Separating Mixtures

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Iron ore undergoing smelting.

Iron ore undergoing smelting.

 

We have already learned that most substances do not occur as pure substances but rather occur in mixtures. There are many ways to separate the components of mixtures. For example, iron metal occurs naturally in the ground as iron ore. Iron ore is many iron and oxygen. A process to separate the oxygen from the iron is called smelting. Smelting is a process that involves incredibly high temperatures.

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We won’t deal with smelting in the high school or college laboratory. We will deal with other processes of separating mixtures including,

  1. Filtration
  2. Distillation
  3. Chromatography

 

We will save chromatography for a later lesson. Let’s take a look at filtration and distillation.

 

Filtration

Coffee filters only allow water to pass through and not the coffee grounds

Coffee filters only allow water to pass through and not the coffee grounds

Filtration is a process that mechanically or physically separates substances that are in a mixtures. Filtration is most commonly used to separate solids from liquids or gases. Generally, solids are much larger particles than the particles of liquids or gases. Filtration takes advantage of this size difference of these particles by passing the mixture over a surface that has holes that are small enough to allow only the liquid or gas through. A coffee filter is a great example of this process. The ground coffee cannot pass through the paper filter, however, the water can pass through.

 

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Distillation

Distillation separates mixtures based on their boiling points.

Distillation separates mixtures based on their boiling points.

 

Distillation is a process that is generally used to separate homogeneous liquid mixtures. Distillation separates mixtures based on the different boiling points of the substances within the mixture. An example of a homogeneous mixture that could be separated with distillation would be a mixture of salt and water. If you were to put the mixture in a pot and heat the mixture until the water started to boil you would be able to notice steam rising from the mixture. This steam could be collected and cooled back into water and it would be pure water. Why didn’t any salt boil along with the water? Well the boiling point of water is 100 degrees Celsius while the boiling point of table salt is more than 1400 degrees Celsius. The mixture wouldn’t get hot enough for the table salt to boil and so all that would remain in the pot would be the table salt.

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