Question

My son loves to drink carbonated water from his soda stream machine. Draw the Log C vs. pH diagram for this open system and then calculate the equilibrium pH in the water if the soda stream machine provides a CO2 rich atmosphere with pco2=10atm. You may disregard equilibrium with the co32- species.

Answer 1

The purpose of this experiment was to determine the yield, percent recovery and melting point of caffeine isolated from tea bag. During the experiment, a tea bag was heated in boiling water for about 15 minutes. The resulting mixture was collected for the extraction of caffeine. Caffeine isolation was accomplished from the mixture using methylene chloride. This is because caffeine is more soluble in methylene chloride than in water. Sodium carbonate was also added to the mixture. This was done to form a sodium salt derivative of tannin compounds contained in tea. Tannins are a class of compounds that have certain properties in common.1

Tannins have a phenolic group and also hydrolyzes to form an acid. Because of their phenolic groups and acid formation after hydrolysis, they can react with sodium carbonate to form a salt. The salt is soluble in aqueous solution; therefore, it does not separate into the organic layer. The organic layer separates to the bottom because methylene chloride is denser than water. A micro pipet was used to transfer the organic layer to a flask. It was dried using sodium sulfate. The resulting dry mixture was evaporated by heating. Because of low boiling of methylene chloride, it vaporizes at 400C and impure caffeine crystals were collected. Caffeine do not vaporizes at this temperature because it has a boiling point of 1780C and a melting point of 2380C. The impure caffeine had a melting point range of 223.6-229.30C. This suggested that it contained impurity. Sublimation was used to extract pure caffeine from the impure. The tea bag yielded 0.031g of crude caffeine, which is about 1.3% of the mass of tea in one tea bag. 13% of pure caffeine was recovered after sublimation. The sublimed caffeine had a melting point range of 231.2-234.60C.