Determining the boiling point of organic compounds is essential for understanding their properties and behavior. It is the temperature at which a substance changes its state from liquid to gas. Several factors contribute to the boiling point of organic compounds, including intermolecular forces, molecular weight, and symmetry. In this article, we look into what a boiling point is, organic compounds, how to determine the boiling point of a given compound, precautions, etc.
What is Boiling point?
Boiling point is the temperature at which the vapor pressure of a liquid is equal to the external pressure surrounding the liquid. It is the temperature at which the substance changes state from a liquid state to a gas state.
The boiling point of a liquid varies depending on the surrounding atmospheric pressure. For example, water boils at 100°C (212°F) at sea level but at a lower temperature at higher altitudes. The boiling point is a characteristic physical property of a substance and is used to identify and characterize different compounds.
Methods to Determine Boiling Point of Organic Compounds
Boiling point of a substance can be determined using various methods, including Distillation, Reflux, Thiele tube method, Gas Chromatography, and the capillary method. The most common methods used for the determination of the boiling point of organic compounds are:
- Simple Distillation Method
- Gas Chromatography
- Differential Scanning Calorimetry
Simple Distillation Method
Boiling point of a substance can be determined using the simple distillation method. This method involves heating the sample in a distilling flask and recording the highest temperature at which the vapor pressure of the liquid equals the external pressure, which is the boiling point. It is essential to use at least 5 mL of the sample in the distilling flask.
Recording the barometric pressure along with the boiling point is also recommended to ensure accuracy. The distillation method is commonly used for identifying and purifying organic compounds, as the boiling point is a well-defined physical property that can aid in compound characterization.
Gas Chromatography
Gas chromatography (GC) is a technique that separates and analyses compounds in a mixture. It involves injecting a gaseous or liquid sample into a mobile phase, typically a carrier gas, and passing it through a stationary phase. The sample components are separated based on their interactions with the stationary phase. Gas Chromatography is widely used in various fields, including analytical chemistry, forensic science, environmental analysis, etc.
Gas chromatography is particularly well-suited for analyzing volatile organic compounds. It requires frequent calibration and is sensitive to environmental factors such as water vapor and strong electrical fields.
Differential Scanning Calorimetry
Differential Scanning Calorimetry (DSC) is a thermo-analytical technique used to measure the temperature and heat flow associated with phase transitions in materials. It is a powerful tool for gauging the stability of proteins or other biomolecules in their natural state.
DSC is also utilized in biology and nanoscience for measuring the thermal properties of biomolecules and nano-sized materials. In simple terms, DSC measures the heat absorbed or released by a sample as it is heated or cooled, providing valuable information about the sample’s characteristics and behavior.
Step-by-Step Procedure for Boiling Point Determination
Aim: To determine the boiling point of benzene.
Apparatus: An organic compound, a capillary tube, a thermometer, a kerosene burner, and a fusion tube.
Set up of Experiment: The set up of experiment is shown below:
Experimental Setup for Determination of Boiling Point
Preparation and Setup
- Close one end of a capillary tube by holding it in a flame and rotating it for 2-3 minutes.
- Transfer a few milliliters of benzene to a fusion tube.
- Immerse the capillary tube into the liquid in the fusion tube, keeping the seal end up.
- Insert the tube in the holes of an aluminum block and a thermometer in the other hole.
- Ensure that the Benzyldehyde liquid is visible in the fusion tube.
- Heat the container gently over a Kerosene burner or other heat source.
- Observe the temperature using the thermometer and record the temperatures t1 and t2.
- Boiling point of benzene can be calculated as the average of t1 and t2.
Observation and Result
Temperature observation of benzene is as follow:
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Temperature ( t1)
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77°C
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Temperature (t2)
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79°C
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Boiling point of benzene (t1+t2)/2
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78°C
|
Calculation
Mean of temperatures taken from the experiment:
Boiling point = (t1 + t2)/2 = (77+79)/2 = 78°C
Boiling point of benzene is found to be 78°C.
