The Reaction Order of Blue Dye and Bleach

By. Chris Eisenhart, William Aldrich, and the One and only John Miller in your 8th period

Chemistry class. PROBLEM

Determine the order and rate of the reaction taking place when Blue No. 1 dye (food coloring) and sodium hypochlorite (NaOCl) are mixed together.

RESEARCH/BACKGROUND INFORMATION

The rate of reaction depends on the concentration of the reactants and can be expressed mathematically as the rate law: rate = k[reactant 1]m [reactant 2]n. In the equation, k is the rate constant and m and n are the individual reaction orders. The variables must be found by experimentation and cannot be found through stoichiometry. The rate constant is found by looking at the concentration of the substances per time. It is dependent on the reaction order.

Only the correct reaction order will give the correct rate constant. The overall reaction order is the sum of m and n. These variables can be zero, one, or two. In a zero-order reaction, the rate is independent of the concentration of reactant. A first-order reaction occurs when the rate is directly proportional to the concentration of the reactant. In a second-order reaction, the rate is the square of the concentration of the reactant. A graph of the concentration vs. time can be used to determine the order of a reaction with respect to a particular reactant. When looking at the concentration of one of the reactants, a zero-order reaction is [concentration] versus time, a first- order reaction is ln (the natural log) [concentration] versus time, and a second-order reaction is the reciprocal of a zero-order: 1/ [concentration] versus time. In our experiment, we are using

Blue No. 1 (blue food coloring) and sodium hypochlorite. To determine the concentration, we are using a colorimeter to find the absorption of light that the color in the solution has (the greater color concentration, the more light absorbed). The bleach will be in excess, so the concentration for it will remain constant. We will be looking at the blue dye. http://www.files.chem.vt.edu/RVGS/ACT/notes/rxn_order.html http://www.cartage.org.lb/en/themes/sciences/chemistry/miscellenous/helpfile/kinetics/rateorder. htm

Notes from lab packet

HYPOTHESIS

We believe the reaction will be dependent on only one substance, the blue dye, and will therefore be a first-order reaction.

MATERIALS

 Computer with USB port  PASPORT USB interface  PASPORT Colorimeter  DataStudio software  Vial of the dye FD&C Blue No. 1 (blue food coloring), 3 drops  Household bleach: sodium hypochlorite (NaOCl), 5.0 mL  Graduated cylinders (2), 10-mL  Beaker, 50-mL  Stirring rod  Water, distilled, 20.0 mL  Protective gear

PROCEDURES

1. Set up the computer along with the Colorimeter

2. Choose the correct DataStudio configuration file

3. Set up all equipment

4. QUICKLY pour the two solutions into a beaker and stir with the glass rod

5. Fill a cuvette with the mixed solutions and place cuvette into Colorimeter

6. Click “start” DataStudio

7. Observe remaining solution in beaker and record observations

8. After DataStudio is done recording, click “stop” 9. Find the best-fit line for each graph received to determine which order of reaction has

taken place

10. Save the DataStudio file and answer all questions on the Student Response Sheet

11. Clean up lab station DATA

ANALYSIS

In the lab in class today, my group combined a blue dye and bleach, so that we could determine the reaction rate and the reaction order. After placing the combination of liquids into the calorimeter, the calorimeter created three graphs: zero-order, first-order, and second order reaction graphs. Next, we had to Linear fit each graph, attempting to find the graph that fit the line best by evaluating the mean squared error. The graph that possessed the least mean squared error fits the graph best and is our answer for reaction order. Our group discovered that the zero- order reaction graph had the least mean squared error followed by the first-order and then the second-order reaction graphs. The first-order reaction and second-order reaction graphs had similar trends; both graphs followed the line almost identically until the end of the reaction. At the end of the reaction the first and second- order graphs veered abruptly away from the line causing the mean squared error to be greater. Our group ran the experiment smoothly; however, we believe that we could have ran the test quicker and received different results for our reaction order.

CONCLUSION

Today, our group learned that the reaction order of this experiment was one because it had the least mean source error. This means that the rate is independent of the concentration of the reactants, which makes our group hypothesis correct. In the prediction, we predicted that the reaction order would be zero, and would thus have no effect on the reactants. Our group believes we had no source of error. Nonetheless, we could have moved faster and got different results that would have changed our answers, and given us different mean source errors. Ultimately, we could have received a totally different answer based on the speed in completing the experiment. BIBLOGRAPHY

Sibert, Gwen. “Reaction Order.” www.files.chem.vt.edu. Nd. Roanoke Governor’s Valley School.

N.pag. Web. 12 January 2011.

“Rate Constants and Order of Reaction.” www.cartage.org. Nd. Learn. Chem. Vt.Edu. N.pag.

Web. 12 January 2011.

I’ve got the Chemistry Blues