📚 Separating Mixtures: Filtering and Decanting | 分离混合物：过滤与倾析
In KS3 chemistry, you learn that most materials around us are mixtures. A mixture contains two or more substances that are not chemically joined. This article focuses on two simple physical separation techniques: filtering and decanting. Both methods are used to separate an insoluble solid from a liquid, but they work in different ways and suit different situations.
在 KS3 化学中，你会了解到我们周围的大多数材料都是混合物。混合物含有两种或两种以上没有通过化学键结合的物质。本文重点介绍两种简单的物理分离技术：过滤和倾析。这两种方法都用于将不溶性固体从液体中分离出来，但它们的工作原理不同，适用的场合也不同。
1. Mixtures and Pure Substances | 混合物与纯物质
A pure substance is made of only one type of particle and has a fixed melting point and boiling point. A mixture contains at least two different substances that are physically combined, so its melting point is often not sharp.
纯物质只由一种粒子组成，具有固定的熔点和沸点。混合物至少含有两种不同的物质，它们只是物理混合，因此其熔点通常不固定。
Because the substances in a mixture are not chemically joined, we can usually separate them using physical methods such as filtering, decanting, evaporation, distillation, or magnetism.
由于混合物中的物质没有通过化学键结合，我们通常可以用过滤、倾析、蒸发、蒸馏或磁选等物理方法将它们分离。
Common examples of mixtures include:
- muddy water
- sand and salt
- air
- orange juice with pulp
常见的混合物例子包括：
- 泥水
- 沙子和盐
- 空气
- 带果肉的橙汁
2. Why Separation Matters | 为什么需要分离混合物
Separation is important in the laboratory and in everyday life. We may need to remove unwanted solid impurities from drinking water, recover a product after a reaction, or keep ingredients separate before use.
分离在实验室和日常生活中都很重要。我们可能需要去除饮用水中的不溶性固体杂质，回收反应后的产物，或在使用前将成分分开。
Choosing the right method depends on the physical properties of the substances, such as particle size, solubility, density, and boiling point.
选择正确的方法取决于物质的物理性质，例如颗粒大小、溶解性、密度和沸点。
For example, large particles can often be separated by decanting, while very fine particles may need filtering. Dissolved substances cannot be separated by either method.
例如，较大的颗粒通常可以用倾析分离，而非常细小的颗粒可能需要过滤。已溶解的物质则无法用这两种方法分离。
3. Insoluble Solids and Liquids | 不溶性固体与液体
An insoluble solid does not dissolve in a liquid. When it is mixed with a liquid, it forms a suspension that may look cloudy at first. Over time, many insoluble particles settle to the bottom under gravity.
不溶性固体不会溶解在液体中。当它与液体混合时，会形成起初看起来浑浊的悬浮液。随着时间推移，许多不溶性颗粒在重力作用下沉到底部。
If a solid dissolves, such as salt in water, the particles are too small to be caught by ordinary filter paper. Filtering cannot separate a dissolved solute from its solvent.
如果固体溶解了，例如盐溶于水，其粒子太小，普通滤纸无法截留。过滤不能将已溶解的溶质从溶剂中分离出来。
suspension → settled solid + liquid
This simple word equation shows that a suspension can separate into a settled solid and a clearer liquid if left still for a while.
这个简单的文字表达式说明，如果静置一段时间，悬浮液可以分离成沉降的固体和较澄清的液体。
4. Decanting: Letting Solids Settle | 倾析：让固体沉降
Decanting means carefully pouring off the liquid after a solid has settled to the bottom. It works best when the solid particles are heavy enough to settle quickly and stick together well.
倾析是指在固体沉降到底部后，小心地将液体倒出。当固体颗粒足够重、能快速沉降并且沉降得较紧实时，倾析效果最好。
The main advantage of decanting is that it is quick and requires no extra equipment. The main disadvantage is that some liquid may remain with the solid, and very fine particles may be poured off with the liquid.
倾析的主要优点是速度快，不需要额外设备。主要缺点是一些液体会残留在固体中，非常细小的颗粒也可能随液体被倒出。
A simple everyday example is pouring water off boiled rice or vegetables. The solid food stays at the bottom of the pan while the water is gently poured away.
一个简单的日常例子是倒掉煮米饭或蔬菜中的水。固体食物留在锅底，水被轻轻倒掉。
5. Filtering: Using a Filter to Trap Solids | 过滤：用过滤器截留固体
Filtering uses a barrier, such as filter paper, to trap insoluble solid particles while allowing the liquid to pass through. The liquid that passes through is called the filtrate.
过滤使用滤纸等屏障来截留不溶性固体颗粒，同时让液体通过。通过过滤器的液体称为滤液。
Filter paper has tiny holes, or pores. The pores are small enough to block most insoluble particles but large enough for water molecules and dissolved particles to pass through.
