chemical engineering question

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Requirements: Answer the question
CHM 101 ? Separation Using Paper Chromatography
Purpose:
In this experiment you will become familiar with chromatography, a technique used to separate small quantities of mixtures into their component parts. Paper chromatography is used to analyze mixtures of food colors, inks, and amino acids ?
Discussion:
In 1906, Michael Tswett, a Russian botanist, described a method to separate chloroplast from plant tissue into its components. Many of the components were highly colored, and he called the separation technique chromatography (chroma means “color” in Greek) and the visible result of the separation a chromatograph. Chromatography has become increasingly refined and highly varied since that time, and today chromatography is one of the most powerful methods of separation we have.
All forms of chromatography employ a stationary phase and a moving phase. The stationary phase may be very small pieces of clay, porcelain, cellulose, or other material. The moving phase (also called the developing phase) is a solvent or mixture of solvents that flows over the stationary phase. The separation of substances is based on the difference in attraction each has for the stationary phase and for the moving phase.
Types of chromatography:
Column chromatography
Liquid chromatography
Thin layer chromatography
Gas chromatography
Paper chromatography
Paper chromatography is one of the simplest variations on this theme. The stationary phase is paper, very much like filter paper. A small sample of the mixture is spotted? near one end of a strip of paper and dried. The paper is then suspended in a vessel with its lower edge immersed in the developing solvent. As the solvent moves up the paper, the difference between each component’s affinity for the paper and for the solvent affects the separation. In general, paper chromatography is not as effective as the other methods described, but it is inexpensive, fast, and capable of producing good results.
In paper and thin-layer chromatography, the mobility of a substance separated in the analysis is stated in terms of its Rf value. The Rf value equal the ratio of the distance traveled by the substance divided by the distance traveled by the solvent. Each distance is measured from the point at which the mixture is applied to adsorbent, as shown in Figure 1.
The Rf value is the physical property of the substance under the conditions of the analysis. Rf values for the two components separated in Figure 1 are calculated below.
Whether the component spot travels 10 mm or 30 mm from the starting point, the ratio of that distance to the distance traveled by the solvent will remain constant. Also, the same compound under the same conditions will have the same Rf, value each time it is analyzed. This means that Rf values can be used to identify compounds. For example, vitamin C has the same Rf value whether it is part of a mixture of vitamins or is present by itself. If a spot produced from a mixture has the same Rf value as pure vitamin C developed under identical conditions, then vitamin C is in the mixture.
Figure 1. Paper chromatography
Experimental Procedure:
CAUTION: As always, eye protection, gloves, apron must be worn at all times.
In this part of the experiment, you will learn what colors are blended to obtain red, blue, and yellow commercial food colors.
Obtain a 13 x 20 cm piece of chromatography paper from the lab cart. Do not touch the chromatography paper with bare hands. Use gloves and handle the chromatography paper by the edges.
Using a pencil (do not use ink) and a ruler, draw a straight line (line of origin) 1cm from the long edge of the paper. (Figure 2)
Figure 2. Chromatography paper set up
Obtain food coloring samples (3 colors: yellow, red, and blue), one unknown of color mixture, and two different pens. Mark off six points on the line of origin and label each point accordingly with the samples using a pencil. The points should be evenly spaced from one another.
Practice spotting before using the actual chromatography paper: Using a capillary tube, place a small drop of color on a small piece of paper (provided in a beaker on the cart). The spot must not be more than 3 mm in diameter. Otherwise, separation will be difficult. After the practice, spot each of the color samples on the line of origin of the chromatography paper. Let the color samples dry.
Transfer ~20 mL of 1% NaCl solution (eluent) to a 600 mL beaker.
After each sample has been allowed to air dry, bend the chromatography paper into a cylinder without overlapping the edges and staple the ends together about 2 cm from the top and 1.5 cm from the bottom as shown in Figure 3.
Gently lower the paper (spotted end down) into the beaker of eluent and allow the system to develop undisturbed until the solvent front rises to about 2 cm from the top edge of the paper
Figure 3. Stapling of chromatography paper
Immediately remove the paper from the beaker, remove staples, and lay the paper flat on a clean surface. Mark with pencil the exact location of solvent front.
Allow the chromatogram to dry completely. Use a heat gun if needed. If heat gun is used, use the Cold? setting to prevent the burning of the chromatogram.
Measure the distance in millimeters from the line of origin to the dot in the center of each separated component and measure the distance from the line of origin to the solvent front, as shown on the chromatogram in Figure 2. Write these distances in pencil on the chromatogram.
If a particular food color produces only one spot, then it is not a mixture of dyes. Those that produce two or more spots are mixtures. Identify which of the known samples was given to you as an unknown and which color presents in the ink pens. Record your findings on the Report Sheet.
Place used capillary tubes in the broken glass disposal box.
Tape the chromatogram to the Report Sheet. Calculate the Rf value for each food coloring. Calculate the Rf values of the component(s) of your unknown and pens. Show all calculations on the Report Sheet. Use the back side if necessary.
Name: Station #______ Date:
CHM 101 ? Separation using Paper Chromatography
Report Sheet
At the bottom of the page, attach the chromatogram for the paper chromatography experiment you performed.
Food coloring unknown number: ______
Indicate all distances in millimeters on the chromatogram and calculate the Rf value for each component. Show your calculations.
Outline each component found on your chromatogram in pencil. If Rf values are required, indicate those values on the chromatogram. Show all calculations.
Chromatography Data Sheet
Unknown # _____
Food color(s) in unknown mixture: ____________________________________

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