Azeotrope - Definition, Types, Diagram Explanation, FAQs

Edited By Team Careers360 | Updated on Jul 02, 2025 04:54 PM IST

Define Azeotropes.

A constant boiling point mixtures are also known as an azeotropic mixture is a type of mixture consists of two or more liquids whose proportions can not be altered or changed by simple distillation. The concept is that when we boils an azeotropic mixture, the vapour state contains the same amount of the constituents as that of unboiled mixture. Generally the composition of an azeotropic mixture will not be changed through while undergoing distillation, azeotropes are known as constant boiling point mixture.

This Story also Contains

Define Azeotropes.
Q- Azeotropic Mixture Types ?
Q- What is Constant Boiling Mixture?
Q- What are Azeotropes Give an Example?
Types of Azeotropes:-
Q- Azeotrope phase diagram of Minimum - boiling or Positive azeotrope ?
Here is the phase diagram of Maximum - boiling or Negative azeotrope
Diagram Explanation :-

Q- Azeotropic Mixture Types ?

Minimum boiling azeotropic mixtures are the one that will boils at a temperature lower than the boiling point of other components in the pure state. The process of boiling and recondensation within a mixture of two solvents are due to the changes in chemical state. If the pressure will be held constant then the two variable parameters will be temperature and the composition. And, Maximum boiling azeotropes are those mixtures which shows the boiling point higher than any of its mixture constituents. In case of azeotrope the boiling point of the mixture will be higher than the constituents from which it is formed.

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Q- What is Constant Boiling Mixture?

A constant boiling point mixtures are also known as an azeotropic mixture is a type of mixture consists of two or more liquids whose proportions can not be altered or changed by simple distillation. According to Raoult's law it is used to predicts the vapour pressures of an ideal mixtures with a function of composition ratio. In respect to Raoult's law the molecules that are present within azeotropic mixture will stick to each other at the same degree that they stick within themselves.

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To understand we can take a look to this example, if the constituents of the mixture are X and Y, and X joins with Y with roughly equal energy as X joins with X and Y joins with Y or X – X & Y- Y. And thus this condition will be called as positive deviation from Raoult's law in which the constituents would have a disaffinity for each others as like X will sticks to X and Y will sticks to Y better than that of X sticks to Y. And the participants of the mixture that are having less total affinity within the molecules than of the pure constituents, they are more readily escape from the stuck i.e. together phase. And another case when X sticks to Y with aggressively force than that of X interact with X and Y interact with Y, then the result is known as a negative deviation according to Raoult's law.

In this case the molecules that are present within the mixture will interact more than that are present in the pure constituents, so that they need more energy to escape from the interaction i.e. liquid phase. And whenever the deviation may be able to cause a maximum or minimum change to its vapour pressure or composition function, then there will be a mathematical consequence that at that point, the vapour will constitute the same composition as that of the liquid, and thus resulting in an azeotrope.

Also, students can refer,

Q- What are Azeotropes Give an Example?

In the case of mixtures of chemicals that have similar solvents for example n-hexane with n-heptane, form almost ideal mixtures that comes very close to follow Raoult's law. We can easily notice that whenever a mixture that will shows a positive deviation must have a point at which the tangent is horizontal, then the composition at that point will be in a positive azeotrope. At that point the total vapour pressure will be at its maxima.

Q- What are Azeotropes?

A constant boiling point mixtures are also known as an azeotropic mixture is a type of mixture consists of two or more liquids whose proportions can not be altered or changed by simple distillation

Types of Azeotropes:-

There are two types of azeotropic mixtures i.e. positive azeotrope or minimum boiling azeotrope and negative azeotrope or maximum boiling azeotrope. Minimum - boiling also known as Positive azeotrope . Minimum boiling azeotropes are those mixtures that will boils at a temperature lower than the boiling point of other components in the pure state. The process of boiling and recondensation within a mixture of two solvents are due to the changes in chemical state. If the pressure will be held constant then the two variable parameters will be temperature and the composition.

Q- Azeotrope phase diagram of Minimum - boiling or Positive azeotrope ?

