『新东方在线托福听力』为托福考生准备了ETS托福TPO/Official 45 Lec 3听力练习：Why does the professor mention the freezing point of a mixture?原文题目答案解析，TPO/Official 45 Lec 3听力原文范文音频翻译。

托福TPO/Official 45 Lec 3听力原文Why does the professor mention the freezing point of a mixture?【新东方在线】

旁白：请听一段化学课的讲座。

Narrator: Listen to part of the lecture in a chemistry class.

教授：总的来说，物质都是有质量和体积的，是吗？

Professor: So just to sum up, matter is anything that has mass and volume, right?

And this includes solids, liquids and gases.

如果我们把两种物质结合在一起，我们会得到一个混合物。

And if we combine two portions of matter, we get a mixture.

现在，有两种主要的混合物：同质和异质。

Now, there are two main kinds of mixtures: homogeneous and heterogeneous.

也许我应该把它们写在黑板上。

一个混合物是同质的，还是异质的……额……这就涉及到“相”的概念。

Whether a mixture is homogeneous or heterogeneous... well... this relates to the notion of “phase”.

记住，我们将“相”定义为一种物理状态，无论是固体，液体还是气体，都具有明确的边界和相同的特质。

Remember we defined the word “phase” as being one physical state, whether solid, liquid or gas, that... well... that has distinct boundaries and uniform properties.

所以，同质混合物是指的什么呢？

So homogeneous mixtures... What are they?

好的。前缀“homo-”表示“相同”。

Okay. The prefix “ homo- ” means “ same ”.

所以同质混合物是完全一样的。

So a homogeneous mixture is the same throughout.

所以如果你把酒精放在水里，两种液体结合。

So if you put alcohol in water, the two liquids combine.

你就再也察觉不到它们之间的任何边界了。

And you can't perceive any boundary between the two any longer.

即使它曾经包含两个相，但它现在只包含一个相，一旦将水和酒精混合在一起，你将难以分辨出它们。

Even though two phases went into it, it now contains one phase and we can't detect any boundary between the water and the alcohol once they're mixed together.

这两个部分组合形成一个单相。

The two portions combined form a single phase.

那么，如果同质混合物是完全相同的，异质混合物你们认为应该是什么呢？

Now, if homogeneous mixtures are ones that are the same throughout, then what do you suppose heterogeneous mixtures are?

对，异质混合物是完全不同的。

Right. Mixtures that are different throughout.

如果将油和水混合在一起，混合物包含两个液相，由于油的密度较低油所以会漂浮在水的顶部。

If you mix oil and water together, the mixture contains two liquid phases because the oil will float on top of the water because of the oil's lower density.

他们不会像酒精和水一样混合在一起。

They are not going to mix together like alcohol and water do.

你可以看到它们之间的界限，而且事实上，它们在物理上是可以分离的。

You can see the boundary between them and in fact, they are mechanically separable.

土壤作为固体材料的混合物也是如此。

The same is true for soil, which is a mixture of solid materials.

所以，如果仔细观察土壤样品，你会看到一点沙子，一些黑色物质，甚至些许植物的碎片。

So if you look closely at a sample of soil, you are going to see bits of sand, some black matter, maybe even pieces of vegetation.

因为你可以看到其中所有不同的组成部分，观察到不同物质的界限，所以它包含多个相。

Since you can see all the different components, detect distinct boundaries, we've got multiple phases.

事实上，你可以挑出各个部分。

And in fact, you can pick out the components.

这些不同的部分在物理上是可以分离的。

The various portions can be mechanically separated.

现在，在一些异质混合物中，你可以用肉眼看到不同的相。

Now, with some heterogeneous mixtures, you can see the different phases with the naked eye.

但是，并不是所有异质混合物都是如此，比如烟雾。

But that's not so for all of them, like smoke.

其实，这是一个很好的例子，因为肉眼看起来烟雾像是均匀的，就像它是单相的。

Actually, that's a good example because to the naked eye it looks uniform, like it's a single phase.

但如果你放大它，你可以看到有微小的固体和液体颗粒悬浮在空气中。

But if you magnify it, you can see that there are tiny solid and liquid particles suspended in the air.

所以实际上在烟雾中有三个相：固体，液体和气体，可以通过将其过滤逐一分离。

So actually what you got in smoke are three phases: solid, liquid, and gas, which you can separate by a process of filtration.

再举一个例子，比如脏水，好吗？

脏水是其中悬浮有固体物质的水。

Dirty water is water that has suspended solid matter in it.

让它通过一个过滤器，污垢和其他任何东西将留在滤纸后面。

Pass it through a filter and the dirt and whatever else is in there will stay behind in the filter paper.

And the clean water will pass through it.

同样，基于水中颗粒的尺寸，你可能也需要放大以后才能看到它们。

Again, depending on the size of the particles in the water, you might need magnification to see them.

但即使如此，他们也可以被观察到。

另一方面，对于同质混合物来说，无论怎样放大都无法显示出各组分之间可检测到的边界。

Homogeneous mixtures, on the other hand, well, no amount of magnification could reveal a detectable boundary between the components.

它们的混合一直延伸到基本粒子水平。

Their mixing extends all the way to the fundamental particle level.

我们使用术语“溶液”来表示单相，同质混合物。

And we use the term “solution” to refer to the single phase, homogeneous mixtures.

当盐溶解在水中时，再放大也无法显示检测出独立的盐颗粒。

When salts dissolve in water, no amount of magnification is going to show you separate pieces of salt.

