What Acids are in fruit juice?

A. Brandon,
Lemon juice is saturated with citric acid . Tomatoes also contain both citric and folic acids. These naturally occurring acids remove tarnish and corrosion from metal surfaces due to the strong positive charge of hydrogen in the acids. The "cationic" hydrogen, along with water moisture, changes (raises) the tarnished coin surface metal to it's ionic (molecular) state; making it dissolve into liquid very easily.

One more thing you might want to tell your son: The term "rust" refers only to the corrosive state of iron. When other metals oxidize, their tarnishing is called corrosion. Pennies are made of copper coated zinc, so they don't "rust".

Any other websites? How dare you? ~8)

A. Lemons contain a lot of citric acid , hence they are known as "citrus fruits" (along with limes and oranges). Tomatoes contain some ascorbic acid (Vitamin C) which is an anti-oxidant and because of this some people believe tomatoes stave off the chance of cancers. Tomatoes also contain malic acid and oxalic acid ( also found in rhubarb); it also contains folic acid, which is useful if you are pregnant! Many fruits contain sugars and when sugars ferment they turn the sugar into alcohol, which in turn can be turned into acetic acid ⇦ this on eBay or Amazon [affil links] - tomatoes are not very rich in sugars, so the acetic acid level will not be very high. Believe it or not, lemons can contain a fair amount of sugar, so potentially a well ripened one could contain acetic acid . All of these acids will clean old pennies given enough time.

A. The orange juice has the most acid over all of lemon juice and whatever the other one was!

A. Do you have a reference you consulted, or an experiment you ran, Dedra -- or was that just a guess? My guess is that you are incorrect and that the right answer is lemon juice. My guess is based on the fact that acids taste sour, and lemon juice tastes more sour to me than orange juice.

The way to actually find out is to test it with pH paper.

Good luck!

A. Hi, Nathan. I feel your pain. Juices are complex mixtures of a hundred or a thousand chemicals, of variable concentration depending on country of origin, ripeness, and other factors -- and it might be wrong for you to try to attribute their cleaning power to acidity alone. Many factors can be involved -- chelation by citric acid s, complexing by tartaric acid ⇦ this on eBay or Amazon [affil links] and the several other acids mentioned by Mr. Crichton, fermentation to alcohol, etc.

Please ask your science teacher for pH paper or a pH meter and try to relate the cleaning ability to the pH of the juice (the acidity of the juice). You will find, though, that you can easily disprove the relationship simply by adding a pinch of salt, which fabulously improves the tarnish removal capability of mild acids like fruit juice.

Best would be to use this project as a chance to practice good lab method. Keep a "lab book" -- this is a notebook where you number the pages in advance of writing anything else so you can't tear pages out and pretend some observation which you made never happened :-)

Then you write down everything you do and everything you see, in ink, with dates and times. The important thing in science is you don't decide in advance what the results of the experiment should be and then mess around until you get them -- that's a poison called "junk science". In real science you immediately write down what you see! This properly done lab book should earn you an "A" whether or not you can fully explain the reason behind the results you got. Good luck, Nathan!

A. I too am doing the same project, look on the US government website under the USDA and they have a breakdown of how much acid is in each different type of orange juice. It sure helped me!

A. Please try the USDA site that Mindy recommended, Darla, and let us know what you find there and what you need that it lacks. We'd appreciate the feedback. Thanks!

I mostly agree with you, Gary. But on those occasions when a student is poorly prepared for what s/he is going to be doing, and we can see that s/he will be reinforcing junk science instead of learning the scientific method, and is on course to learning to despise science instead of embracing it, I think we should try to steer them back on track.

A. Hi Kaleena. I suspect that you don't really have a good understanding of what you mean by "how much acid is in ...?". You might actually be interested in the pH (which is NOT the amount of acid) or the acidity as determined by a neutralization/titration with alkali, or a percentage of citric acid or ascorbic acid, etc., etc.

If you seek an answer to a question without really understanding the question, you're soon stuck in a quagmire. Please try to have a dialog with your teacher until you very clearly understand the question you are trying to find the answer to. Good luck.

Regards,

A. Hi, Ellen. I appreciate your input on this, but personally, I wouldn't do it that way. Rather, I'd pick a practical number of fruit juices of various sorts, and measure the pH before and after the elapse of some time, and THEN try to research a reason for what she finds --

First, your daughter will enjoy it far more because she will be charting new territory with you where mom doesn't already know the answers, rather than trying to keep up with mom's knowledge, which will prove boring for her.