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Related topics ,

Maximum-boiling also known as Negative azeotrope

Maximum boiling azeotropes are those mixtures which shows the boiling point higher than any of its mixture constituents. In case of azeotrope the boiling point of the mixture will be higher than the constituents from which it is formed.

Here is the phase diagram of Maximum - boiling or Negative azeotrope

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Diagram Explanation :-

Each azeotrope held a characteristic boiling point. The boiling point of an azeotrope mixture had two probabilities that it may be less than the boiling point temperature compared to the other constituents i.e. known as a positive azeotrope, or its boiling point of azeotropic mixture will be greater than the boiling point of any of its constituents i.e. known as a negative azeotrope.

When an boils an azeotropic mixtures, then the vapour content of the mixture will be in the same proportions to the constituents as that of unboiled mixture. Generally the composition of an azeotropic mixture will not be changed through while undergoing distillation, azeotropes are known as constant boiling point mixture.

A general example for a positive azeotrope is the mixture of ethanol and water. As we can observe that boiling point of Ethanol is 78.4 °C, and water boils at 100 °C, but the azeotropic mixture will boils at 78.2 °C, we can notice here that mixture has lower boiling point than either of its two constituents. And it shows that 78.2 °C is the minimum temperature at which any of the two constituent i.e. ethanol or water solution can boils at atmospheric pressure.

A positive azeotrope will be boils at a temperature that will be lower than any of the other boiling point ratio of its constituents. Positive azeotropes are also known as minimum boiling mixtures or pressure maximum azeotropes.

While a negative azeotrope must be boiled at a temperature that is higher compared to the other constituents. Negative azeotropes is referred to be maximum boiling mixtures or pressure minimum azeotropes. General example to understand negative azeotrope is that when hydrochloric acid and water forms azeotropic mixture.

To note here that boiling point of Hydrogen chloride is 84 °C and that of water is 100 °C, but the azeotropic mixture have the boiling point of 110 °C, which comprises higher than either of its two constituents. And it shows that, the maximum temperature at which any of the hydrochloric acid solution can boils will be 110 °C. Other examples:

Mixture of sulfuric acid and water
Mixture of nitric acid and water
Mixture of perchloric acid and water.
Mixture of hydrofluoric acid and water

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NCERT Chemistry Notes:

Frequently Asked Questions (FAQs)

1. Mention the types of azeotrope.

There are two types of azeotropes. They are,

Minimum boiling azeotrope
Maximum boiling azeotrope.

2. What is the azeotrope of water and ethanol?

The azeotrope mixture contains 95.63% ethanol and 4.37% water.

3. Is azeotrope a compound?

Yes, it is a mixture of compounds having the same composition in vapor and liquid state.

4. What are the two types of azeotropes?

The two types of azeotropes are negative azeotrope and positive azeotropes.

5. Give one example of negative azeotropes?

Hydrochloric acid and water.

6. What is an azeotrope?

An azeotrope is a mixture of two or more liquids whose composition remains constant during distillation because the vapor has the same proportions of constituents as the liquid mixture. This occurs because the mixture behaves as if it were a single substance with a fixed boiling point.

7. What is a zeotropic mixture and how does it differ from an azeotrope?

A zeotropic mixture is one that can be completely separated by distillation, unlike an azeotrope. In a zeotropic mixture, the composition of the vapor phase is always different from the liquid phase, allowing for separation through multiple distillation stages. Azeotropes, on the other hand, have a point where vapor and liquid compositions are identical, preventing complete separation.

8. How do you identify an azeotrope on a boiling point composition diagram?

On a boiling point composition diagram, an azeotrope appears as a point where the liquid and vapor composition lines meet. This point represents the composition at which the mixture boils at a constant temperature, and the vapor has the same composition as the liquid.

9. Why can't azeotropes be separated by simple distillation?

Azeotropes can't be separated by simple distillation because the vapor and liquid compositions are identical at the azeotropic point. This means that no matter how many times you distill the mixture, you'll always end up with the same composition in both the distillate and the residue.

