Types of Azeotropic Mixtures

A mixture is defined as a substance gotten from the physical combination of two or more other substances. A mixture is not chemically combined so it can be easily separated. Examples of mixtures include the following;

  1. Ink
  2. Gunpowder
  3. Sea Water
  4. Crude oil
  5. Kerosene and water 

Mixtures are said to be either homogeneous or heterogeneous.

Homogeneous Mixtures 

 Homogeneous mixtures are mixtures that can be in solid, liquid or gaseous forms and   have a uniform combination. These mixtures are said to have the same appearance and chemical composition. Examples of homogeneous mixtures are sea water, vinegar, brass, air, steel..etc.

Heterogeneous Mixtures

Heterogeneous mixtures are mixtures that lack uniform combination or composition, in other words, these are mixtures that are visually distinguishable. Examples of homogeneous mixtures are kerosene and water, oil and water, smog, water and salt, water and sand etc.

What is an Azeotrope?

The word Azeotrope is derived from the Greek word “a” which means “meaning not”, and the word “zeo” which means “boil”, and “tropic” which means change. This simply means that an azeotrope is a mixture that cannot be changed by distillation or boiling.

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What is an Azeotropic Mixture?

An azeotropic mixture is defined as mixtures of liquids with a constant boiling point having a vapor with the same composition as the liquid. Examples of azeotropes are as follows;

  1. The mixture of  methyl ether and halothane .
  2. The mixture of water and hydrogen chloride.
  3. The mixture of water and ethanol.
  4. The mixture of chloroform and water.
  5. The mixture of ethyl alcohol and water.

Types of Azeotropic Mixtures 

There are 5 different types of azeotropes and they include the following;

  1. Homogeneous azeotrope
  2. Heterogeneous azeotrope
  3. Binary azeotrope
  4. Ternary azeotrope
  5. Maximum boiling azeotrope or Positive Azeotrope Mixtures 
  6. Minimum boiling azeotrope or Negative Azeotrope Mixtures 

Homogeneous Azeotrope Mixtures 

Homogeneous azeotrope mixtures are mixtures that are completely miscible 

With each other. Examples of homogeneous azeotrope mixtures are; Butene, distillation columns,  dimethyl carbonate, ethanol, acetate, acetone.

Heterogeneous Azeotrope Mixtures 

The heterogeneous azeotrope mixture is a mixture where the vapor phase coexist with

the two liquids that make up the mixture . Examples of a heterogeneous mixture are toluene,  benzene, dichloromethane, and n-butanol. 

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Forms of Heterogeneous Azeotrope Mixtures 

Heterogeneous azeotrope mixtures are made up of two layers which are:

  1. An organic layer that contains pure n-butyl acetate which is saturated with water.
  2. An aqueous layer phase containing pure water which is saturated with saturated n-butyl acetate.

Binary Azeotrope Mixtures

The binary azeotrope mixture which happens to be a homogeneous mixture is a liquid having a maximum or minimum vapor pressure (P) at constant temperature (T).

Ternary Azeotrope Mixtures 

Azeotropes that consists of three constituents are called ternary azeotropes. Examples of such azeotropes are: acetone, methanol and chloroform.

Maximum Boiling Azeotrope Mixtures or Positive Azeotrope Mixtures

The maximum boiling point azeotrope mixtures are mixtures that boil at a higher temperature than the boiling point of each component in a pure state. An example of the maximum boiling point azeotrope mixture is the boiling point of hydrogen chloride which is -84°C and that of water which is 100°C but the mixture of the two substances form an azeotrope that boils at 100°C. 

Minimum Boiling Azeotrope or Negative Azeotrope

Minimum boiling point azeotropes are azeotropic mixtures that boil at a lower temperature than the boiling point of the components present in its pure state. An example of the minimum boiling azeotrope is the mixture of 95.5% ethyl alcohol and 4.5% water mass which forms a boiling point at a constant temperature of 78°C.

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Frequently Asked Questions About Azeotropes and Azeotropic Mixtures

Why is a mixture called an azeotrope or an azeotropic mixture?

A mixture is referred to, or called an azeotrope or an azeotropic mixture because it is a mixture of substances with the same concentration of vapor and fluid phases.

How do you differentiate an azeotropic mixture from a non-azeotropic mixture

An azeotropic mixture is a blend of two or more liquid substances with one boiling and condensing point for a given system pressure. While. A non-azeotropic also referred to as a “zeotropic” mixture is a mixture of two or more components with different boiling points.

How to know when a mixture is azeotrope

Azeotrope or azeotropic mixtures can have a higher or lower boiling point than the components of the mixture.