Question

give one advantage and one disadvantage of using 9.0 of alumina in your column instead of 4.5 g as you did during the column chromatography experiment in lab.

Answer 1

Silica gel (SiO₂) and alumina (Al₂O₃) are two adsorbents commonly used by the organic chemist for column chromatography.

Alumina is used more frequently in column chromatography than it is in TLC. Alumina is quite sensitive to the amount of water which is bound to it: the higher its water content, the less polar sites it has to bind organic compounds, and thus the less "sticky" it is. This stickiness or activity is designated as I, II, or III, with I being the most active. Alumina can be activated by heating at 300°C. Alumina is usually purchased as activity I and deactivated with water before use according to specific procedures. Alumina comes in three forms: acidic, neutral, and basic. The neutral form of activity II or III, 150 mesh, is most commonly employed.

According to the question advantage of 9 g of alumina instead 4.5 g in column. i.e., quantity effect on column. Then,

Advantage: Adsorption capacity of alumina is more and compounds can be resolved in column more effeciently.

Disadvantage: Takes more time for separating the mixture. Alumina catches moisture by time thus its resolution capacity will decrease.