Name: steam distillation and low-boiling separation
Uploaded: 2020-03-26T07:22:28.000Z
Duration: 3 min 54 s
Channel: JoVE

عندما يتم تسخين خليط مثالي من سائلين قابلين للامتزاج حتى الغليان ، يغلي المحلول عند درجة حرارة بين نقاط الغليان لكل مكون. إذا كانت هذه السوائل لها نقاط غليان مختلفة جدا ، فعندما يبدأ الخليط في الغليان ، يكون البخار غنيا بجزيئات المكون الأكثر تقلابا. غالبا ما تستخدم هذه الظاهرة لفصل الخلائط باستخدام التقطير البسيط ، حيث يتم تسخين خليط من سائلين قابلين للامتزاج ثم يتم تكثيف البخار مرة أخرى إلى سائل وجمعه. 
عندما يتم جمع البخار الغني بالمكون الأكثر تقلبا على شكل نواتج التقطير ، تصبح المرحلة السائلة غنية بجزيئات المكون الأقل تقلابا. ومع ذلك ، تتطلب هذه التقنية تسخين المحلول على الأقل إلى درجة غليان المركب الأكثر تقلبا وغالبا ما يكون أبعد من ذلك. 
في حالة المركبات العضوية الحساسة لدرجة الحرارة ، يمكن أن تؤدي درجة الحرارة المرتفعة هذه إلى تحلل الجزيئات العضوية إلى شيء آخر. إذن، كيف يمكننا فصل هذه الأنواع من المركبات؟ أولا ، دعنا نعود خطوة إلى الوراء. 
تذكر أن ضغط البخار في حالة توازن مع مرحلته المكثفة يسمى ضغط البخار. لكل من مكونات خليط السوائل ضغط بخار خاص بها ، والذي نسميه ضغطها الجزئي. نحن نعلم أن المحلول يغلي عندما يكون ضغط بخار المحلول الكلي مساويا للضغط الجوي. ضغط البخار الكلي يساوي مجموع الضغوط الجزئية للمكونات. 
بالنسبة لخليط من السوائل القابلة للامتزاج ، مما يعني أن أي مزيج من السوائل يشكل محلولا متجانسا ، يتم حساب الضغوط الجزئية من ضغوط بخار المركبات النقية مضروبة في كسور الخلد في المحلول. ومع ذلك ، بالنسبة لمزيج غير متجانس من السوائل غير القابلة للامتزاج ، مما يعني أن السوائل غير قابلة للذوبان في بعضها البعض ، فإن الضغوط الجزئية هي ببساطة ضغوط بخار المركبات النقية. 
نظرا لأن كل مكون من مكونات الخليط غير المتجانس يساهم في ضغط البخار الكلي بشكل مستقل عن المكونات الأخرى ، فإن الخليط يغلي عندما يكون ضغط البخار الكلي ، وهو مجموع الضغوط الجزئية ، مساويا للضغط الجوي. يحدث هذا عند درجة حرارة أقل من نقاط الغليان الفردية لكل مكون لأن ضغط البخار الكلي يزداد مع درجة الحرارة بشكل أسرع بكثير مما تتوقعه حتى بالنسبة للمكون الأكثر تقلبا. 
يمكننا تسخير هذه الظاهرة لإجراء التقطير بالبخار ، والذي يستخدم لعزل مركب عضوي حساس لدرجة الحرارة يتحلل تحت حرارة عالية وغير قابل للذوبان في الماء من المواد غير المتطايرة. يشبه إعداد التقطير بالبخار إعداد التقطير البسيط مع إضافة خزان مياه لتجديد المياه طوال العملية. 
عندما يغلي الخليط ، يتبخر كل من الماء والمركب العضوي المهم. تنتقل أبخرة الماء والمركبات العضوية إلى المكثف ، ويتم تكثيفها إلى سائل ، ويتم جمعها. يتم فصل السوائل غير القابلة للامتزاج بعد ذلك. يتم ترك الماء والمواد غير المتطايرة فقط في الخليط في القارورة. 
في هذا المختبر ، ستقوم بإعداد وإجراء تجربة تقطير بالبخار لاستخراج الزيت العطري من المكونات غير المتطايرة لقشر البرتقال. ستستخدم بعد ذلك الاستخراج السائل السائل لاستخراج الزيت العطري من الماء إلى مذيب عضوي.

