais são pequenas o suficiente para não se depositarem ao ficarem em repouso. As partículas em um coloide são grandes o suficiente para dispersar a luz, um fenômeno chamado efeito Tyndall; e é por isso que as misturas coloidais parecem turvas ou opacas, como os feixes de luz de holofotes. Nuvens também são misturas coloidais. Elas são compostas por gotículas de água muito maiores do que moléculas, mas pequenas o suficiente para não se depositarem. Alguns coloides têm a propriedade de passarem por transformações sol-gel, podendo se transformar, de forma reversível, de um estado fluido para um estado sólido (gel). Por exemplo, produtos de gelatina se solidificam para formar um gel quando refrigerados, mas que podem ser liquefeitos novamente quando aquecidos. A propriedade sol-gel do citossol, o fluído das células vivas, é essencial para muitas atividades celulares, como a divisão celular ou a mudança na forma das células. O componente de partículas de uma solução coloidal, presente em uma quantidade relativamente menor, é chamado de fase dispersa. A substância, ou solução, na qual o particulado está distribuído, é chamada de meio disperso.

Este texto foi adaptado de <a href="https://openstax.org/books/anatomy-and-physiology-2e/pages/2-4-inorganic-compounds-essential-to-human-functioning">Openstax, Anatomy and Physiology 2e, Section 2.4: Inorganic Compounds Essential to Human Functioning</a> and <a href="https://openstax.org/books/chemistry-2e/pages/11-5-colloids">Openstax, Chemistry 2e, Section 11.5: Colloids</a>.

Coloides e Suspensões

As crianças brincando costumam fazer suspensões como misturas de lama e água, farinha e água, ou uma suspensão de pigmentos sólidos em água conhecida como têmpera ...

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Colloids and Suspensions

suspensions, sedimentation, and colloids

Suspensions and colloids are two common kinds of mixtures seen in everyday life. Mud and water, flour and water, and tempera paint are suspensions. These mixtures are heterogeneous, which means their particles are not spread out evenly. The particles are relatively large and can be seen with the naked eye or a magnifying glass.

Suspension particles make mixtures cloudy, and they settle out after mixing. The settling of particles in a suspension is called sedimentation. A blood test can measure the rate of sedimentation by showing how fast red blood cells settle out of plasma, the watery part of blood, in a test tube over time. Rapid sedimentation is not usual in a healthy body, but some diseases can cause blood cells to clump together and sink faster than normal cells.

Colloids, also called colloidal dispersions, sit between suspensions and solutions. Their particles are larger than most simple molecules, but they are small enough that they do not settle out when left standing. Colloidal particles are still large enough to scatter light. This is known as the Tyndall effect, and it makes colloids look cloudy or opaque, like a beam from a searchlight.

Clouds are another example of a colloid. They contain water droplets that are bigger than molecules, but still small enough to stay suspended in the air. Some colloids can also change from a fluid sol to a solid gel and back again. Gelatin is one example. It forms a gel when chilled and can become liquid again when heated. The sol-gel behavior of cytosol, the fluid inside living cells, is important for cell division and for changes in cell shape.

In a colloid, the dispersed phase is the particulate part present in smaller amount. The dispersion medium is the substance that carries the particles throughout the mixture. These terms help describe how colloids are organized and why they behave differently from suspensions and solutions.

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Suspensions, Sedimentation, and Colloids

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