Common Error
- Recording a temperature before hot vapors fully immerse the thermometer bulb is a common source of error in boiling point determination.
- Measurement uncertainty, including random and systematic errors, can affect the accuracy of reported boiling points.
Factors Affecting Boiling Point
Many factors that affect the determination of boiling point include:
- Molecular structure and Intermolecular forces
- Impurities and Solvent effect
Molecular Structure and Intermolecular Forces
Molecular Structure influence the boiling point of a sample. Larger molecules tend to have higher boiling points compared to smaller molecules. This is because larger molecules have stronger London dispersion forces between their atoms, which require more energy to overcome during boiling.
Boiling point of a solvent is also affected by factors such as the intermolecular forces present in the molecules. The stronger the intermolecular forces, the lower the vapor pressure of the substance and the higher the boiling point.
Impurities and Solvent Effect
Impurities generally lower the melting point of a compound but raise the boiling point. This is because the impurities decrease the vapor pressure of the solvent, leading to an increase in the boiling point.
Solvent can also alter the boiling point of a sample. Solvents with high boiling points may require higher temperatures for efficient boiling, while volatile solvents may evaporate prematurely.
Application of Boiling Point
Some applications of boiling point are given below,
- Identification of Compounds: The boiling point of a compound is a physical constant, similar to the melting point, and can be used to support the identification of a compound.
- Separation Techniques: Boiling points are utilized in separation techniques such as distillation, fractional distillation, and steam distillation.
- Purity Analysis of Organic Compounds: The purity of an organic compound can be determined using boiling point of the compound.
- Material Science: Boiling points are relevant in material science for understanding the thermal properties of materials, such as polymers, metals, and ceramics.
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Viva Questions on Boiling Point
Some viva questions on Boiling Point of Organic Compound are,
Define Organic Compound.
Organic compounds are defined as chemical compounds which contain carbon atoms linked with other elements through simple covalent bonds. These elements could be connected by single covalent bonds, double covalent bonds, or triple covalent bonds.
What is Boiling Point of Benzaldehyde?
Boiling point of benzaldehyde is about 178 °C.
What is Effect on Boiling Point when Pressure is Increased?
Boiling point of a liquid increases with an increase in outside pressure.
What is Boiling Point of Water?
Boiling point of water is 100 °C.
What is Boiling Point of Nitrobenzene?
Boiling point of nitrobenzene is around 210 °C.
Boiling Point of Organic Compounds: FAQs
What Determines Boiling Point of Organic Compound?
Boiling point of an organic compound is determined by several factors, including:
- Intermolecular Forces
- Molecular Structure
- Polarity
- Hydrogen Bonding
- External Pressure
What is Significance of Boiling Point in Organic Chemistry?
Boiling point in organic chemistry reflects a compound’s tendency to vaporize. It helps determine purification of a compound and also determine its physical properties. Boiling points aid in identifying and characterizing organic compounds, playing a crucial role in various laboratory and industrial processes.
How Does Molecular Structure Affect Boiling Point?
Boiling point is influenced by molecular structure in terms of intermolecular forces. Molecules with stronger forces, like hydrogen bonding, generally have higher boiling points. Larger and more complex molecules may also exhibit elevated boiling points due to increased surface area and stronger interactions.
What are Limitations of Traditional Boiling Point Determination Methods?
Traditional boiling point determination methods may be limited by impurities affecting readings. Atmospheric pressure variations can impact results, and some compounds may decompose before reaching their actual boiling point.
Can Boiling Point Determination Help in Identifying Unknown Compounds?
Yes, boiling point determination is a valuable tool for identifying unknown compounds. It provides a distinctive characteristic, aiding in comparison with the known data.
How Accurate are Boiling Point Determination Methods?
Boiling point determination methods are generally accurate, but variations can occur due to impurities or atmospheric pressure changes. Modern techniques, like advanced instrumentation, enhance precision compared to traditional methods.
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