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Determination of Melting Point of Acetylsalicylic Acid by Capillary Method (CAT#: STEM-PPA-0040-YJL)

Introduction

Acetylsalicylic acid, also known as aspirin, is an analgesic-antipyretic medicine made by salicylic acid interacting with acetic anhydride. It is a white crystalline powder, odorless, stable in dry air. It will be slowly hydrolyzed to be salicylic acid and acetic acid in moist air, and aqueous solution has acidic reaction. Slightly soluble in water, soluble in ethanol, ethyl ether, chloroform, sodium hydroxide solution and sodium carbonate solution.




Principle

Melting point is a characteristic property of solid crystalline substance. It is the temperature at which the solid phase changes to the liquid phase. This phenomenon occurs when the substance is heated.
The melting point measurement is usually performed in thin glass capillary tubes with an internal diameter of 1 mm and a wall thickness of 0.1 – 0.2 mm. A finely-ground sample is placed in the capillary tube to a filling level of 2 – 3 mm and introduced in a heated stand (liquid bath or metal block) in close proximity to a high accuracy thermometer. The temperature in the heating stand is ramped at a user-programmable fixed rate. The melting process is visually inspected to determine the melting point of the sample.

Applications

Chemical industry; Cosmetic/pharmaceutical industry

Procedure

1. Seal capillary.
2. Fill the sample.
3. Install the instrument.
4. Determine the melting point.

Materials

• Sample Type: crystalline compounds