Fractional Crystallization General Chemistry 101/102 Laboratory Manual University of North Carolina at Wilmington

Fractional Crystallization Purpose Use the technique of vacuum filtration to separate a heterogeneous mixture into its components. Use the technique of fractional crystallization to separate a homogeneous mixture into its components. Safety Considerations Exercise care not to burn yourself on hot ringstands, rings, and beakers. Dispose of all waste materials in the appropriately labeled containers in the hood.

Fractional Crystallization Procedure Add about 25 g of one of the unknown mixtures to a pre-weighed 250 mL beaker. Weigh the beaker and mixture to determine the mass of the mixture. Add 60 mL of DI water to the beaker and heat the mixture to 85 ºC (do not allow it to boil) while stirring. Keep the mixture near 85 ºC for 5 minutes with stirring. While the mixture is heating, setup a vacuum filtration system.

Fractional Crystallization Procedure Place a piece of filter paper in the Büchner funnel with the curved edge down. Moisten the paper with a small amount of DI water. curved edge down Turn on the water to the aspirator and pour the hot solution into the funnel. Use the rubber policeman to transfer all solid material to the funnel. sand filtrate

Fractional Crystallization Procedure Pour the filtrate into a clean 250 mL beaker and save it for the recrystallization. While applying suction, wash the sand twice with 25 mL portions of DI water. Continue to apply suction for 3-4 minutes to help dry the sand. Discard the wash water that collects in the flask. Transfer the sand and filter paper to a pre-weighed watch glass and allow the sand to finish drying.

Fractional Crystallization Procedure Heat the solution in the 250 mL beaker to boiling. Allow it to boil for about 3 minutes to reduce the volume of water in the solution. Cool the solution to room temperature by placing the 250 mL beaker into a 600 mL beaker containing 100 mL of tap water. Cool the solution further by placing ice in the 600 mL beaker.

Fractional Crystallization Procedure Turn on the aspirator and pour the mixture containing the borax crystals onto the Büchner funnel. Wash the borax crystals with a 10 mL portion of ice water. Continue the suction for 3-4 minutes to help dry the crystals. Transfer the borax crystals and filter paper to a pre-weighed watch glass. Determine the mass of the borax crystals.

Fermentation and Distillation Procedure While waiting for the borax to finish crystallizing, construct the fermentation system shown below for the Fermentation and Distillation experiment.