Second, there will be no "junk science" -- trying to talk yourself into seeing things you may not be seeing, and writing off observations as random flaws, as you subconsciously fudge results to try to match notions you think you learned in the research.

Discovering a phenomenon and trying to uncover the reason for what you have discovered is much more fun, far more rewarding, and a lot better science than trying to concoct an experiment to prove somebody else's theory. And it's faster and easier because after you've done the experiment you will know precisely what you are trying to research, rather than just having just some vague notion that there must be something out there that accounts for why different juices may or may not change pH quicker than others.

After you've run the experiment, and then done research on your specific findings to try to account for them, THEN you might run the test again to try to prove that theory, but don't even dream of discarding the results from the first run. Best of luck!

Regards,

A. Hi, Carly. I hate to break it to you, but a pickle is not really a vegetable :-)

It is a cucumber which has been steeped for months in very strong saltwater to replace its natural liquids with this strong salt brine. So its conductivity is owing to the salt brine, not its vegetable nature.

But pick a few fresh vegetables like cucumbers, radishes, potatoes, onions and turnips and see what you get :-)

Regards,

A. Hi, Tashi. Yes, just put the pH paper in the juice, pull it out, and see what color it is, and what pH that indicates.

But please don't "await" a response; this is just a public forum, not a homework hotline :-)

Luck and Regards,

A. Hi, Georgia. I'm not sure what you want help with. You are wanting us to help you by urging you yet again to get pH paper from the teacher? Or are you asking us to take a wild guess at the pH of your particular three pieces of green fruit, and another wild guess of what the pH would be if you picked fruit that was no longer green?

Regards,

A. Hi, Brigid. Sorry, but I really don't understand your quandary at all. You say you are going to do titrations. So, do the titrations with a fresh fruit and do them again when the fruit or the juice is older. What is the complication? You certainly don't want to know the answer to shoot for before you do the titration because that would lead to "junk science" (discounting contrary results, giving too much weight to agreeable results, re-doing the experiment until random factors make it turn out the way you want).

Regards,

A. C'mon students :-)
pH paper is the dead easy way to determine acidity. Until you've mastered pH paper, you're not ready to move on to trickier methods like titration.

Regards,

A. Hi Diana.

You obviously misunderstood your teacher's instructions for the first experiment and already realize that it makes no sense. Don't compound the problem by asking people to guess what your teacher said; ask him/her what was meant.

For the second experiment you need to get ice, salt, and a clock or other timing device. Put measured amounts of ice into two similar containers, and pour a measured amount of salt into one of them, stir it up and carefully record what you see happening. One thing your assignment doesn't mention, but might prove interesting to employ, is a thermometer. You might record the temperature in the two buckets as the ice melts.

There is also one little distortion your experiment introduces. The salt, if room temperature, will warm the ice you put it into. And if the salt is ice cold, then you'll have a larger mass of cold material. It would be ideal to "correct" for this problem by weighing the salt you will add, and then adding an equivalent weight of something else like salt-free sand to the other bucket. Good luck.

Regards,

Hi Sonali. You forgot to attach your photo of the pH paper you dipped into carrot juice so that we could name the color for you ... or maybe I misunderstood the question?

Regards,

A. Litmus paper is a terrible indicator as the range of color change is wide from either red to blue or blue to red.
A short range pH paper would be far better.
The range of carrot juice is any where from 4 to 7, depending on the carrots used, or if it is a commercial juice or the pH of any water that you might use to dilute it. Even how much air that you beat into it will have an effect.
A problem-- Carrot juice is a good stain or dye that will make the pH paper a bit difficult to read and terrible in the yellow/orange range.

A. There is a published color chart of red cabbage juice color vs. pH 1 - 14. You will find it in Rhodiums Drug Chemistry Archive. Besides all the information on how to commit felony crimes (don't get the wrong idea, folks) there's also info on how to purify and dry solvents, properties of common acids/bases, etc.

Thanks for the fascinating post, Dave. I found several archives of Rhodiums Drug Chemistry, and several cabbage juice pH charts, but couldn't tie the two together.

Regards,

A. It is under the "Equipment and Lab Technique" section, with the title "Natural pH indicators" There's also a chart for red beet juice, which is good in the pH 11 - 14 range.

There are also articles on how to build your own magnetic stirrer, your own fume hood, your own glove box, and glass blowing.

How I know about this is I used to sell lab chemicals in Berkeley, CA, and the owner put me in charge of determining whether people were buying chemicals to make dope, explosives, poisons, etc. The lighter side of all this was hearing addled burnouts try to pronounce "phosphorous." Sometimes, they'd put their girlfriends on the phone, 'cause girls can't be criminals. Ha, ha!