Though chromatography is a simple technique in principle, it remains the most important method for the separation of mixtures into its components. It is quite versatile for it can be used to separate mixtures of solids, or of liquids, or mixtures of solids and liquids combined, or in the case of gas chromatography, can separate mixtures of gases.
The two elements of chromatography are the stationary phase and the mobile phase. There are many choices of stationary phases, some being alumina, silica, and even paper. The mobile phase, in liquid chromatography, can also vary. It is often either a solvent or a mixture of solvents and is often referred to as the eluant..
A careful choice of eluting solvent helps to make the separation more successful. The mixture is placed on the stationary phase. The eluant passes over the mixture and continues to pass through the stationary phase carrying along the components of the mixture. If a component in the mixture has greater affinity for the mobile phase eluant than the stationary phase, it will tend to be carried along easily with the eluant.
If another component in the mixture has a greater affinity for the stationary phase than the mobile phase then it will not be carried along so easily.
A separation is thus obtained when the different components in a mixture have different affinity for the stationary and mobile phase. Three important types of chromatography based on the principles discussed above are: 1 thin layer chromatography TLC , 2 column chromatography, and 3 gas chromatography.
What method of separation would be most effective on the following mixtures:. Mixtures can be physically separated by using methods that use differences in physical properties to separate the components of the mixture, such as evaporation, distillation, filtration and chromatography. The process typically involves heating the mixture until no more liquid remains, Prior to using this method, the mixture should only contain one liquid component, unless it is not important to isolate the liquid components.
This is because all liquid components will evaporate over time. This method is suitable to separate a soluble solid from a liquid. In many parts of the world, table salt is obtained from the evaporation of sea water. The heat for the process comes from the sun.
Once the sea water in these evaporation ponds has evaporated, the salt can be harvested. Filtration is a separation method used to separate out pure substances in mixtures comprised of particles some of which are large enough in size to be captured with a porous material. Particle size can vary considerably, given the type of mixture. For instance, stream water is a mixture that contains naturally occurring biological organisms like bacteria, viruses, and protozoans.
Some water filters can filter out bacteria, the length of which is on the order of 1 micron. Other mixtures, like soil, have relatively large particle sizes, which can be filtered through something like a coffee filter. Use this resource to answer the following questions:.
Skip to main content. Matter and Change. Search for:. How did goldminers search for gold? Figure 2. Typically, chromatography is performed by placing a mixture of two or more chemicals into a glass column filled with silica. When an organic solvent such as ethyl acetate or alcohol is poured through the column, one of the components of the mixture will tend to stick to the silica better than the other. As a result, the less sticky one will pass through the column more quickly, while the stickier one will take a little longer.
Let's say that you have a compound dissolved in a liquid that you want to remove. For example, you have a small amount of salt dissolved in oil and want to remove it. How would you do this? Though distillation could do the job, it takes a long time and considerable effort.
An alternate way of making this separation is to find a liquid that isn't soluble with the first liquid and that's better at dissolving the salt than the oil is. When the two liquids are mixed and shaken, the salt will tend to move from the oil where it's not very soluble into the water where it is. When this process is complete, it's a simple matter to pour out the water, leaving behind the pure oil. All rights reserved including the right of reproduction in whole or in part in any form.
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