Separation of the Components of a Mixture Purpose: To become familiar with the methods of separating substances from one another using decantation, extraction, and sublimation techniques. Apparatis and Chemicals: balance, Bunsen burner, rubber hose, tongs, 2 evaporating dishes, 2 watch glasses, 100-mL graduated cylinder, clay triangles, 2 ring stands, 2 iron rings, 2 glass stirring rods, unknown mixture of NaCl, NH4Cl, SiO2. Discussion: Mixtures are composed of two or more substances mixed together. Mixtures can be homogeneous, or uniformly distributed; they can also be heterogeneous, or not uniformly distributed.
The components of a mixture remain chemically unchanged. They are merely physically mixed. Therefore, it is possible to separate them. There are several ways to separate substances, depending on the properties of the substances. Some substances dissolve when placed in water. These substances are soluble in water. Others are unchanged when placed in water. These substances are insoluble in water. Thus, if a soluble substance is mixed with an insoluble substance, separation through decantation can take place.
Decantation involves pouring water onto a mixture and stirring.
The soluble substance will dissolve, leaving the insoluble one intact. The newly-formed aqueous mixture of water and the soluble substance can be poured into a separate container and heated so that the water evaporates. The substance have now been separated without any changes to the elemental composition of the substances. Decantation is usually performed more than once on the insoluble substance to ensure that all particles of the soluble substance have been removed. Some substances can pass directly from the solid to the gaseous stage without first melting and becoming liquid.
These substances are said to be able to sublime. Substances that sublime, when mixed with substances that do not sublime, can be separated by heating the mixture until the substance that can sublime is completely gone. Another method of separation is called filtration. This is the process of separating a solid from a liquid by means of a porous filter which allows the liquid to pass through but not the solid. This has nothing to do with solubility or ability to sublime, but rather simply the physical phase of the substances and the permeability of the filter.
Extraction is the separation of a substance from a mixture by preferentially dissolving that substance in a suitable solvent. By this process a soluble compound is usually separated from an insoluable compound. All ionic compounds are soluble in water. In this experiment, three pre-mixed substances will be separated using the procedural methods given. These substances will be separated as follows: NaCl (extraction with water), NH4Cl (sublimation), and SiO2 (evaporation). Results were recorded. Observations: The percent recovery for this experiment was low.
There were sources of error that affected the amount of substance that could be recovered. During heating, some of the silicon dioxide spattered onto the watch glass. After heating was complete, in an attempt to keep the amount of silicon dioxide consistent, the silicon dioxide on the watch glass was swept into the evaporating dish. However, not all of the substance fell into the evaporating glass. The substance that fell onto the tabletop was not recoverable. Another source of error is the decanting process.
Since this process is subject to human error at every point, it is likely that an error occurred during the process, such as pouring excess water from the original dish into the receptacle dish, causing some of the substance in the first dish to enter the second, or dropping sample in evaporating dish on the floor and shattering it altogether. However, this is not necessarily a source of discrepancy in masses, as decanting is a separating process. Separation processes do not affect total mass, but rather individual masses.
The individual masses could have been changed by errors in decanting, but not the overall mass. Post -Laboratory Questions 1. It cannot be done in a different order while still measuring mass. Ammonium chloride is very soluble in water. If the entire original sample was put in water, only the silicon dioxide would be left behind after decantation. Then, when heating the mixture of water, sodium chloride, and ammonium chloride, three things would be happening at once: the evaporation of water, the precipitation of sodium chloride, and the evaporation of aqueous ammonium chloride.
Thus, the mass of the ammonium chloride could never be determined. Only the mass of sodium chloride and silicon dioxide could be determined. 2. BaSO4 has a very low solubility in water. NH4Cl has a very high solubility in water. Thus, the mixture could be put in water and decanted. This would separate the two substances. 3. BaCl2 is very soluble in water but CaSO4 is not. So add water. Then filtrated to get the BaSO4. Evaporate the solution and you get back BaCl2. 4. Just add water. The potassium bromide will go into solution, the naphthalene will not. Filter off the naphthalene.
Allow the water in the potassium solution to evaporate, and you have now separated the naphthalene and the potassim bromide. Or simply put both into an evaporating dish and heat strongly until allof the naphthalene has sublimed. What remains in the dish will be potassium bromide. 5. Dissolve the mixture in an organic solvent such as ether. Put in a sep funnel. Wash the solution with aqueous sodium hydroxide. This will convert the napthol to its sodium salt which will be water soluble. Only the benzophenone with be left in the ether layer.
To reclaim the naphthol, acidify the water layer which will convert the water soluble naphthol sodium salt back to naphthol, which is ether soluble. Shake the acidified water layer with fresh ether. You will now have two ether solutions, each containing one of the original components. Evaporate the ether. Conclusion: The experiment was completed to a high degree of success. Familiarity with the methods of separating substances from one another using decantation, extraction, and sublimation techniques was gained, and the material was recovered to a reasonable degree of accuracy.
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