Science Buddies: "Ask an Expert"

Hi,
I am working on the experiment on your website "Which Orange Juice Has the Most Vitamin C? I am now on under the experimental procedure I am currently working on number 10 letter c. I am trying to figure out how to calculate the sample equation x/6.8 ml = 20 mg/8.5 ml = 16.0 mg so that when I start this experiment I can calculate vitamin c using my data. Please Help! (Please see) https://www.sciencebuddies.org/science- ... p044.shtml (FULL EXPERIMENT ATTACHED)

Hi,
Euation 10.c in the writeup is incorrect, as you politely point out. It should be

X = (6.8 mg/ml)*(20 mg)/(8.5ml) = 16.0 mg

I will ask the Science Buddies staff to correct this goof. Thank you for pointing it out.

Best Regards,

Barrett L. Tomlinson

Now I get it! Thank you so much for your prompt response!

Ivt - I'm sorry you ran into trouble with the faulty equation in the project idea on the Science Buddies site, but I'm glad Barrett was able to help out with the correct equation!

We've updated the project idea.

Good luck with the project!

Amy
Science Buddies

Hi. I am also planning to do the experiment "Measuring Vitamin C," but instead of Orange Juice I am going to use Lemonade. Although I have already begun my research and read everything posted here in Science Buddies, I still have a few questions. These are:

1.) I would like to make fresh squeezed lemonade but lemonade is lemon and sugar unlike the fresh squeezed orange juice which is just oranges. If I make a recipe and include my ingredients and measurements in the materials section, would that be okay?

2.) Are there any special requirements for the Vitamin C tablets? I noticed in the store there were different sizes. I was thinking the larger, the better but am not sure.

3.) Can you confirm that I can use Corn Starch as my soluble starch? Last year, my mom helped my sister with an experiement -- measuring the amount of iodide in salt -- and they ended up using laundry starch. My mom is helping me with this project and we both noticed in one of the e-mail threads that Corn Starch was suggested so then we looked up what Soluble Starches were and it looks like corn starch is one of them.

4.) Can I just use regular iodine that you buy in the pharmacy or do I have to order or look for one of the iodine solutions mentioned in the project.

Thank you!

Sincerely,

Sophie Schifter
6th Grader

4.) Can I just use regular iodine that you buy in the pharmacy or do I have to order or look for one of the iodine solutions mentioned in the project.

The iodine solutions used in titration experiments are different from the solutions usually used for antiseptic purposes. Tinctures sold for antiseptic purposes are usually water+ethanol+iodine, and iodine solutions for titration are water+iodine+potassium iodide, no ethanol. You can try reading the ingredients of iodine solutions available at the pharmacy, but unless you find one called "Lugol's iodine" the experiment really might not work properly.

http://en.wikipedia.org/wiki/Iodine#Dis ... _treatment

2.) Are there any special requirements for the Vitamin C tablets? I noticed in the store there were different sizes. I was thinking the larger, the better but am not sure.

It probably doesn't matter much. Things will likely be easier for you if you (1) pick something that dissolves quickly rather than a lozenge that's designed to dissolve slowly and (2) avoid anything with a gel or capsule-like coating that would be difficult to work with -- although if you can split the capsule open and dump all the powder out instantly, that could work very well.

1.) I would like to make fresh squeezed lemonade but lemonade is lemon and sugar unlike the fresh squeezed orange juice which is just oranges. If I make a recipe and include my ingredients and measurements in the materials section, would that be okay?

Orange juice contains plenty of naturally occurring sugars, so if the chemistry works with orange juice I would expect it to also work with added sugar in lemonade. What you want to keep in mind is the idea of concentration and dilution. For example, if your lemonade solution is 1 part lemon juice to 4 parts water, 1 cup of lemonade will have 20% as much vitamin C as 1 cup lemon juice. If your objective is to find out whether drinking the same volume of lemonade or OJ provides more vitamin C, it makes sense to compare OJ to lemon juice diluted and mixed with sugar in a drinkable recipe.

If you are concerned about the specific requirements and grading of your project, you should talk to your teacher. However, for scientific accuracy you should explain everything you did, including the lemonade recipe. The example I gave above could be described as "a 20% solution of lemon juice in water with X g/ml sucrose" (depending on how much sugar was added) -- more info about calculating concentrations here: http://en.wikipedia.org/wiki/Concentration

One thing to keep is mind is that there will be variation (in acidity, sweetness, vitamin C concentration, etc) among species of lemons and locations in which they were grown, seasonally, and even between two lemons that are sitting next to each other on the grocery-store shelf. You could repeat the experiment on the juice of several different lemons separately to get an idea of the variability. (Orange juice and anything manufactured on a large scale will have mixed together the juice of hundreds or thousands of oranges together at once, eliminating a lot of the variation.)

3.) Can you confirm that I can use Corn Starch as my soluble starch? Last year, my mom helped my sister with an experiement -- measuring the amount of iodide in salt -- and they ended up using laundry starch. My mom is helping me with this project and we both noticed in one of the e-mail threads that Corn Starch was suggested so then we looked up what Soluble Starches were and it looks like corn starch is one of them.

I'm not completely sure about this, but it's probably less risky than using the wrong iodine solution. There is soluble starch, pure amylodextrin, available from one of the suppliers recommended. My guess is that corn starch is a mixture of many different related compounds, some of which react with iodine and some of which may not. Since the exact concentration of soluble starch is not critical, I would expect corn starch to work, although it might contain additional ingredients that could make the solution more cloudy.

http://www.hometrainingtools.com/starch ... CH-STARCH/
http://en.wikipedia.org/wiki/Dextrin

Amanda

I think I ran into a big problem in my experiment unless I am reading the results wrong. I tested the Vitamin C for 4 different types of lemonade: fresh squeezed, refrigerated, frozen and a juice box. The juice box took the longest time to neutralize, by far, then the frozen, then the refrigerated, then the fresh. Doesn't that mean that the juice box had the most Vitamin C to start? I hypothesized that it would be the exact opposite. Do you think I did something wrong? I was very careful with my measurements counting both drops (which varied) and the amounts of beginning and ending liquids.

If you ran the test multiple times (need at least three attempts with each product) and got consistent results, then you were sucessful, you disproved your hypotesis.
If you only ran the test once per product, you can't be sure that your test is repeatable, so you aren't done testing so you can't draw any conclusions yet.

Using the sceintific method to prove or disprove a hypothesis can only provide new information if you can't be certain about what the outcome will be. Disproving something you thought was valid is often the way that scientists make great strides in understanding.

Vitamin C, ascorbic acid is often used as a preservative in processed foods and is often added. I'm personally not surprised that the juice box showed up with the largest concentration. There are both preservative and marketing reasons why a producer would want their nutritional labeling to show high vitamin contents, the "See, our product isn't just empty calories, it has significant vitamin content".

-Craig

I ran the experiment 3 times and my results were similar for each run through. I also noticed that the juice box said on it, 100% Vitamin C so I also figured that they added in the Vitamin C. Thanks as always Science Buddies!!!

CodyS wrote:I also noticed that the juice box said on it, 100% Vitamin C so I also figured that they added in the Vitamin C.

Nutritional labels with percentages are are usually stated as the percent of the recommended daily allowance (RDA) or recommended daily intake (RDI). Obviously the juice box can't be 100% Vitamin C or it would be a white powder and not a liquid.