Water Electrolysis

In chemistry today, we used a battery, a cup with conductive tacks punched into it, two small test tubes, pH indicator, and deionized water to identify the production of hydrogen and oxygen gases. The balanced equation for the reaction was 2H20–> 2H2+ O2, and there was qualitative data that supported this chemical reaction. Visually, there was a difference in amount of gas produced. Twice as much hydrogen was produced in comparison to oxygen. To ensure this observation, we used a pH indicator in the test tubes to differentiate the gases. The oxygen turned blue, while the hydrogen turned red.

Without pH indicator.

With pH indicator.









Quantitative data could also ‘prove’ the balanced reaction, by way of measuring the amounts of hydrogen and oxygen produced. This could be done by measuring the mass of the solution prior to the reaction, and comparing it to the mass after the gas production. If measurements were taken, the masses should have a two mole: one mole ratio. Particle diagrams such as the one below can also model what occurs in this reaction.

Three Questions 8/14/14

1. What tasks have you completed recently? 

Recently, I have completed all of the tasks necessary for “back to school”, including supply shopping, schedule rearranging, and laptop shopping. Regarding school assignments, I have completed a chromatography lab and numerous calculus assignments.

2. What have you learned recently?

Recently, I have learned that time management is an essential this year. With six AP classes and multiple club offices, it is going to be a very busy year, and I need to rise to the occasion. In terms of classes, I have reviewed chemistry and pre-calculus concepts, learned about emotional appeals, and discussed the basic concepts of psychology. In chemistry, I learned that the process of chromatography is used to physically separate dyes through a lab experiment.

3. What are you planning on doing next?

Next, I am planning on scheduling out my month in order to stay organized and on the ball with my classes and extra curricular activities. Also, I plan to join cross country and begin guitar lessons.

Chromatography Lab

In chemistry, chromatography is used as a physical separation technique for mixtures. Our most recent experiment utilized this technique for dye separation. Dyes are put together physically, not chemically, so they can separate using this method.

In the experiment, we followed the scientific method in multiple ways. To begin with, FD&C dyes were used as a control; in addition, different solvents were used. This meant that the experiment followed the scientific method strictly.

Finished products!

Finished products!

For the experiment, nine sheets of rolled paper, each with a set of dye dots, were dipped in three different mobile solvents. There were three different types of dye: FDC, Cra-Z-Art, and Vis-a-Vis. The three solvents were chromatography solvent, alcohol, and sodium chloride. The papers used were also a solvent, but they were stationary solvents, not mobile. The dots of dye on the paper landed just above the mobile solvent line, never touching the liquid. When the papers sat in the solvents for extended periods of time, the dye began to migrate up the paper along with the solvent. The rate at which the dye moved was dependent on the level of attraction between the dye and the paper. The more attracted the dye was to the paper, the less vertical movement occurred. From our experiment, we deduced that the nature of solvents and dyes follows a “like dissolves like” pattern because of shared chemical structure. Similarly, the different attraction levels observed throughout the experiment were determined to be the result of different chemical composition, or molecular structure.

Our conclusions can be supported by both qualitative and quantitative data. In terms of quantitative data, the proof is simply in the papers themselves. It is apparent that the color of the dyes changed as a result of the experiment. Regarding quantitative data, it is possible to calculate the extent of dye movement in relation to the mobile solvent by using a retardation factor formula. A retardation factor formula is the distance from the pencil line on the bottom of the paper to the dot, divided by the distance from the pencil line to the solvent front near the top of the paper.

\ R_f = \frac{\mbox{migration distance of substance}}{\mbox{migration distance of solvent front}}

Retardation Factor Formula

I calculated the Rf factor for the FDC dye and alcohol solution, and the Cra-Z-Art dye and NaCl solution.For the FDC, I measured 4 centimeters for the migration distance of substance, and five centimeters for the migration distance of solvent front, resulting in a retardation factor of .8. The Cra-Z-Art dye migration distance of substance measured 2.33 centimeters, and the migration distance of solvent front measured 3.5 centimeters, resulting in a Rf of .66571.

Thin Layer and Column Chromatography

Chromatography Dye Movement Diagram


Another way to explain why some dyes travel further is particle diagrams. The more attracted the dye is to the paper, the less vertical movement. The image above exhibits the vertical movement of dye along with solvent and the level of dye separation, while the image below shows how our dye movement appeared on one of our papers.

Badly Drawn Particle Diagram.

This lab was quite useful for the reason that it reinforced my previous understanding about chemical/physical properties and changes. It reminded me that solubility is always a physical change, because bonds are not broken, only dissolving occurs during the process. Similarly, it reinforced my knowledge that while color change is an indicator of a chemical change, occasionally this is inaccurate and the change is only physical. My previous understanding about matter classification and separation techniques was also reinforced, because I was reminded that matter is classified by atoms, diatomic atoms, compounds, and mixtures. In this lab, we were working specifically with homogenous mixtures. In terms of separation, it reminded me that separation techniques have to match the type of mixture trying to be separated.