OCHEM Physical Properties 3

OCHEM Physical Properties 3 - Physical Properties:...

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Physical Properties: Determining Melting Points and Boiling Points Lindy Hilpert Brad Hutnik Organic Chemistry 330 September 26, 2007
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Introduction: The purpose of this lab was to find the melting points of crude and pure benzoic acid and to compare them. The other purpose was to determine the boiling point of an unknown liquid and identify it based on this information. To find the melting points, a Mel-Temp apparatus was used, and to find the boiling point, a simple distillation was performed. Reactions, Theories, and Mechanisms: There are two types of properties that a substance can have; intrinsic and extrinsic. Intrinsic properties are dependent on the amount of the substance present and extrinsic properties are not dependent upon the amount of substance present. Physical properties are intrinsic. Physical properties are the properties that are independent upon the quantity of the substance present, but are dependent on the chemical composition. Some physical properties are melting point and boiling point. A melting point is the range of temperatures at which a solid becomes a liquid. A boiling point is the temperature at which a liquid becomes a gas. There are three states of matter; solid, liquid, and gas. A phase change is the transition of any state to another state. The three states can be classified by amount of organization of the matter. A solid is the most organized and is very rigid. A liquid is less organized, and the molecules have some movement. A gas is the least organized. Gases have the highest amount of entropy and are made up of at least 99.9% open space. Different events occur when going from one state to another. When a solid changes to a liquid, it is called melting. This process increases entropy and occurs when the substance gains enough energy to break the attractive forces among its molecules, and usually
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occurs when heat is applied. The temperature at which the solid melts is called the melting point. According to Rogue’s Law, a liquid boils when the partial pressure of the liquid is equal to the partial pressure of the atmosphere. When a liquid turns to a gas, it is called boiling. This process increases entropy. This process also occurs when the substance gains enough energy to overcome the attractive forces among the molecules, and occurs when heat is applied. The temperature at which the liquid boils is called the boiling point. When a gas turns to a liquid, it is called condensing. This process decreases entropy and also occurs when the substance loses energy and can no longer overcome the attractive forces among the molecules. Distillation is used to purify a substance or to separate miscible liquids and identify them based on their boiling points. The process starts with boiling a liquid in a round bottom flask until it begins to evaporate. Then gas then comes in contact with the condenser, which has cool water running through it. The cold causes the gas to condense and flow through a tube into a graduated cylinder. This process allows a very accurate
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This lab report was uploaded on 04/07/2008 for the course CHEM 0330 taught by Professor Forget during the Fall '07 term at Pittsburgh.

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OCHEM Physical Properties 3 - Physical Properties:...

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