10. What is the significance of azeotropes in industrial processes?

Azeotropes are significant in industrial processes because they can limit the purity achievable through distillation. Understanding azeotropes is crucial for designing separation processes, especially in the chemical and pharmaceutical industries where high-purity products are required.

11. How does pressure affect azeotropic compositions?

Pressure can significantly affect azeotropic compositions. Changing the pressure can alter the boiling points of the components differently, potentially breaking the azeotrope or shifting its composition. This property is often used in techniques like pressure-swing distillation to separate azeotropic mixtures.

12. How do hydrogen bonds influence azeotrope formation?

Hydrogen bonds can significantly influence azeotrope formation by altering the intermolecular forces between components. Strong hydrogen bonding can lead to positive deviations from Raoult's law, potentially resulting in minimum boiling azeotropes. Conversely, the absence of hydrogen bonds between components that normally form them can lead to maximum boiling azeotropes.

13. What is a negative azeotrope?

A negative azeotrope, also called a maximum boiling azeotrope, is a mixture that boils at a temperature higher than either of its pure components. This happens because of stronger intermolecular forces between the different molecules in the mixture, making it harder for them to enter the vapor phase.

14. How does the presence of an azeotrope affect fractional distillation?

The presence of an azeotrope limits the effectiveness of fractional distillation. Once the azeotropic composition is reached, further separation becomes impossible using this method alone. This is because the vapor and liquid compositions are identical at the azeotropic point, preventing any additional purification.

15. How does Raoult's law relate to azeotropes?

Raoult's law describes the relationship between vapor pressure and composition in ideal mixtures. Azeotropes represent deviations from Raoult's law. Positive deviations (where the actual vapor pressure is higher than predicted) can lead to minimum boiling azeotropes, while negative deviations can result in maximum boiling azeotropes.

16. What is the role of intermolecular forces in azeotrope formation?

Intermolecular forces play a crucial role in azeotrope formation. Strong attractive forces between different molecules can lead to negative deviations from Raoult's law and maximum boiling azeotropes. Conversely, weak interactions or repulsive forces can cause positive deviations and minimum boiling azeotropes.

17. How do you calculate the boiling point of an azeotrope?

The boiling point of an azeotrope can be calculated using vapor-liquid equilibrium data. This typically involves constructing a temperature-composition diagram, finding the point where the vapor and liquid compositions are equal, and determining the corresponding temperature. Advanced thermodynamic models may be needed for accurate predictions.

18. Can you explain what a positive azeotrope is?

A positive azeotrope, also known as a minimum boiling azeotrope, is a mixture that boils at a temperature lower than either of its pure components. This occurs due to increased intermolecular forces between the different molecules in the mixture, making it easier for them to escape into the vapor phase.

19. How can azeotropes be broken or separated?

Azeotropes can be broken or separated using various techniques, including:

20. What is azeotropic distillation?

Azeotropic distillation is a separation technique used to break azeotropes by adding a third component (entrainer) to the mixture. The entrainer forms a new azeotrope with one of the original components, allowing for separation. After separation, the entrainer is typically removed and recycled.

21. What is the significance of the azeotropic point on a phase diagram?

The azeotropic point on a phase diagram represents the composition and temperature where the liquid and vapor phases have identical compositions. This point is significant because it marks the limit of separation achievable by simple distillation and indicates where the behavior of the mixture changes.

22. How do azeotropes affect the design of industrial separation processes?

Azeotropes significantly impact the design of industrial separation processes by:

23. What is a pseudo-azeotrope?

A pseudo-azeotrope is a mixture that behaves similarly to an azeotrope but doesn't have a true azeotropic point. Instead, the boiling point curves of the components come very close together, making separation by distillation extremely difficult but not theoretically impossible. Pseudo-azeotropes often require specialized separation techniques similar to those used for true azeotropes.

