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General Chemistry 1100 lab reports...

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Paper Chromatographic Separation of Food Dyes CHEM 1100

Purpose

The aim of this lab is to choose the best solvent between the solutions given which were water, 0.10﹪ NaCl, and 2-propanol. Another aim of this lab was to identify the three unknown from the mixtures of food dyes. Theory/Principles  Chromatography, according to the manual1 is a powerful method used to separate components or

solutes from a mixture, an example is the separation of components from food dye. The stationary phase of paper chromatography is usually the paper being the polar component. The mobile phase of chromatography is the solvent which is less polar than the paper, usually consists of a mixture made from water and a liquid. Microfluidics is the control of fluids by using microchannel technology from a scale that ranges from microliters to picoliters. Microfluidics is being used in chromatography to measure the distance to where the sample and solvent reach during the separation of components from a food dye. The retention factor (Rf) is the ration distance between the solvent and the component sample. Rf can be found by using the following equation: Rf =

distance traveled by solute(sample) ; distance traveled by solvent

Rf < 1

Raw Data Unknowns: Z1, A1, H1 Table 1. The distance of solvents and samples from both pure dyes and unknown dyes using NaCl solvent. Pure Dyes (mm)

Mixture Dyes (mm)

Solvent

Sample

Solvent

Sample

DNaCl: 43 mm

DGreen 3: 37 mm

DNaCl: 43 mm

DA1: 32 mm DA1: 7 mm

DNaCl: 43 mm

DBlue 1: 38 mm

DNaCl: 43 mm

DH1: 38 mm DH1: 9 mm

DNaCl: 43 mm

DBlue 2: 18 mm

DNaCl: 43 mm

DZ1: 32 mm DZ1: 6 mm

DNaCl: 43 mm

DYellow 5: 32 mm

DNaCl: 43 mm

DRed 3: 15 mm

Experimental Found in manual1 Results The unknown were Z1, A1, H1. In order to find out which two food dyes made up the mixtures for the unknown, observation is key to finding what colors the mixtures of unknown are made out of. Z1: Yellow5 + Red3 A1: Blue1 + Red3 H1: Blue1 + Red3 Table 2. Retention factor values for five pure dyes and the three unknown mixture dyes Pure Dyes (mm)

Mixture Dyes (mm)

Rf values

Rf values

DGreen 3: 0.860 mm

Dyellow 5: 0.744 mm DRed 3: 0.163 mm

DBlue 1: 0.884 mm

DBlue 1: 0.884 mm DRed 3: 0.209 mm

DBlue 2: 0.419 mm

DBlue 1: 0.774 mm DRed 3: 0.140 mm

DYellow 5: 0.774 mm DRed 3: 0.349 mm

Sample Calculation: Rf =

distance traveled by solute(sample) distance traveled by solvent

=

DGreen 3 : 37 mm DNaCl : 43 mm

= 0 .860 mm

Discussion Questions: 1. Count the number of ionic sites and polar bonds, such as -OH for each dye. Is there a correlation between the number of sites and polar bonds and the Rf value (or how high the dye travels up the paper)? The correlation between polar bonds and the retention factor value is with the higher the retention factor value the more nonpolar the compound is and the faster it will go up the polar paper; on the other hand, the lower the retention factor value is the slower it will go up or not at all, making it a polar compound 2. Suggest a solvent system that might improve the separation of the dyes. Explain your choice (intermolecular forces might prove helpful). A solvent system that might improve the separation of the dyes would be mixing two different solvents in order to use both their properties to separate the dyes better, one of them can be polar and another can be nonpolar. This will help if there are any nonpolar and polar samples.

3. A. What solvent system would be best for washing b1 out from a cotton shirt(cotton is structurally similar to paper) The solvent system that would be best for washing b1 out from a cotton shirt would be using water or sodium chloride as the solvent since cotton is structurally similar to paper. Looking at food coloring in the paper chromatography the b1 food color traveled further and separated the pigment more efficiently with sodium chloride than with water and 2-propanol. B. What solvent system would be best for g3? The solvent system that would be best for g3 would be sodium chloride as well for the same reason b1, g3 moved more using sodium chloride so it will be more efficient. 4. Why must (a) beaker containing the mobile phase and stationary phase be covered and (b) the spots of the samples be above the level of the mobile phase? (a) The beaker containing the mobile phase and stationary phase must be covered to prevent the solvent from evaporating before the completion of the chromatography and can intervene with how the solute moves within the solvent system. (b) If the spot of the samples is placed above the solvent, it will prevent them from being dissolved and from traveling up the paper chromatography. 5. Calculate the uncertainties in the Rf, values of your known dyes. What statistical test  could you apply to give some quantitation of your confidence that your known and unknown have the same Rf values?

6. In the solvent system that you used for analyzing your unknown (a) name the important intermolecular forces acting between the dye and the solvent and (b) dye and the stationary phase for (i) the dye with the largest Rf values and (ii) the dye with the smallest Rf value. Comment on the relative importance of the types of forces that result in the  observed Rf values.  (a) The important intermolecular forces acting between the dye and solvent was ion-ion forces for the solvent and dye. (b) The important intermolecular forces acting between paper and dye was a ion-dipole force. (i) The two dyes with the largest retention factor values were blue1 and green with values of 0.860 mm and 0.884 mm, meaning that they were able to separate better and traveled up the paper more. (ii) The dye with the smallest retention factor value was red3 with a value at 0.349 mm, the slower it will travel or not at all.

Reference

1. Goldwhite, H., Tikkanen, W., Kubo-Anderson, V., & Mathias, E. (n.d.). Experiments in General Chemistry ( 5th ed.). Macmillan Learning, 2018. p. 69-76

Figure 1. Chromatography paper using three different types of solvents and five pure dyes....