Can I change two variables at a time?

[faeriedust5]

My project is on the Effect of Particle Size and Temperature on the Rate of Chemical Reaction. I'm using Alka-seltzers to test my experiment. Basically, I'm trying to find out which size particles (size of the alka-seltzer tablets such as whole tablets, broken tablets, and powdered tablets) and which temperature (hot, warm, or cold) will make the alka-seltzer dissolve faster. One of my friends said I'm testing two variables at a time so it wont be accurate. I already finish the experiment and everything turned out perfectly fine. First I tested the whole tablets with 3 different temperatures, then broken tablets with 3 different temperatures, and lastly powdered tablets with 3 different temperatures. Am I changing two independent variables at the same time? Am I allowed to? Please reply ASAP

[faeriedust5]

My project is on the Effect of Particle Size and Temperature on the Rate of Chemical Reaction. I'm using Alka-seltzers to test my experiment. Basically, I'm trying to find out which size particles (size of the alka-seltzer tablets such as whole tablets, broken tablets, and powdered tablets) and which temperature (hot, warm, or cold) will make the alka-seltzer dissolve faster. One of my friends said I'm testing two variables at a time so it wont be accurate. I already finish the experiment and everything turned out perfectly fine. First I tested the whole tablets with 3 different temperatures, then broken tablets with 3 different temperatures, and lastly powdered tablets with 3 different temperatures. Am I changing two independent variables at the same time? Am I allowed to? Please reply ASAP

[donnahardy2]

Hi,

You did 3 different controlled experiments, so your results are valid. In each experiment, you had only one parameter that changed (temperature), and all other conditions were controlled. The independent variable was temperature, and the dependent variable was time. If you had tested whole tablets, pieces, and powder, all at different temperatures in the same experiment, then that would have been an uncontrolled experiment. For a science fair project, it would be slightly better to do one experiment twice and try to duplicate your results, rather than to do 2 or 3 experiments just one time. So, if you have time, and you did each experiment just one time, do repeat your experiments and include all the results on your project board.

Donna Hardy

[kgudger]

Hello and welcome to the forums!

Yes, you're testing 2 variables, but that should be OK. As long as you controlled all variables except 1 in each experiment, you're OK. It sounds like your experimental design was a good one.

My only suggestion would be on repeatability - did you repeat your experiments more than once at each point? It's always a good idea.

Keith

[faeriedust5]

Ohhh I see. Yes I've tested my experiment at least 3 times Thank you for your help!

[faeriedust5]

Thanks for replying! Uhm I see what's going on. As long as my results are valid I think I'm fine. Next time I should just do one independent variable. And yes I've tested my experiment at least 3 times to make sure my results are accurate. Thank you very much!

[donnahardy2]

Hi,

Results in triplicate with 3 separate experiments. That is excellent! The science fair judges will be impressed with your thoroughness. And yes, next time you only need to do one experiment to meet the minimum requirements of a science fair experiment. It's definitely OK to do more, however.

Donna Hardy

[Craig_Bridge]

Just to be clear, 3 table sizes x 3 temperatures x 3 trials = 27 experiments. If you didn't do 27 experiments, then you probably didn't do 3 trials of each combination.

[ChrisG]

Hi, I have merged your two topics into one. Please keep all posts related to your project in this topic so that experts can keep track of your progress and the replies that you have already received.
Thanks.
Chris

[sciencebuddy]

I don't think you are necessarily changing two variables at the same time, but your methodology appears to cover all your tracks.

It is VERY important that you make sure the particle size of each type remains consistent however.

Also, do 3 trials for each of the 9 experiments you are running

Good luck!
-Dan