التقطير بالبخار

Steam Distillation

<h4>التقطير بالبخار </h4>
التقطير بالبخار هو تقنية فصل تسخر خاصية نقطة الغليان المنخفضة للمخاليط غير القابلة للامتزاج. يتم استخدامه في الغالب لفصل الجزيئات العضوية الحساسة لدرجة الحرارة عن الملوثات غير المتطايرة. يجب أن يكون الجزيء العضوي غير قابل للامتزاج في الماء. 
في التقطير بالبخار ، يتم تسخين الخليط غير القابل للامتزاج حتى الغليان ، مما يتسبب في تقطير كل من الماء والمركبات العضوية المتطايرة. هذا يعني أن الخليط الغازي ينتقل لأعلى إلى مكثف ، والذي يقوم بعد ذلك بتكثيف البخار إلى سائل بحيث يمكن جمعه. على عكس التقطير البسيط ، يستخدم التقطير بالبخار خزان مياه لتجديد الماء في الخليط الساخن طوال العملية. يتم تقطير المكون العضوي غير القابل للامتزاج ببطء مع الماء ، بينما يبقى المكون غير المتطاير في الخليط الساخن. بمجرد تقطير المكون العضوي ، يمكن بعد ذلك فصله عن الماء باستخدام الاستخراج السائل السائل. 
<h4>ضغط بخار الخليط</h4>
بالنسبة للخليط القابل للامتزاج الذي يشكل محلولا متجانسا ، يعتمد ضغط بخار كل مكون على ضغط بخار المكون النقي وجزء الخلد في الخليط السائل وفقا لقانون راولت. 
pA = pA*xA
 حيث pA هو ضغط بخار مكون سائل واحد في خليط سائل قابل للامتزاج ، pA * هو ضغط بخار السائل النقي ، و x A هو جزء الخلد من هذا السائل في الخليط ، وهو ما يساوي nA/nt. nA هو عدد مولات السائل الفردي في الخليط، و nt هو العدد الكلي لمولات جميع السوائل في الخليط. 
ضغط البخار الكلي فوق خليط السائل القابل للامتزاج يساوي مجموع ضغط البخار الجزئي لكل مكون فيه ، والذي يعرف باسم قانون دالتون. يزداد ضغط بخار السائل مع درجة الحرارة حيث تكتسب المزيد من الجزيئات طاقة حركية للهروب من الطور السائل إلى الطور الغازي. في خليط قابل للامتزاج يحتوي على سائلين ، يمكن وصف الضغط الكلي على النحو التالي: 
P = pA + pB
 حيث pA و pB هي ضغوط بخار السائل A السائل B ، على التوالي ، فوق الخليط. P هو ضغط البخار الكلي لكلا السائلين فوق الخليط. يصف الجمع بين المعادلات العلاقة بين ضغط البخار الكلي للمحلول وجزء الخلد للمكونات الفردية:
P = pA*xA + pB*xB
في خليط غير قابل للامتزاج ، حيث تشكل المكونات خليطا غير متجانس ، تساهم ضغوط البخار لكل مكون بشكل مستقل في ضغط البخار الكلي. وبالتالي ، فإن ضغط البخار الكلي يساوي مجموع ضغوط البخار النقي الفردية. في خليط غير قابل للامتزاج يتكون من سائلين ، يتم تعريف الضغط الكلي على أنه ضغط بخار السائل الأول بالإضافة إلى ضغط بخار السائل الثاني. 
P = pA* + pB*
<h4>نقطة غليان خليط غير قابل للامتزاج</h4>
عندما يتم تسخين السائل ، يزداد ضغط البخار. كل مكون في الخليط له نقطة غليان خاصة به. في خليط من السوائل القابلة للامتزاج ، يحدث الغليان عند درجة حرارة بين نقاط غليان السوائل المكونة. 
بالنسبة للخليط غير القابل للامتزاج ، يحدث الغليان عند درجة حرارة أقل بكثير من نقاط غليان المكونات الفردية. نظرا لأن كل مكون فردي يساهم بشكل مستقل ، فإن هناك حاجة إلى حرارة أقل لزيادة ضغط البخار الكلي إلى الضغط الجوي. 
على سبيل المثال ، ضع في اعتبارك الخليط غير القابل للامتزاج من البنزين والماء. درجة غليان البنزين عند الضغط الجوي العادي هي 80.1 درجة مئوية ، ودرجة غليان الماء عند الضغط الجوي العادي هي 100 درجة مئوية. يغلي المحلول عندما يصل ضغط البخار الكلي إلى 760 مم زئبق (الضغط الجوي العادي). عند 69.3 درجة مئوية ، يبلغ ضغط بخار الماء 227 مم زئبق وضغط بخار البنزين 533 مم زئبق ، وهو ما يساوي في المجموع 760 مم زئبق اللازم المطلوب للغليان. هذا أقل بكثير من نقطة غليان أي من المكونات الفردية. 
<h4>المراجع</h4>
<ol>
	<li style="font-size:17px">كوتز ، جي سي ، تريتشيل جونيور ، بي إم ، تاونسند ، جي آر (2012). الكيمياء والتفاعل الكيميائي. بلمونت ، كاليفورنيا: بروكس / كول ، Cengage Learning. </li>
	<li style="font-size:17px">سيلدربيرج ، MS (2009). الكيمياء: الطبيعة الجزيئية للمادة والتغيير. بوسطن ، ماساتشوستس: ماكجرو هيل. </li>
</ol>