盐和水之间没有可检测到的界限。

There are no detectable boundaries between salt and water.

即便如此，对于溶液，我们可以通过一种叫做蒸馏的方法，将各部分分离开来。

Even so, what you can do with solutions is separate the parts by a process called distillation.

如果你蒸馏盐水，水会从溶液中蒸发掉，只剩下盐。如果你蒸馏盐水，水从溶液中沸腾，只有盐留在后面。

If you distill salt water, water gets boiled away from the solution and only the salt remains behind.

在下一个实验中，我们将使用这些过程，蒸馏和过滤，来展示如何分离一些混合物的不同部分。

And in your next lab actually, we'll be using these processes, distillation and filtration, to show how we can separate the different parts of some mixtures.

现在，还有其他方法来描述混合物。

Now, there are other ways we can describe mixtures.

其中一个是通过属性，可变属性。

And one of these is by properties, uh, variable properties.

一个简单的例子是一杯咖啡的味道和颜色。

A real simple example of this is the taste and color of a cup of coffee.

溶解在水中的咖啡越多，咖啡的味道越强，颜色越深，溶液越黑。

The more coffee that's dissolved in the water, the stronger the taste of the coffee, and the darker the color, the darker the solution.

所以，颜色和味道，这两个可变属性。

So, color and taste, these are two variable properties.

这些可变属性会变化，当然，是由于各组分的相对含量不同，液体的熔点或凝固点也会不同。

And these variable properties, they vary of course, because of the relative amounts of the components, and the melting or freezing points of liquids too.

例如，盐水溶液具有不同的凝固点取决于溶解在水中的盐量。

A solution of salt water, for example, will have a different freezing point depending on how much salt is dissolved in the water.

In the lecture, the professor gives examples of homogeneous and heterogeneous mixtures. For each mixture below, indicate which kind it is.

What is one basis for classifying a mixture as homogeneous or heterogeneous?

What can be inferred from the lecture about the process of distillation?

Why does the professor mention the freezing point of a mixture?

What does the professor imply when he says this:

Listen to part of a lecture in a chemistry class. 
So just to sum up, matter is anything that has mass and volume, right? Anything that takes up space and this includes solids liquids and gases. And if we combine two portions of matter, we get a mixture. Now there are two main kinds of mixtures: homogeneous and heterogeneous, maybe I should put this on the board. 
Whether a mixture is homogeneous or heterogeneous, well, this relates to the notion of phase. Remember we defined the word phase as being one physical state whether solid liquid or gas. That well it has distinct boundaries and uniform properties. So homogeneous mixtures, what are they? 
Okay, the prefix homo means same. So homogeneous mixture is the same throughout. It contains only one phase. So if you put alcohol and water, the two liquids combine, they disperse into each other. And you can't receive any boundary between the two any longer. So the mixture contains only one phase, even though two phases went into it. It now contains one phase and we can't detect any boundary between the water and the alcohol once they're mixed together. The two portions combined to form a single phase. 
Now if homogeneous mixtures are ones that are the same throughout? Then what do you suppose heterogeneous mixtures are? Right, mixtures that are different throughout. If you mix oil and water together, to make sure it contains two liquid phases because the oil will float on top of the water because of the oils lower density. They're not going to mix together like alcohol and water do. You can see the boundary between them and in fact there a mechanically separable. The same is true for soil which is a mixture of solid materials. So if you look closely at the sample soil, you’re going to see bits of sand some black matter maybe even pieces of vegetation. Since you can see all the different components, detect distinct boundaries, we've got multiple phases, and in fact you can pick out the components the various portions can be mechanically separated. 
Now with some heterogeneous mixtures, you can see the different phases with the naked eye. But that's not so for all of them, like smoke. Actually that's a good example because to the naked eye, it looks uniform, like it's a single phase. But if you magnify it, you can see that there are tiny solid and liquid particles suspended in the air. So actually what you got in smoke are three phases: solid liquid and gas, which you can separate by a process of filtration. 
Another example, dirty water, okay? Dirty water is water that has suspended solid matter in it, that can be filtered too. Pass it through a filter and the dirt and whatever else is in there will stay behind on the filter paper, and the clean water will pass through it. Again, depending on the size of the particles in the water, you might need magnification to see them, but even so they can be detected. The boundaries are detectable. So multiple phases okay? 
Homogeneous mixtures on the other hand well no amount of magnification could reveal a detectable boundary between the components. Then mixing extends all the way to the fundamental particle level. And we use the term solution to refer to the single phase homogeneous mixtures. When salt dissolves in water, no matter magnification is going to show you separate pieces of salt. When salt there are no detectable boundaries between salt and water. So it's a solution. Even so what you can do with solutions is separate the parts by a process called distillation. If you distill saltwater, water gets boiled away from the solution and only the salt remains behind. And in your next lab actually will be using these processes, distillation and filtration, to show how we can separate the different parts of some mixtures. Now there are other ways that we can describe mixtures, and one of these is by properties, variable properties. Real simple example of this is the tasting color of a cup of coffee. The more coffee that’s dissolved in the water, the stronger the taste of the coffee, and the darker the color, the darker the solution. So color and taste, these are two variable properties. And these variable properties, they very of course, because of the relative amounts of the components. And the melting or freezing points of liquids too. A solution of salt water for example will have a different freezing point depending on how much salt is dissolved in the water.

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