[mkurek]

Hi so I'm on a team at school that builds a car for this competition, and we use an iodine clock that is rigged up to a light sensor for timing purposes. We've been having problems with our data being very inconsistent. We'll use the exact same volumes/concentrations of reactants (all from stock bottles that are shaken), yet the times vary up to 25 seconds. Any thoughts on why this might happen?

And along the same lines, does anyone know of any good clock reactions with distinct physical changes that accompany them?

[billnotgatez]

Do you have charts for factors other than concentration that may effect rate of reaction.

[mkurek]

The testing is done in a unit ops lab that is maintained at 25 C. Not sure what other factors might effect the rate.

We use starch as our catalyst.

[billnotgatez]

According to WIKI there are several ways to make a Iodine clock.
http://en.wikipedia.org/wiki/Iodine_clock_reaction
Could you list all the chemicals and concentrations and volumes.
I may not have an answer but someone else may after seeing what you are doing.
I was asking for charts to see if slight changes in a variable would cause a large change in reaction rate.   I have never played with a Iodine clock, so I was hoping for some documentation or someone else insight.
I will put Iodine clock on my to do list.

By the way WIKI also has some other chemical clocks listed
http://en.wikipedia.org/wiki/Clock_reaction
I did not look at them closely to know if they would be of help.
I wonder if you GOOGLE chemical clocks what would be the result.

[mkurek]

Well we actually do have some graphs made up from last year's competition that we used to calculate the rate constant and what not but there's really not any detailed data logs I can easily provide you with. I was just wondering if anyone might have an idea of what could effect it so much.

One thing we did notice was that freshly made solutions performed differently than our stock solutions. <- I feel like this is the biggest indicator of our problem.

And we use potassium iodate and sodium bisulfate, pretty sure there that's the most standard way of doing it. Now the chemical clocks thing we have looked into, but we use a light sensor rigged up to the iodine clock to cut the power to the engine on our car. So a lot of the chemical clocks out there that just change to different colors would be a lot more difficult to use.

[billnotgatez]

@mkurek

we use potassium iodate and sodium bisulfate

Do you mean potassium iodate solution added to sodium bisulfite solution?
http://en.wikipedia.org/wiki/Iodine_clock_reaction#Iodate_variation

If I understand you correctly, you get more consistent results
if you make a fresh solutions of potassium iodate and sodium bisulfite using precise measurements and pure clean dry solids with a consistent water source.
And you are getting inconsistent results using stock solutions off the shelf that may have been sitting for a while.

If you use GOOGLE

sodium potassium iodate shelf life
sodium bisulfite solution shelf life

I think you will find your answer.

It would be nice if you post your findings here.

[mkurek]

Yes I meant to write bisulfite and I'll be sure to post our findings. I think what we're going to try is actually weighing out super tiny amounts of each reactant every time and seeing if we get more consistent results.

And yeah I never even thought of googling shelf life. I guess I kind of figured since it's not exactly a food item it isn't perishable, but clearly that train of thought was wrong.

If you're interested in knowing what this is for, check out this link: http://www.aiche.org/community/students/chem-e-car

[billnotgatez]

I wanted to see what results you got from the shelf life information

I will give you another hint
sodium bisulfite solution shelf life
although you may not find it directly you will see what related compound are like

nice site