Summary
Highlights
During heating, the Naphthalene in the capillary tube is observed. The temperature at which it begins to melt is recorded from the thermometer. The video explains that if the observed melting point (e.g., 79.6°C) is slightly lower than the known fixed melting point (80°C), it indicates the substance is not entirely pure. Therefore, determining the melting point is a method to check the purity of a substance.
This video introduces Experiment Number 9, which focuses on determining the melting point of Naphthalene. Naphthalene is described as a simple organic compound, a white crystalline solid with the chemical formula C10H8, and insoluble in water. The video highlights that this experiment is important for short-answer questions due to its straightforward nature.
The video defines melting point as the temperature at which a solid substance transitions into a liquid state under standard atmospheric pressure (1 ATM). It emphasizes that this is a fixed point for pure substances. For Naphthalene, the fixed melting point is 80°C. The video also explains that changing atmospheric pressure can affect the melting point.
The necessary materials for the experiment include: powdered Naphthalene, a capillary tube (or test tube), a thermometer, a beaker, water, a wire gauze, and a burner. The importance of using powdered Naphthalene is highlighted.
The step-by-step experimental setup involves binding a capillary tube containing powdered Naphthalene to a thermometer. This assembly is then suspended in a beaker filled with water, which is placed on a wire gauze over a burner. The water is then heated slowly. Crucially, the capillary tube and thermometer must not touch the bottom or sides of the beaker.
Common viva questions are addressed, including the definition of melting point, Naphthalene's melting point (80°C), and the advantage of determining melting point (checking purity). The chemical formula (C10H8) and physical properties of Naphthalene are detailed: it's a white crystalline solid, insoluble in water, has a melting point of 80°C, a boiling point of 218°C, is soluble in non-polar solvents like benzene, and undergoes sublimation (direct conversion from solid to gas).