Why was sublimation performed under reduced pressure?
Sublimation is a process in which a solid substance directly transitions to a gas without passing through the liquid phase. It is often performed under reduced pressure, also known as vacuum, for several reasons:
1. Temperature control: By reducing the pressure, the boiling point of the substance is lowered, allowing sublimation to occur at lower temperatures. This prevents the substance from decomposing or degrading at higher temperatures.
2. Faster sublimation: The reduced pressure creates a concentration gradient, facilitating the removal of the gas molecules from the solid surface. This speeds up the sublimation process and improves the efficiency of the separation.
3. Improved purity: Sublimation under reduced pressure helps to eliminate impurities present in the solid. Since the gas-phase contaminants are being continuously removed, the resulting sublimed product is often of higher purity compared to other separation methods.
To perform sublimation under reduced pressure, you would typically require a setup involving a vacuum pump and a flask connected to a cold finger or condenser. The solid substance is placed in the flask, and the vacuum pump is started to decrease the pressure inside the system. The cold finger or condenser is cooled to a temperature below the sublimation point of the solid, which aids in the condensation of the sublimed gas molecules. This process allows for the separation and collection of the purified solid product.