Question about control in my chemistry experiment

[lena96]

Hi, my name is Lena and I have a question that regards to controls. My experiment: Does the citrus level in organic fruit differ in non organic fruit. I will be testing different citrus fruits: orange, lime, lemon, and grapefruit. I will be taking 3-5 samples from each. 3-5 organic from orange and 3-5 non organic from orange. It is the same for the rest. My question is, what can be the control of this experiment? Thank You!!

[deleted-71934]

Hi Lena, there are many different factors in your experiment which you could keep constant through-out your series of experiments. For example, you could try to use the relatively same size of the fruit from the organic and non-organic sources, or , for a more global constant, do the tests all at the same air temperature.

Here is the link to the science fair variables guide: http://www.sciencebuddies.com/science-f ... bles.shtml
Hope this helps, and good luck with your experiment!

[deleted-71588]

I'm not sure what you mean by "control"? In any compare and contrast experiment like comparing brands of paper towels, you arbitrarily pick one "brand" as the "control group" and compare and contrast the other "brands" to the control group.

In your proposed experiments, each type of citrus fruit (oranges, lemons, grapefruit) would have to be run independent of the other fruit types.

If you are trying to determine differences based on "organically grown" vs "use of non-organic fertilizers and pesticides in the orchard", you have a significant variatals issue. The genetic variatals of oranges (Bahianinha, Berna, Blonde, Maltese, Cara Cara, Dream Navel, Hamlin, Jaffa, Jincheng, Kona, Late Navel, Moro, Moro Tarocco, Navelina, Parson Brown, Pera, Rhode Red, Roble, Salustiana, Sanguinelli, Shamouti Jaffa, Valencia, Washington Navel, California Navel, African, Argentine, Bergamot, Bigaradier Apeupu, Daidai, Chinotto, Gou Tou, Seville, Tunis) could easily produce different results. Some variatals are more pest resistant so organic farmers will tend to use them. Other variatals produce more/better fruit with with specific non-organic growing conditions and will be preferred by traditional orchards.

Unless your organically grown produce is the same variatal as the non-organically grown ones, you have an uncontrolled difference which could easily be responsible for some or all of any difference you detect.

Given all the complexities of coming up with an experiment that attempts to control all differences other than one independent variable (organic vs non-organic), I recommend experimenting with only one fruit type. Pick the type of fruit where you can get organic and non-organically grown fruit of the same variatal.