Question

Why didn't we use ethanol instead of dichloromethane to extract caffeine from the energy drink?

Sublimation can be an excellent technique for purifying a compound with which of the following specific characteristics?

A High vapor pressure at a temperature above its melting point

B High vapor pressure at a temperature below its melting point

C Low vapor pressure at a temperature above its melting point

D Low vapor pressure at a temperature below its melting point

How is it possible to obtain the melting point of caffeine if it sublimes upon heating?

A Its impossible because it cannot ever be in the liquid phase

B By using a sealed capillary tube the compound cannot escape as a gas

C By not using vacuum, which promotes sublimation, during the melting point determination

D Both B and C are correct

Answer 1

• Caffeine is properly soluble in dichloromethane and moderately in ethanol. Ethanol being polar solvent, many water soluble components can be soluble in it. So extraction of caffeine also leads to the extraction of such components. As a result, separation is not perfectly done because there are some impurities remain within the desirable extracted product. These problem can be overcome by using non polar solvent such that dichloromethane, in which only caffain is dissolved and get the desirable product.
• Option A ) High vapour pressure at the temparature above the melting point. Sublimation is occurring in those compounds which are highly volatile hence have high vapour pressure. According to the phase diagram, if pressure is above the Tripple point temparature, then on increasing temparature the solid directly converted to vapour (skip to the melt).
• Option A