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Experiment 3

By April Wells,2014-07-05 04:11
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Experiment 3Expe

Experiment 1 Chemistry 51

    Analysis of Matter using Scientific Method

    INTRODUCTION:

     In the last laboratory experiment you were introduced to Archimedes, Demokritos, and Scientific Method. In this lab, you will use Scientific method to determine the composition of some materials. Matter can be separated into two categories: mixtures and substances. Mixtures are composed of two or more substances and can be separated by physical methods. There are two types of mixtures, homogeneous mixtures of uniform composition and heterogeneous mixtures, which are composed of two or more phases or components. Substances can be described as either compounds or elements. Compounds are substances that can be separated by using chemical methods. Elements can not be broken down into simpler substances. Elements are the building blocks of matter.

     The purpose of this experiment is to analyze household items as either a mixture (heterogeneous or homogeneous) or a substance (compound or element) using both physical and chemical methods, then you will test your power of deduction by analyzing unknowns samples.

Section 1: Scientific Method using Paper Chromatography Time: 30 min set-up/ 30 min wait

    Section 2: Scientific Method on Household Items. Time: 1 hour

Section 1: Scientific Method using Paper Chromatography

INTRODUCTION

    Commercial Food Dyes are mixtures composed of individual compounds. If you read the label for the ingredients for a commercial food dye you would probably find terms like FD&C Yellow 5 or just simply BLUE 1 or RED 40. The purpose of this experiment is to separate the dye mixture into its respective compounds (or components) and observe the effect solubility (eventually we will be able to describe these difference in terms of bonding forces) has on compounds. Chromatography is a method of separating the components or compounds of a mixture by distributing them between two phases; in general a moving phase passing a stationary phase. The moving phase in this experiment is the solvent (a 0.1 % sodium chloride solution) and the stationary phase is the cellulose of the chromatography paper. The attraction the mixture components have to either the moving phase or stationary phase depends on the properties of that specific compound. Particles of similar property will be more attracted to each other than particles that are intrinsically different from each other. In paper chromatography the particles whose properties are most similar to the solvent particles will move up the stationary phase by capillary action along with the solvent. The height to which the components of the mixture rise depends upon the relative strength of the mixture particles to the moving phase as well as the relative strength of the mixture particles to the stationary phase. If the mixture particles are attracted to the stationary phase particles then there will be little movement. Since the different components of the mixture are not attracted to the paper and to the solvent to the same degree, these compounds (components) will move with different speeds along the paper and thus be separated.

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     In this section you will observe the effect chromatography has on four different dye mixtures (yellow blue, red, and green) from McCormick, Shilling, or a generic brand. You will want to deduce the extent of relative attraction each component or compound of the food dye has to both the moving phase and stationary phase. Each lab partner will analyze a different manufacturer enabling you to compare the dye composition of an expensive brand name dye with that of the cheap generic dye. Lastly, you will analyze an unknown mixture composed of two or more of the dye mixtures.

Preparation of the filter paper:

     Prepare the pre-cut chromatography paper (11 cm x 20 cm) by drawing a pencil line 1.5 cm from one edge and another line exactly 8.0 cm above the first. The lower line is your baseline and the upper line is your ending point (for the moving phase). Place five evenly spaced pencil "X" marks along the lower line, 3 cm from each side and 3.5 cm away from each other. Under each "X" mark label the dye which will be dropped on that "X". R is for red, B is for blue, G for green, Y for yellow, and UK for your unknown.

Preparation of the chromatographic developing chamber:

     Measure out 30 mL of solvent (a 0.1 % solution of sodium chloride in water) into a 600 mL beaker. Cover the beaker with a large watchglass to slow down the evaporation of the solvent.

Spotting the chromatography paper:

     Place one drop of each of the different colors of food dye in different depressions of your spot plate also include a place for your unknown. Use an open ended capillary tube (1 mm, O.D.) to practice applying small spots (about 3 to 5 mm) on a piece of paper towel. Use a different capillary tube for each different dye. When you are finished with the capillary tubes place them in the container, provided by the instructor, filled with water. These tubes can be washed and reused. When you have mastered the technique of spotting with a capillary tube, place a small spot of each dye on the appropriately labeled "X". Make sure the spots are applied exactly over the "X" mark for two reasons. First, if the spot is in the solvent this experiment will not work and secondly, for direct comparison you need to have all the spots start from the same reference point. Allow the spots to dry for 5 minutes.

The Experiment:

     Roll the paper into a cylinder and staple the sides without overlap. Place the lower staple above the baseline. Place the cylinder in the beaker with the solvent, make sure the spots are above the solvent line. Cover it with a watch glass to slow down the evaporation of the solvent. Leave the beaker undisturbed for about 20 to 30 minutes and allow the solvent to flow up the paper until it reaches the top line.

    At this point proceed to the next experiment but remember to keep an eye on the chromatogram.

After 30 minutes:

    When the solvent in the beaker reaches the 8.0 cm level, remove the paper from the beaker an allow it to dry on a paper towel or watch glass. When the paper is completely dry, remove the staples and outline the different colored spots lightly with a pencil. Fill out Table A on the report sheet then attach your chromatogram to the report form.

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Section 2: Scientific Method on Household Items

    In this section you will identify common household chemicals by their chemical properties then analyze a mixture of unknown composition. In general, a chemist will add a reagent (a known starting material) to a sample being tested and wait to see if a reaction occurs. A chemist will know a reaction has happened because some form of change will be observed (a positive result). Changes may include the formation of a gas, a color change, the formation of a solid, or the production of heat. If no change is observed, then a chemist may conclude the absence of a substance (a negative result). You will need to look for both positive and negative results in order to theorize what your unknown sample is.

In this experiment you will be using the following chemicals:

    Powders: Baking Soda Corn Starch Alka Seltzer Table Salt

    Liquid Reagents: White Vinegar Iodine Tincture Distilled Water

    A series of chemical tests will be performed that will help you discover how each of these powders react with each of the liquid reagents. It will be necessary for you to be very observant when you perform each of these tests. Make sure you record both positive results and negative results. Make note of occurrences such as the production of bubbles, a color change or no change at all. All observations you make are important. Your unknown sample is a mixture containing two of the above powders.

Collect the following equipment:

    A) Spot plate C) chemicals (powders & liquids)

    B) Disposable Pipets D) 3 small test tubes

PART A Observation and Identification of known samples

Acquire a spot plate and label in the same manner as the diagram below:

    ;White Vinegar

    ;Iodine Tincture