التقطير بالبخار 
التقطير بالبخار هو تقنية فصل تسخر خاصية نقطة الغليان المنخفضة للمخاليط غير القابلة للامتزاج. إنه في الغالب ...

Education

JoVE Lab Manual

Chemistry

الكيمياء

steam distillation and low-boiling separation

Steam distillation is a separation method for temperature-sensitive organic compounds. It works best when the organic compound is immiscible in water, meaning the two liquids do not mix. The method helps remove the organic molecule from a non-volatile contaminant without using the higher temperatures needed for many other separations.

In steam distillation, the immiscible mixture is heated until both water and the volatile organic compound distill together. The vapor rises to a condenser, where it cools and becomes a liquid that can be collected. Unlike simple distillation, this setup uses a water reservoir to keep replacing water in the heated mixture during the process.

The organic component is carried over slowly with the water, while the non-volatile component stays behind in the heated flask. After distillation, the organic product can be separated from the water by liquid-liquid extraction. This makes steam distillation useful for isolating sensitive organic materials from unwanted impurities.

The same low-boiling behavior can be explained by vapor pressure. For a miscible mixture, each liquid follows Raoult’s law, so its vapor pressure depends on the pure liquid vapor pressure and its mole fraction. The mole fraction is the number of moles of one liquid divided by the total number of moles in the mixture. The total vapor pressure above a miscible mixture follows Dalton’s law and equals the sum of the partial vapor pressures.

As temperature rises, vapor pressure increases because more molecules gain enough kinetic energy to escape into the gas phase. In a two-liquid miscible mixture, the total pressure can be written as P = pA + pB, or as P = pA*xA + pB*xB when Raoult’s law is included. In an immiscible mixture, the components act independently, so the total pressure is the sum of the vapor pressure of the first liquid and the vapor pressure of the second liquid.

This independent vapor-pressure behavior is why immiscible mixtures boil at lower temperatures than either pure liquid. In a miscible mixture, boiling usually happens between the boiling points of the components. In an immiscible mixture, less heat is needed to reach atmospheric pressure, so the boiling point drops well below the boiling points of the individual liquids.

