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Recrystallization and Melting Point

Sabrina Liao

Simpson University


The purpose of the experiment is to purify compounds by dissolving impurities in a solvent.



100ml of water was placed inside a 250ml Erlynmayer flask and 10 ml was added into the 100 ml beaker containing the unknown substance after scraping the unknown substance off the sides and bottom of the beaker. Then, two boiling stones were placed inside both the flask and the beaker in order to prevent intense reagent splattering. After that, the erylenmyer flask and the beaker were both placed on the hot plate at 215 degrees. After around 13 minutes, around 3ml of water from the flask containing the hot water was transferred into the beaker that included the unknown to dissolve the remaining undissolved substance floating inside the beaker. Since there were still some undissolved substance, filter paper, and a new beaker was used to filter the substance out. After that, the beaker and the flask were both placed inside the ice bath for 7 minutes. Next, a piece of paper was placed inside the Buchner funnel and it was wet with distilled water. Then, the beaker and flask were removed from the ice bath, and the unknown substance was scooped out of the beaker by a stir stick and put inside the Buchner funnel. The funnel was connected to the vacuum. The vacuum was run for 5 minutes and 30 seconds. The remaining substance inside the beaker was rinsed by the ice water that was ice-bathed before.

Identification of the unknown:

Placetin was obtained by a capillary tube that is sealed on one side. After that, a long glass tube was used to make the substance go to the bottom of the capillary tube. The unknown substance and acetanilide were also obtained using the same method. After obtaining the phenacetin inside a capillary tube, the capillary tube with the phenacetin was placed inside the melting point apparatus, and the expected temperature was set to 135 degrees Celsius. The probe was connected to the melting point apparatus in order to measure the melting point of the substances. The melting point was recorded when the phenacetin was first melted and when it finished melting. The melting points of unknown and acetanilide were examined using the same method.

Results and statistics

  • Crude mass of unknown = 0.761g

  • Mass of unknown after crystallization = 0.550g

  • Percent recovery= 0.550g/0.761g= 72.3%

  • The melting point of unknown: 108.8 degrees celsius~110.9 degrees Celsius

  • The melting point of phenacetin (measured): 135.4 degrees Celsius ~ 136.8 degree Celsius

  • The melting point of acetanilide (measured): 115 degrees Celsius ~ 116.8 degrees Celsius

  • The melting point of phenacetin (literature): 135 degree Celsius

  • The melting point of acetanilide (literature): 115 degree celsius

  • The unknown identity is acetanilide, for it has the same melting point as the acetanilide.


To figure out the identification of the unknown substance, the unknown substance was purified by recrystallization followed by its melting point being measured using a melting point apparatus. The melting points of known products, acetanilide, and phenacetin, were also examined and compared with the melting point of the unknown substance to find out the identification of the unknown substance. In the experiment, the melting point of the unknown substance was 135 degrees celsius which is the same as the measured melting point of acetanilide. Therefore, the result of the experiment is that the unknown substance is acetanilide.


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