24. How do azeotropes impact the selection of entrainers in extractive distillation?

Azeotropes significantly influence the selection of entrainers in extractive distillation:

25. What is the difference between a minimum boiling azeotrope and a eutectic mixture?

While both minimum boiling azeotropes and eutectic mixtures represent special compositions with unique properties, they differ in several ways:

26. What are some common examples of azeotropes?

Some common examples of azeotropes include:

27. How does the concept of relative volatility relate to azeotropes?

Relative volatility is a measure of the difference in volatilities between two components in a mixture. For an azeotrope, the relative volatility becomes 1 at the azeotropic composition, meaning both components have equal tendencies to vaporize. This equality in volatility is what makes separation by simple distillation impossible at the azeotropic point.

28. How do azeotropes impact the efficiency of industrial distillation columns?

Azeotropes impact the efficiency of industrial distillation columns by:

29. What is the role of activity coefficients in azeotrope formation?

Activity coefficients play a crucial role in azeotrope formation by quantifying the non-ideal behavior of mixtures. They represent the deviation of a component's actual behavior from its ideal behavior in a solution. In azeotropes:

30. How does the concept of excess Gibbs energy relate to azeotrope formation?

Excess Gibbs energy is a thermodynamic property that quantifies the deviation of a mixture from ideal behavior. It relates to azeotrope formation in several ways:

31. How does an azeotrope differ from a regular mixture?

Unlike regular mixtures, azeotropes cannot be separated by simple distillation. In a regular mixture, the components have different boiling points and can be separated, while an azeotrope boils at a constant temperature and maintains its composition throughout the distillation process.

32. What is the azeotropic composition?

The azeotropic composition is the specific ratio of components in an azeotropic mixture where the vapor and liquid phases have identical compositions. This composition remains constant during distillation and represents the point where separation by simple distillation becomes impossible.

33. How do azeotropes affect the design and operation of reactive distillation processes?

Azeotropes can significantly impact reactive distillation processes by:

34. What are the two main types of azeotropes?

The two main types of azeotropes are:

35. What is the difference between homogeneous and heterogeneous azeotropes?

Homogeneous azeotropes form a single liquid phase, while heterogeneous azeotropes separate into two liquid phases. Heterogeneous azeotropes are easier to separate because the two liquid phases have different compositions, allowing for techniques like liquid-liquid extraction.

36. What is a ternary azeotrope?

A ternary azeotrope is an azeotrope formed by three different liquid components. Like binary azeotropes, ternary azeotropes have a constant boiling point and composition, but they involve a more complex equilibrium between three substances instead of two.

37. What is the importance of understanding azeotropes in the pharmaceutical industry?

Understanding azeotropes is crucial in the pharmaceutical industry for several reasons:

38. How do azeotropes affect the choice of solvents in chemical processes?

Azeotropes influence solvent choice in chemical processes by:

39. How can molecular simulation techniques be used to predict azeotrope formation?

Molecular simulation techniques, such as molecular dynamics and Monte Carlo simulations, can be used to predict azeotrope formation by:

40. What are some industrial applications where azeotropes are intentionally used or created?

While azeotropes often pose challenges in separation processes, they can also be intentionally used or created in some industrial applications:

41. How does the addition of a salt affect an azeotrope?

Adding a salt to an azeotropic mixture can alter the vapor-liquid equilibrium by changing the activity coefficients of the components. This can potentially break the azeotrope or shift its composition, making separation easier. This technique is known as salt-effect distillation.

42. How does the presence of an azeotrope affect the energy requirements of a separation process?

The presence of an azeotrope typically increases the energy requirements of a separation process because:

43. What is the relationship between azeotropes and vapor-liquid equilibrium (VLE) diagrams?

Vapor-liquid equilibrium (VLE) diagrams visually represent the relationship between liquid and vapor compositions in a mixture. Azeotropes appear on these diagrams as points where the liquid and vapor composition lines intersect, indicating identical compositions in both phases. VLE diagrams are essential tools for understanding and predicting azeotropic behavior, helping to design appropriate separation strategies.

44. What is the significance of the tangent pinch in relation to azeotropes?

The tangent pinch is a phenomenon in distillation where the operating and equilibrium lines become tangent to each other. In relation to azeotropes: