Many common materials are composed of mixture of compounds. Separating mixtures

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Many common materials are composed of mixture of compounds. Separating mixtures to determine the identity of one or more compounds has many practical applications in the fields of medicine, law enforcement, environmental studies, and in manufacturing. It is often difficult to separate mixtures if the compounds are chemically similar. Chromatography is a technique used to identify and analyze components of a mixture The word chromatography is derived from two Greek words meaning color (chroma) and writing (graphein) color writing." The term was coined by the Russian chemist Mikhail Tswett (1872-1919) in 1903 to describe a new technique he had invented to separate the pigments in green plant leaves. Tswett found that in addition to the main green pigment, chlorophyll, plant leaves also contain red and yellow secondary pigments. The results were literally "written in color" when a plant extract was passed through a column containing a clay-like absorbent solid. Although there are several types of modern chromatographic methods available, all chromatography relies on the same principles two or more compounds are "partitioned" on the basis of their relative distribution between two phases, one phase is stationary and the other is mobile. In other words, substances are separated on their relative affinities for the stationary phase and or mobile phase Pap romatography is a type of chromatography called 'adsorption chromatography'. The paper is the stationary phase and acts as an adsorbent, a solid that is capable of attracting and binding with the components in a mixture (think of the word adhere). The sample mixture to be separated i spotted" onto the surface of the paper, and a solvent the mobile phase is then allowed to seep through the paper by capillary action. As the components of the mixture dissolve in the solvent, they will travel up the paper at different rates depending on their characteristic physical properties, such as solubility. If one of the components in the mixture is more strongly adsorbed onto the paper than another, it will spend less time in solution and will move up the paper more slowly than the solvent. Components that are not strongly adsorbed onto the paper will spend more time in solution and will more up the paper at a faster rate. This partitioning of the components of a mixture between the paper and the solvent separates the components and gives rise to different bands, depending on their physical attraction for the paper versus the solvent. If the components of the mixture are colored, the bands are easy to see Radial chromatography is a technique using a paper circle with a hole in the center. Ink is potted onto the circle. A paper "wick" is inserted into the hole and then placed in a cup of water, making sure the paper circle does not come in direct contact with the water (Figure 1). The water see up the wick, then outward through the paper. The different pigments making up the ink mixtures will separate in a circular (radial pattern. The resulting pattern is called a chromatogram Filter Paper Ink Cone- Hole O Dots Plastic Shaped Cup Wick Water Ink Line Wedge- Shaped Paper Figure 1. Radial Paper Chromatography

Explanation / Answer

2. The paper is the stationary phase and acts as an adsorbent. Hence, If a sample is stronly adsorbed to the paper, it will have high affinity to the stationary phase.

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