Fillable pdf

Mixtures are defined as materials which contain at least two pure substances, which can be separated by physical means. Pure substances, elements and compounds, CANNOT be separated using physical means (i.e., using a method which does not break any chemical bonds). In this virtual lab, you will use a physical separation method (paper chromatography) to compare different kinds of known inks (which are mixtures) with an ink sample from an unknown source. Through the comparison of your data, you should be able to identify the source of your unknown ink.

Ink is typically a mixture of some sort of solvent and one or more colorant materials. The solvent is commonly either water or some sort of oil (e.g., soybean oil), and is used to dissolve the other ink components in the ink mixture. The colorant is the substance used to give color to the ink and can be either a dye (small molecules which can be dissolved) or a pigment (much larger molecules which cannot be dissolved). Finally, many inks contain special additives to improve the properties of the ink (e.g., fungicides, biocides, resins for resilience, buffers to control the pH, and humectants to reduce evaporation of the solvent). When you write with an ink pen, the ink’s solvent evaporates and leaves behind the non-volatile residue. (Source: www.misterinkjet.com)

In order to analyze a mixture such as ink, we need to employ a means of physical separation. One method of physical separation which is ideally suited for analyzing ink is called paper chromatography. A small amount of the mixture of interest is placed as a dot at the bottom of a strip of special “chromatography” paper. Some type of solvent (which may be a either a single pure substance or a mixture) is then allowed to wick up through the paper and carry along the components of the mixture as it travels upwards. The different chemical components of the mixture travel at different rates, which results in a separation along the height of the paper. This process of allowing the solvent to travel through the paper is referred to as “ developing” the chromatogram. If the chemical substances happen to be colored species, then they can be easily seen as different colored spots or streaks along the paper.

The physical property which results in the separation during any chromatography experiment is the preference for a substance within the mixture to stay in one phase more than in the other phase. In the specific case of paper chromatography, the two phases are the paper phase (i.e., when the substance is adsorbed onto the paper) and the solvent phase (i.e., when the substance is dissolved in the solvent). The reason why a substance would prefer one phase or the other lies in its chemical structure and corresponding physical properties. For example, chemicals which are hydrophilic (polar substances which are attracted to water or “water-loving”) would behave differently from chemicals which are hydrophobic (nonpolar substances which avoid water or “water-fearing”). The hydrophilic chemicals would be expected to move up the paper much more rapidly than hydrophobic chemicals if water was used as the developing solvent.

Who Kidnapped Fluffy?!!

Scenario: You are a Chemical Analyst assigned the task of identifying ink from a ransom note left at the scene of the kidnapping. Fluffy, a valuable pet Persian kitty has been swiped, and the thieves left a hand-written note using some sort of black ink pen. In the room where the note was left, several different black ink pens were also found. The detectives have obtained unique fingerprints from each of these pens. They are hoping that, if the correct pen can be identified, then the corresponding fingerprints can be used to identify the thief. Your mission is to determine which ink pen was used!

The Procedure used to develop the chromatograms was:

1. 4 strips of chromatography paper were dotted with ink in the bottom center of each paper. The central dot corresponds to the ink used in the ransom note.

2. A ruler and a pencil were used to draw a line through the unknown ink dot on 4 strips of chromatography paper. Near the very top of the opposite end of the paper, “Acetone” was written on two of the strips and “Alcohol” was written on the other two strips. The strips were also dotted using the pens found at the abduction site. Those pens were labeled “1,” “2,” “3,” and “4.” The numbers corresponding to the pens found at the crime scene were marked on the chromatography paper using a pencil.

3. Two different solvent systems (acetone/water and isopropyl alcohol/water) were prepared.

4. Two chromatography papers, labeled “Acetone,” were placed in the beakers containing the acetone/water solvent mixture with the ink dot edge at the bottom. The other two chromatography papers, labeled “Alcohol,” were placed in the beakers containing the isopropyl alcohol/water solvent mixture with the ink dot edge at the bottom.

5. The chromatograms were developed. Watch the video linked in Falcon Online Content to see the procedure AND the data!