Iodine Clock Lab

[IOwnAndPwnU]

Hi everyone,

I'm doing a lab on determining the rate expression for the iodine clock reaction (i.e. mix potassium iodate with varied concentrations with starch), along with the rate of reactions for each level of concentration. I'm wondering what type of stuff should I mention in the conclusion.

For the scientific explanation, I was thinking about writing about the collision theory and rate expressions. Am I missing anything?

For the error analysis/improvements, I was going to write about the consistency in mixing the two solutions together, cleanliness of test tubes, and explaining the large error bars (for my data specifically). Are there any other suggestions/improvements/sources of error I can add to my lab?

Thank you!

[Drake Glau]

Sounds good to me. Your IV is the concentration and if you tie collision theory with that real well it would greatly help your conclusion (assuming your data backs it of course)

[Keel]

Your conclusion should describe the 'science behind the experiment' i.e. how the experiment works in terms of chemistry. You should also describe how you were able to reach your final answer i.e. how you interpreted the data and processed it (the total error in the answer should be included). As for the evaluative process, hopefully this will help:

What you should be provided with is a literature value for the experiment you have done. This is important because it is an indication of how accurate your experiment was. So the first step is to find out how 'off' your obtained value (the answer reached in your DCP) in comparison with the literature value. This can be done by calculating the % difference:

[(obtained value - lit. value) / (lit. value)] x 100% = % difference in answers

This % now gives an indication of how inaccurate your experiment was. There are now two types of errors or areas of improvement you should consider. The first is improving the equipment that you used in your experiment, thus reducing the effect of random uncertainties; and the second is improving the way the experiment was conducted, or fixing the systematic errors.

You should now comment on which type of error contributed most to this inaccuracy. In your DCP, you should have calculated the total % error due to random uncertainties (ie the +/- ...% at the end of your answer). You can use this to find out what % was caused by systematic errors.

(% diff in answers)% - (total error caused by random uncertainties)% = (total error caused by systematic errors)%

You now have an indication of which error is more responsible for your inaccuracy. It is usually the systematic error. You then state which error is more responsible. You should then proceed to state improvements for both types.

For the first type, random uncertainties, go through all the equipment you've used in the experiment, state the % error they caused and propose an improvement. e.g. 50 cm3 measuring cylinder; +/- 0.5 cm3 caused a 10% error; propose to use a 50 cm3 pipette.

The second type usually requires some imagination and a general understanding of the limitations to the experiment. What systematic errors could have caused inaccuracy? State this systematic error, state which direction it moved your result, state whether it's a minor or major error, and state an improvement. e.g. Heat Loss; Caused obtained value to be higher than actual value; Major error; Use insulative container.

I hope this helps, remember this all comes from a chemist and you should adapt it for your purposes.

P.S. The chemistry forum has some good IA help resources if you need further help:

Also you should check the mark scheme: http://ibchem.com/IB/ibe/IA-2009.htm

More information regarding the IA, including the mark scheme, can be found here: