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Steam Distillation is a particular type of separation process for substances that are temperature sensitive. The only difference between steam distillation and normal distillation is that, along with the substance to be distilled, steam is also used in the distilling jar. At high temperatures, some organic compounds may decompose. Normal distillation can’t be used as it becomes difficult to separate the substances after reaching their boiling points. Thus, steam distillation is used for separating miscible liquid bases depending upon their volatilities as it allows substances to vaporize below their boiling point.
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Key terms: Steam distillation, vaporize, volatile, miscible, organic compounds, mixture.
Working and Principle of Steam Distillation:
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Steam Distillation works on the principle that, when two immiscible mixtures are heated together, each liquid exerts its, despite the presence of the other substance, and the vapour pressure in the system increases tremendously. This happens due to the combination of the sum of the vapour pressures of all the components of the mixture.
The two immiscible liquids start boiling when the vapour pressure of these liquids crosses the atmospheric pressure. Thus, the elements having high boiling points start evaporating at lower temperatures and form a mixture with water. Many organic compounds are insoluble in water. Thus, at an absolute temperature, they can be separated below their decomposition point.
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Steam Distillation Extraction Procedure:
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In the Extraction process of the compounds, a stream of strong steam is passed through the apparatus containing the organic compounds that are to be separated. If the steam is condensed then form a mixture of matter & Steam. More steam is further passed through the mixture. The mixture gets heated up and starts boiling. The vapour pressure starts reducing which leads to the evaporation of the necessary organic compounds. Thus, the extraction takes place from organic matter.
Steam Distillation Separation Procedure:
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In the separation procedure, the mixture of steam and organic compounds that had been evaporated is passed through a container with cold water in it at one end. Further, the same mixture passes through hot water at the other end. Thus, condensation of the mixture takes place.
Further, the mixture is collected and taken for separation. During the settling process, the extracted compounds come to the top and are thus filtered out from the water below.
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Process of extraction of essential oils by steam distillation
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Steam distillation is an easy and efficient way to extract aromatic compounds in the form of essential oils from plants species. Steam is gently released into the apparatus and allowed to flow through the plant matter. This low-pressure steam allows to replace the volatile compounds and helps release the oil.
The lid of the apparatus prevents the oil from passing out into thin air. Further, the oil and water that pass through the water are separated and collected.
Applications of Steam Distillation:
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- Steam distillation is widely used in the manufacturing of essential oils and perfumes. Mainly orange oil and eucalyptus oil are extracted using this method.
- It is also used during consumer food products produced to the separation of fatty acids from the component of the mixture.
- A modification of steam distillation is also used for the isolation of dairy flavours from dairy products.
- Steam distillation is widely used in the petroleum industry. Also, for the separation of components from crude oil, steam distillation is used.
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Advantages of Steam Distillation:
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- It doesn’t require much fuel and energy
- It doesn’t need high maintenance equipment and is quite economic
- It generates organic solvent-free products
- Extraction of essential oils can be done easily
Things to Remember:
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- Steam Distillation is used for the extraction of aromatic compounds from plant species
- It is also used for the purification of organic compounds that are temperature sensitive and can decompose.
- Steam Distillation is used to purify the impure liquid by passing steam and is applicable under specific conditions only.
- Steam Distillation is dependent on vapour pressure.
- The only difference between steam distillation and normal distillation is that, along with the substance to be distilled, steam is also used in the distilling jar.
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Sample Question:
Ques. Many organic compounds are insoluble in ___________. [01 Marks]
1. Ether
2. Water
3. Alcohol
4. Benzene
Ans. B) Water
Explanation: All organic compounds of alkanes, alkenes, alkynes, alkyl halides have low solubility in water. Alcohols, carboxylic acids, amines, esters are usually soluble in water. But, when those compounds’ molecular mass increases, solubility in water is decreased. Thus, most organic compounds are insoluble in water.
Ques. What is Steam distillation is mainly dependent on? [01 Marks]
1. Melting point
2. Boiling point
3. Vapour Pressure
4. Temperature
Ans. C) Vapour Pressure
Explanation: when two immiscible mixtures are heated together, each liquid exerts its, despite the presence of the other substance, and the vapour pressure in the system increases tremendously. The two liquids start boiling and the vapour pressure of these liquids outplace the atmospheric pressure. Thus, steam distillation is mainly dependent on vapour pressure.