滤纸上有微小的孔。这些孔小到足以阻挡大多数不溶性颗粒，但又大到足以让水分子和溶解粒子通过。
Common equipment for filtering includes:
- filter funnel
- filter paper
- beaker or conical flask
- glass rod for guiding the liquid
过滤常用的设备包括：
- 过滤漏斗
- 滤纸
- 烧杯或锥形瓶
- 用于引流液体的玻璃棒
6. Key Terms: Filtrate and Residue | 关键术语：滤液和残渣
The filtrate is the clear liquid that passes through the filter paper and is collected in the container below. It should be free from insoluble solid particles.
滤液是通过滤纸并被收集在下方容器中的清澈液体。它应当不含不溶性固体颗粒。
The residue is the solid that remains on the filter paper. In a successful filtration, the residue stays behind while the filtrate drips through.
残渣是留在滤纸上的固体。在成功的过滤中，残渣被留下，滤液则滴下。
mixture → filtrate + residue
This word equation helps you remember the two products obtained when an insoluble solid is filtered from a liquid.
这个文字表达式可以帮助你记住将不溶性固体从液体中过滤出来时得到的两种产物。
In some experiments the filtrate is the useful part, while in others the residue is the desired product, such as a precipitate collected after a reaction.
在一些实验中，滤液是有用的部分；而在另一些实验中，残渣才是目标产物，例如反应后收集的沉淀。
7. Choosing Between Decanting and Filtering | 在倾析与过滤之间选择
Decanting is faster and simpler when the solid settles rapidly and you do not need to collect every drop of liquid. It is often used for large particles such as sand from water or tea leaves from tea.
当固体沉降较快，并且你不需要收集每一滴液体时，倾析更快、更简单。它常用于分离大颗粒，例如从水中分离沙子或从茶中分离茶叶。
Filtering is more effective when the solid is fine, cloudy, or must be completely removed from the liquid. It is also better if you want to keep both the solid residue and the clear filtrate.
当固体颗粒细小、液体浑浊或必须完全从液体中去除固体时，过滤更有效。如果你希望同时保留固体残渣和澄清滤液，过滤也更好。
For example, sand in water can be decanted after the sand settles, but chalk powder in water is better separated by filtering because chalk particles are very fine and may pour off with the water.
例如，水中的沙子沉降后可以倾析，但水中的粉笔末最好用过滤分离，因为粉笔颗粒非常细小，可能会随水一起倒出。
If you are not sure, ask yourself whether the solid particles stay at the bottom quickly or remain cloudy for a long time. Fast-settling solids are good for decanting; slow or cloudy mixtures usually need filtering.
如果你不确定，可以问自己：固体颗粒是很快沉到底部，还是长时间保持浑浊？快速沉降的固体适合倾析；沉降慢或浑浊的混合物通常需要过滤。
8. Laboratory Procedure for Filtering | 过滤的实验操作
To filter a mixture, first fold the filter paper to fit the funnel. Place the funnel in a clamp or in the neck of a conical flask. Pour the mixture slowly along a glass rod so the liquid runs onto the filter paper.
过滤混合物时，首先折叠滤纸使其适合漏斗。将漏斗放在铁架台的夹子上或锥形瓶口。用玻璃棒引流，将混合物缓慢地倒在滤纸上。
Never fill the funnel above the top edge of the filter paper. If you pour too quickly, solid particles may overflow and contaminate the filtrate.
切勿将漏斗中的液面加到滤纸顶端以上。如果倒得太快，固体颗粒可能溢出并污染滤液。
The usual steps are:
- fold the filter paper and place it in the funnel
- wet the paper with a little water so it sticks to the funnel
- pour the mixture slowly along a glass rod
- collect the filtrate in a clean beaker
通常的步骤如下：
- 折叠滤纸并放入漏斗
- 用少量水润湿滤纸，使其贴紧漏斗
- 沿玻璃棒缓慢倒入混合物
- 用干净的烧杯收集滤液
9. Everyday and Industrial Applications | 日常与工业应用
At home, decanting is used when pouring water off boiled vegetables or draining pasta. Filtering is used in coffee makers, tea strainers, and water filter jugs.
在家里，倒掉煮蔬菜的水或沥干意面时使用倾析。过滤用于咖啡机、滤茶器和滤水壶。
In water treatment plants, large settling tanks allow sand and mud to settle, then the clearer water is filtered through sand and gravel beds before further treatment.
在自来水处理厂中，大型沉淀池让沙子和泥浆沉降，然后较澄清的水通过沙石过滤床过滤，再进行进一步处理。
In the laboratory, both techniques help clean
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