Chem IA: Redo Experiment?

[ABKor752]

Hello all! So, I have a slight issue with my Chemistry IA. My topic is on the enthalpy change of solutions of instant heating and cooling packs. The research question is "How do 5.000 grams of different chloride salts (magnesium, calcium, strontium, iron (III), zinc) affect the total enthalpy change of solution of an instant heating or cooling pack when dissolved in 50.0 mL of water?" Basically, that is the complicated way of saying that I dissolved salts in water and tracked the temperature of the solution over time.

I completed my experiment and wrote a good chunk of my IA before first year of IB ended. The issue, however, is that my experiment went... wrong, in different ways. First, comparing my data with accepted values, I had like a 65% error in my data, making it really difficult to come to an accurate conclusion on. Furthermore, my supplies were slightly faulty as the temperature sensor shut off randomly during one trial and the automatic stirrer I was using "malfunctioned" in the middle of two trials. Additionally, I am pretty sure that I used sodium chloride instead of magnesium chloride for my experiment, because my measured value ended up being +3.5 kJ/mol when the accpeted value was -155 kJ/mol. Clearly, then, I cannot come up with a basic conclusion on faulty data like this. And given that a lot of my data is already inaccurate (with the 65% error mentioned earlier), I realized that I should change my material settings to help track more heat while the trials are running. And finally, and probably the most important issue, any conclusion that I make out of this will be very difficult. My goal is to see any trends in enthalpy change of solution when going down the periodic table (magnesium, calcium, strontium) and going across (calcium, iron (III), zinc). I have not been able to find much research on this, so it seems like any conclusion I come up with will be theoretical (i.e. the data may have resulted because of this one factor, but I'm not sure).

Anyway, that is a lot of information. The final draft is not due at our school until November, so I am not stressing out about it too much. I just want to make sure I know what to do, and ultimately whether I should redo any part or all of my experiment.

 

Thanks for your help!

 

 

[kw0573]

If the salt is outside of the cold/heat pack, I am unaware of how it contributes to enthalpy change much different from pure water. You should double check your sources. The only changes salt in a solution that I know of is that it lowers the melting point and increases the boiling point. The enthalpy should not change because enthalpy is dependent upon the reaction and the salt solution is not part of the reaction. The temperature may change, but temperature is different from enthalpy. 

If I am mistaken, then you should rerun all experiment, being more prudent this time. If I am correct in saying you are not doing much chemistry in this experiment, you should revise your topic and do experiment for the new topic.