Experiment 1

Analysis of the Color of Water Soluble Inks

Purpose, Conclusions and Extensions

Purpose

Recall, if an ink separates into several dyes of different colors, then those individual dyes must have been responsible for the color of the ink. Using this and the nature of the different subtractive primary colors, it is possible to identify the origin of the color of an ink.
Using the colors of the dyes and the value of the R_f for a dye, it is possible to determine if two inks use a common dye. In these experiments the individual inks from the different pens are the independent variables and the colors of the spots and R_f's are the dependent variables.
Finally, different solvents can change the effectiveness of a separation by changing the values of the R_f's. This can be investigated by chromatographing the inks several times with different solvents. In this experiment the composition of the solvent is the independent variable and the values of the R_f's are the dependent variables.
There are three parts to the purpose of this experiment. In general, they are to determine:

• the origin of the color of inks in various pens by separating the dyes contained in the inks using paper chromatography.
• if the dyes used are common to several inks by comparison of chromatograms and R_f's.
• the effect of solvent composition on retention of dyes by varying the solvent used for the separation.

At the beginning of your report in your notebook, you must write the purpose of your experiment. You can follow the format from above, but be specific. For example, which inks are you studying? Which solvents are you using? Use the purpose section to ask the specific questions that you are trying to answer with your experiment.

Conclusion

The conclusion section which you include at the end of your report in your notebook is very closely related to the Purpose section. In the Conclusion section, answer each of the questions you wrote in your Purpose. Base your answer on the data you reported in the Results section.
For example,

• Give a specific explanation of the origin of the colors observed for each ink. In your explanation refer to the subtractive primary colors which are used in the inks. How do these primary colors result in the color of the inks?
• Are there any dyes which are used in more than one ink? How do you know this? Use the colors and R_f's as evidence to convince the reader that your conclusion is supported by evidence..
• How does the change in solvent affect the separation? Refer to the specific values of the R_f's to illustrate your conclusion. Does this tell us anything about how the dye prefers the paper or the moving solvent?

Extensions

Can you suggest any extensions to this experiment? Think about changing the independent variables and the dependent variables that you could measure or observe. This may suggest new experiments that you could propose for your project or try later for your classroom.