Samantha D.

asked • 02/03/21

What materials do I need to complete a 2 x 30 experiment comparing vitamin c concentrations in an orange compared to store-bought orange juice?

-Need measurements for materials

-2 x 30 meaning testing 2 variables and gathering 30 samples of each

Shelli D.

Hey, Samantha. Honestly, you're going to need quite a few things. I did this experiment with my students a while back and so I'll share the list of materials I used. Good Luck on your Biology journey! To compare the vitamin C concentrations in an orange and a store-bought orange juice, you will need the following materials: • A fresh orange and a store-bought orange juice of your choice. Make sure the juice contains vitamin C and check the label for the amount per serving. • A blender or a juicer to extract the juice from the orange. • A scale to weigh the orange and the juice. • A mortar and pestle to crush a vitamin C tablet containing a known amount of vitamin C. This will serve as your internal control standard. • A 0.005 M potassium iodate (KIO3) solution as your primary standard. You can prepare this by dissolving 0.356 g of KIO3 in 1 L of distilled water1. • A sodium thiosulfate (Na2S2O3) solution as your titrant. You can prepare this by dissolving 12.5 g of Na2S2O3 in 1 L of distilled water2. • A starch indicator solution to detect the endpoint of the titration. You can prepare this by dissolving 0.25 g of soluble starch in 50 mL of near boiling water2. • A 1% potassium iodide (KI) solution to generate iodine from KIO3. You can prepare this by dissolving 10 g of KI in 1 L of distilled water2. • A 6 M hydrochloric acid (HCl) solution to provide acidic conditions for the reactions. You can prepare this by diluting 50 mL of concentrated HCl (12 M) to 100 mL with distilled water2. • A 20 mL pipette and a pipette filler to transfer the sample solutions. • A burette and a stand to deliver the Na2S2O3 solution. • A 250 mL conical flask to perform the titration. • A white tile to place under the flask to observe the color change. I know it's a lot, but if you're able to get a hold of everything, it's a pretty cool experiment. Let me know if you need any more help with this one!
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01/22/24

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Stanton D. answered • 03/04/24

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Some additional comments to Shelli D.'s excellent comment! This is supposed to be a "2 x 30" design -- but, it's not exactly clear what this refers to, since if you consider the packaged juice vs. freshly-squeezed juice as one variable, why you need 30 samples of the latter (30 different brands of packaged juice? Really? And how would that relate to 30 different oranges, either from the same store or from 30 various stores? Are you really wanting to test different varieties of oranges, or is your working hypothesis that some stores' oranges will be different than others'? As a test of shelf life of Vit. C in fresh oranges? Should this be compared with the packaged juices from the matching stores? Or maybe the intent is to test 30 replicates from just one bottle of juice, as the juice is expensive; 30 oranges is OK but bear in mind that handling of the samples is critical, the Vitamin C will be degrading continuously after they are squeezed, and so on. In other words, don't squeeze your 30 samples first, then test them subsequently.

So go for it, but plan to spend some time getting your technique and equipment worked out, testing reproducibility with replicates, etc. before you start gathering formal data.

-- Cheers, --Mr. d.

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