Diatom Science Fair Project - i need help! (Oct/26/2005 )
Hello, my name is Corin and I go to North Springs High School in Atlanta, Georgia. I am doing my high school science fair project on diatoms. I will be altering their pH and observing the effects of this under a Scanning Electron Microscope. However, I am not very good at chemistry and need help with the solutions I need to use in order to change the pH. I am planning on using acetic acid and sodium hydroxide. Does anyone that knows anything about chemistry, diatoms, or BOTH have any suggestions? PLEASE HELP ME!
Can you give specifics about what it is you wish to show/prove or disprove with this experiment? By diatoms, I assume you mean the organisms?
Hello, my name is Corin and I go to North Springs High School in Atlanta, Georgia. I am doing my high school science fair project on diatoms. I will be altering their pH and observing the effects of this under a Scanning Electron Microscope. However, I am not very good at chemistry and need help with the solutions I need to use in order to change the pH. I am planning on using acetic acid and sodium hydroxide. Does anyone that knows anything about chemistry, diatoms, or BOTH have any suggestions? PLEASE HELP ME!Hey, Corin! neat project idea!
I have one suggestion for you, that will hopefully help?
pH is very important for living organisms (I'm sure you know this, and that is why you are doing this experiment). whatever else you do, make the changes in small increments. if you simply go up or down by a large amount, you can expect the organisms to croak.
I would take whatever it is the diatoms live in (their 'broth' or 'media' or whatever you are growing them in) and make very small pH changes over a scale that seems appropriate to your goals, and then add some healthy diatoms and see what happens. I would think it would be better to make up the media before adding the organisms to keep from shocking them too much at once? I am assuming you have a pH meter or something similar to measure the changes.
I admit that I know next to nothing about diatoms (just that diatamaceous earth is great in the garden soil), but I think these general guidelines will probably apply?
good luck
I agree with aimikins about doing things in small increments and, like Captain_DNA, would like to hear more about your very interesting project -- maybe we can help you fine-tune it...
I would also point out that diatoms have quite a history with science. They were, after all, the substance (in the form diatomaceous earth, comprised of their skeletons) that Alfred Nobel found would stabilize nitroglycerin, leading to the invention of dynamite (what? you thought that was a random name or something?) and to his fortune, which of course allowed him to establish the Nobel prize.
Diatoms (again, as diatomaceous earth) also played a key role in advancing our ability to purify DNA. DNA binds with great affinity to diatomaceous earth; many of the early miniprep kits were based on this property (largely supplanted by silica membranes now).
Helpful little buggers, aren't they? 
Wow, the Brewman busting with things I didn't even know about them! Way to go! That is interesting info...of course to me anything biology related is interesting, must be why I love my job!
Heehee... I'm just full of useless factoids...!
Here's another one: Later in life, Alfred Nobel suffered from angina pectoris, the remedy for which was then and is still today nitroglycerin. He declined to take it...
Well, I have already cultured some diatoms of the genus Navicula in alga-gro freshwater medium. I know that changing the pH too drastically will kill them and I need to do it in small increments, but the problem I am facing is that I do not know what kind of solutions I need to use in order to adjust the diatoms to my desired pH. I already stated that I am planning on using acetic acid and sodium hydroxide, but I need to know how much to dilute them. I have researched the topic on the internet, but I haven't found anything on what will kill them or what won't. Specifically, I am not trying to find out what will kill them and what won't; I am trying to see if small changes in their pH while they are still living affect the structure of the frustule. So, I need advice on how much I should dilute the chemicals to a point where adding them individually to a neutral solution would change the pH by increments of 0.5.
By the way, thanks for the replies so far!
I would do it empirically because I suspect it would be relatively quick...(do a few diltuions of your acid and base, add tiny bits to a small amount of media, and take a pH...but I dont' know how expensive your media is?)
but, you could do the calculations for the number of moles required to change the pH of your media and then do a dilution of your acid and base that would effect that change. It will likely be a PIA because of the buffering present in your media; another possibility is to call the people that made the media and ask them your ?....if they have good tech support they will make it easy for you.
I agree with Aimikins. The growth media you are using may contain buffers (which resist pH changes). Also you need to know the concentration of the acetic acid and sodium hydroxide you are using. Here is an easy way to alter the pH
-simply to split your media (with the diatoms) in two giant beaker in the chemistry dept (if you have one).
-Stick a pH meter in that sucker and (using a sitrrer) carefully add acid to one until you get the first desired pH.
-Take a sample of that and put in a flask labeled with the pH.
-Continue adding acid to the beaker until you reach your next desired pH.
-Remove a sample into a flask, label, ect...
Continue until you have all your acid pH points. Then take your second half (in the second beaker) and repeat with your base.
You can then let all the flasks grow in identical conditons and them measure their growth.
This is just how I would do it. Other people may have other/better suggestions though. 