Ques. Which process is used for removing organic compounds from plant pieces? [01 Marks]
1. Steam Distillation
2. Sublimation
3. Decantation
4. Condensation
Ans. A) Steam Distillation
Explanation: At a high temperature, some organic compounds decompose. Thus, steam distillation is a reliable method for removing organic compounds from plant species and extracting aromatic hydrocarbons.
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Q4. Steam Distillation is a separation process for substances that are sensitive to ________? [01 Marks]
1. Temperature
2. Pressure
3. Volume
4. Mass
Ans. A) Temperature
Explanation: At high temperatures, some of the organic compounds may decompose. For the separation of such temperate sensitive substances, steam distillation is used, as it allows the compounds to vaporise below their boiling point.
Ques. Why does an organic liquid vaporise at a temperature below its boiling point in its steam distillation? [02 Marks]
Ans. In steam distillation, the organic liquid starts to boil when the sum of vapour pressure due to the organic liquid (p1) and the vapour pressure due to water (p2) becomes equal to atmospheric pressure (p),
that is, p = p1 + p2
Since p1 < p2, the organic liquid will vaporise at a lower temperature than its boiling point.
Ques. How is steam distillation different from simple distillation? [03 Marks]
Ans. The only difference between steam distillation and basic distillation is that, along with the substance to be distilled, steam (or water) is used in the distilling jar. And, steam distillation is used over basic distillation as it allows the compounds to vaporise below their boiling point.
Ques. What is steam distillation used for? Give an example of a mixture that is separated using steam distillation. [02 Marks]
Ans. Steam distillation is used for the separation of two immiscible liquids below their decomposition points. It is also used for extracting aromatic compounds from plant species. A mixture of water and aniline is separated by steam distillation.
Read Also: Huckel Rule of Aromaticity
Ques. What is distillation? On which principle does distillation work? [03 Marks]
Ans. Distillation is a physical separation method based on the difference in boiling temperatures of the components of a solution. A mixture is heated to a specific temperature that evaporates one component of the solution, hence completely separating the two matters.
Distillation works on the principle of volatility difference of the individual components of the mixture.
Ques. Why is O-Nitrophenol more steam volatile than P-Nitrophenol? [03 Marks]
Ans. O-Nitrophenol forms intramolecular H bond whereas molecules of P-Nitrophenol get associated through intermolecular H bond. During boiling, the strong intermolecular H bonding increases the boiling point but intramolecular H bonding cannot do so. Therefore, O-Nitrophenol is more steam volatile than P-Nitrophenol.
Ques. What is the difference between distillation, fractional distillation and steam distillation? Give examples of where it is used. [05 Marks]
Ans.
1) Distillation: This process is used to separate liquids with a major difference in their boiling points. Distillation is used in the case of volatile liquids with non-volatile impurities. It needs a simple experimental set-up with two simple flasks and a condenser. Used in the purification of seawater.
2) Fractional Distillation: This process is used to separate liquids with closer boiling points. In fractional distillation, multiple simple distillation processes are carried out with small losses in one. It requires a complex experimental setup with a fractioning column apparatus. Used in crude oil refining.
3) Steam Distillation: This process is used in the purification of temperature-sensitive substances. A liquid that decomposes on boiling can be purified by this method. The boiling point is lowered Under reduced pressure. This prevents decomposition. Used for separating water and aniline.
Ques. Write a note on Steam Distillation? [05 Marks]
Ans. Steam Distillation is a process is used in the purification of temperature-sensitive substances. This process is used to purify impure liquids. The mixture of impure liquids is passed through steam. It is only applicable under the following conditions.
- The liquid must be steam volatile but the impurities present must be non-volatile.
- The liquid must be immiscible with water.
- The liquid must possess sufficiently high vapour pressure at the boiling point temperature of water (373 K).
With the help of steam distillation, the liquids which have boiling points higher than the boiling point of water (373 K) can be distilled at a lower temperature under reduced pressure inside the flask. Thus, steam distillation is comparable to distillation under reduced pressure. This can be explained with the help of Dalton’s law of partial pressures as given below:
According to the law, the pressure exerted by a gaseous mixture in a container is equal to the sum of the partial pressures of the constituent gases provided they do not react chemically, i.e., P = P1 + P2.
Where P = Total pressure of the mixture (atmospheric pressure)
Pi = Vapour pressure of steam
P2 = Vapour pressure of the liquid vapours
The vapour pressure of the liquid inside the flask is less than P which is atmospheric pressure. Thus, the liquid boils under reduced pressure and gets distilled along with vapours of steam at a temperature lower than its boiling point temperature.
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