A benzene-water mixture shows this effect clearly. Benzene boils at 80.1 °C, and water boils at 100 °C at normal atmospheric pressure. The mixture boils when the total vapor pressure reaches 760 mm Hg. At 69.3 °C, water contributes 227 mm Hg and benzene contributes 533 mm Hg, which adds up to 760 mm Hg. That means the mixture boils at a temperature below either pure component.

Steam Distillation and Low-Boiling Separation

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synthesis of luminol

Luminol Chemiluminescence in Forensics

Luminol chemiluminescence shows how a chemical reaction can produce light and help with blood detection. Chemical reactions may be endothermic or exothermic, depending on whether they absorb or release heat as reactants become products. The enthalpy of a reaction is the energy difference between reactants and products, or ΔH. A positive ΔH means the reaction is endothermic. A negative ΔH means it is exothermic. Many reactions do not happen in a single step. They can pass through intermediates...

esterification

Ester Formation and Everyday Fragrances

Esters are organic compounds with a carbonyl group attached to an oxygen that connects to another alkyl or aryl group. Their general formula is RCOOR'. They are often made by reacting a carboxylic acid with an alcohol in an esterification reaction. In this process, the hydroxyl group of the acid is replaced by an alkyl or aryl group. Many simple esters have familiar fruit and flower smells because their structures are small and less complex. Formic acid and methanol can combine to form methyl...

identification of unknown aldehydes and ketones

identification-of-unknown-aldehydes-and-ketones

Carbonyl Tests for Aldehydes and Ketones

Aldehydes and ketones are carbonyl compounds, which means they contain a C=O functional group. A ketone has two alkyl or aryl groups attached to the carbonyl carbon. Acetone is the simplest ketone, with two methyl groups. An aldehyde is similar, but it has at least one hydrogen attached to the carbonyl carbon. Formaldehyde is the simplest aldehyde, and acetaldehyde has one hydrogen and one methyl group. The carbonyl carbon in both aldehydes and ketones is electrophilic because the oxygen atom...

uv-vis spectroscopy of dyes

How Dyes Absorb Visible Light

Dyes absorb visible light because their molecular structure lets them interact with specific wavelengths. When light hits a substance, some light is absorbed and the rest is reflected or transmitted. The color we see depends on the wavelength that is reflected. A blue substance reflects blue light, around 430 to 480 nm, and absorbs the complementary orange region, around 590 to 630 nm. Compounds that do not absorb in the visible range appear colorless to the human eye. Light also has energy and...

identifying alcohols

Alcohol Tests for Primary, Secondary, and Tertiary

Alcohol tests can help sort alcohols by structure and reactivity. Alcohols are organic molecules with a hydroxyl group attached to an alkyl or aryl group, written as ROH. If the carbon with the hydroxyl group has one R group, the alcohol is primary. If it has two R groups, it is secondary. If it has three R groups, it is tertiary. Alcohols can also be aromatic when they contain a benzene ring. Phenol is the simplest aromatic alcohol. To identify an alcohol, chemists can use its chemical...

chemistry

Comprehensive, curriculum-focused videos for both instructors and students in introductory chemistry lab courses.

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Learn how steam distillation separates temperature-sensitive organic compounds from water-insoluble mixtures using vapor pressure and low boiling points.

Steam Distillation and Low-Boiling Separation | JoVE K12

استعد لتدريس التقطير بالبخار من خلال هذا الدليل الإرشادي للمدرسين لمدة 4 دقيقة. يغطي خطوات التحضير الأساسية لمختبر Chemistry على JoVE Lab Manual.

تحضير المدرّس لـ التقطير بالبخار في Chemistry - أكثر من 5.6K مشاهدة | JoVE Lab Manual

اتبع إجراءات التقطير بالبخار خطوة بخطوة في فيديو بروتوكول الطالب هذا لمدة 11 دقيقة. جزء من مجموعة Chemistry على JoVE Lab Manual.

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Steam Distillation and Low-Boiling Separation

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