Science Buddies: "Ask an Expert"

I'm planning on doing the Presto from black to clear photochemistry project for my science fair with different coloured lights. But I'm just wondering if anybody could tell me the controlled, dependent and independent variables for this project. I have some sort of idea but am if-y about this.
I need an answer ASAP.

Hi,

I read the procedure for the photochemistry project and as far as I can tell the independent variables are the light sources you used and the length of time that you exposed the iodine solution to the light. Independent variables are the things you do in an experiment. The dependent variable is what you measure, in this case the color of the solution at various times by comparing it to the standards. The controlled variables are the concentration of the ammonium oxalate and iodine.

I hope this answers your questions. If you still need help let us know.

Sybee

Hello I was wondering if the oxalic acid had to be lab grade

Hi Brandon,

The oxalic acid can be commercial grade from a home store. It doesn't have to be reagent grade. I used to buy oxalic acid from the drugstore but i don't know if it is still sold that way.

Let us know how your experiment turns out.

Sybee

I did this project. In the beginning its says to label 6 tubes, 100%,50%,12.5%,etc. then later on it says label 5 new tubes 1-5, these are the tubes it says to put in light. So my question is what are the 6 tubes for?(the 100%,50%,etc)

The project your are doing is "Presto! From black to clear." https://www.sciencebuddies.org/science- ... #procedure

In the Procedure Section it says:

First you will make a set of standards by which to compare the color changes that occur in the test samples. Put on your safety goggles and a pair of disposable gloves. You should also wear clothing that you do not mind getting stained.
Use masking tape and the permanent marker to label six centrifuge test tubes, as follows:

100%
50%
25%
12.5%
6%
0%

The next set of five tubes that you set up are for the actual experiment:

Observing the Tubes

Record the change in color of each tube at varying times, such as 15 minutes, 30 minutes, 1 hour, and 4 hours.
Compare the color of each tube to the standards to estimate how much of the color has been lost due to light exposure.
Record your results in your lab notebook.
Make a numerical scale from 1 to 6 for the color of the standard solutions. Use this scale to graph your results. Graph time on the x-axis and color on the y-axis.

That's why you have to have two sets of tubes--so you can compare the color to what you get from a known concentration.

Sybee